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Ergonomics in Sport and Physical Activity
Enhancing Performance and Improving Safety
304 Pages
Ergonomics in Sport and Physical Activity: Enhancing Performance and Improving Safety is the first text to provide an in-depth discussion of how the principles of ergonomics can be applied in the context of sport and other physical activities to reduce injury and improve performance. The textblends concepts from biomechanics, physiology, and psychology as it shows how ergonomics is applied to physical activity.
This comprehensive text outlines methods for assessing risk in and procedures for dealing with stress, eliminating hazards, and evaluating challenges posed in specific work or sport environments. It discusses issues such as the design of effective equipment, clothing, and playing surfaces; methods of assessing risk in situations; and staying within appropriate training levels to reduce fatigue and avoid overtraining. The text not only examines sport ergonomics but also discusses ergonomic considerations for physically active special populations.
Ergonomics in Sport and Physical Activity explains what ergonomics is, how ergonomists solve practical problems in the workplace, and how principles of ergonomics are applied in the context of sport and other physical activities when solving practical problems related to human characteristics and capabilities. The text shows readers how to improve performance, achieve optimal efficiency, enhance comfort, and reduce injuries by exploring topics such as these:
Essential concepts, terms, and principles of ergonomics and how these relate to physical activity Physical properties of the body and the factors limiting performance Interactions between the individual, the task, and the environment Injury risk factors in relation to body mechanics in various physical activities Injury prevention and individual protection in the review of sports equipment and sports environments Comfort, efficiency, safety, and details of systems criteria in equipment design.This research-based text uses numerous practical examples, figures, charts, and graphs to bring the material to life. In addition, descriptions of technological advances show where we have been and how technology has advanced the field. Through the book’s discussion of the various stressors and adaptive mechanisms, readers will learn how to cope with various environmental conditions. They will also learn how various training modes can be used to alter sport-specific capabilities and enhance performance.
Presenting a wide range of approaches, theoretical models, and analytical techniques, Ergonomics in Sport and Physical Activity: Enhancing Performance and Improving Safety illustrates the potential for ergonomics to be extended across recreation, competitive sport, and physically active work environments. Bridging the gap between ergonomics and exercise science, this unique text will assist both health care and exercise professionals in developing an improved awareness of how human capabilities are best matched to physical activities.
Preface
Introduction
Part I. Risk Factors
Chapter 1. Physical Properties of Human Structures
Monitoring Activity Demands
Assessing Individual Characteristics
Assessing Physiological Capabilities
Assessing Mental Load
Overview and Summary
Chapter 2. Health and Safety
Injuries
Predisposition to Injury
Overtraining and Overreaching
Immunosuppression
Risk Assessment
Risk Taking and Fun
Spectator Safety
Human Ethics and Risk
Overview and Summary
Chapter 3. Environmental Stress
Thermoregulation
Altitude
Air Quality
Noise
Overview and Summary
Chapter 4. Circadian Rhythms
Training and Time of Day
Sleep–Wake Cycle
Travel Fatigue and Jet Lag
Sleep Deprivation or Disruption
Nocturnal Shift Work
Overview and Summary
Part II. Sport Ergonomics
Chapter 5. Ergonomics Models and Training Modes in Sport and Leisure
Fitting the Task to the Person
Generic Models
The Training Component
Technological Training Aids
Overview and Summary
Chapter 6. Competitive and Training Stress in Sport
Physiological Loading
Spinal Loading
Physical Loading
Psychological Loading
Overview and Summary
Chapter 7. Sports Equipment and Playing Surfaces
Sports Implements
Sport Surfaces
Sports Clothing
Sport Shoes
Protective Functions of Sports Equipment
Personal Protective Equipment
Overview and Summary
Part III. Ergonomics in Physical Activities
Chapter 8. Fitness for Work
Military Personnel
Prison Officers
Police Officers
Firefighters
Bus Workers and Postal Workers
Drivers
Ambulance Workers
Forestry Workers
Beach Lifeguards
Professional Divers
Workplace Fitness Programs
Overview and Summary
Chapter 9. Special Populations
Young People
Women
Elderly People
Athletes With Disabilities
Match Officials
Overview and Summary
Chapter 10. Clinical Aspects
Predispositions to Injury
Musculoskeletal Loading
Overreaching
Warming Up and Cooling Down
Recovery Process
Prophylactic Measures
Supplements in Clinical Contexts
Artificial Neural Networks
Overview and Summary
Chapter 11. A Holistic and Nutritional Ergonomics Perspective
Participatory Ergonomics
Human Enhancement Technologies
Performance and Cognitive Enhancement
Historical Perspective on Drug Use
From Clinic to Gymnasium
Nutritional Supplements and Over-the-Counter Drugs
Global Ergonomics
Overview and Summary
Afterword
References
Index
About the Author
Thomas Reilly, PhD, DSc, FErgS, FIBiol, was a professor of sport science in the Research Institute for Sport & Exercise Sciences at Liverpool John Moores University in Liverpool, United Kingdom. Reilly’s research focused on the field of sport ergonomics. He conducted research for a wide range of companies and organizations, including GlaxoSmithKline, Mars, the Football Association, the International Olympic Committee, Health and Safety Executive, the European Commission, and various professional soccer clubs and equipment manufacturers. In 2008, Reilly and his research team were awarded the President’s Medal from the Ergonomics Society.
Reilly was a founding member of the European College of Sport Science, established in 1996. He was also a founding member of the Society of Sports Science, which became the British Association of Sport & Exercise Sciences. He was a fellow of the Ergonomics Society, the Institute of Biology, the European College of Sport Science, and the British Association of Sport & Exercise Sciences. Reilly was the founding editor of the Journal of Sports Sciences, holding this position from 1982 to 1997. He served as an editor for special issues in sport ergonomics for the Journal of Applied Ergonomics and Ergonomics.
From 1992 to 2005, he was the chair of the Exercise Physiology Steering Group of the British Olympic Association. Reilly also served as chair of the British Association of Sport & Exercise Sciences from 1994 to 1996 and as chair of the Scientific Committee of the European College of Sport Science from 2003 to 2008.
Tom Reilly passed away on June 11, 2009, as this book was nearing publication.
“The book shines. I have not found any other book that interweaves two concepts [sport science and ergonomics] so successfully.”
—Doody’s Book Review (5-star review)
Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
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Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
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Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
Read more about Ergonomics in Sport and Physical Activity.
Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
Read more about Ergonomics in Sport and Physical Activity.
Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
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Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
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Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
Read more about Ergonomics in Sport and Physical Activity.
Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
Read more about Ergonomics in Sport and Physical Activity.
Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
Read more about Ergonomics in Sport and Physical Activity.
Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
Read more about Ergonomics in Sport and Physical Activity.
Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
Read more about Ergonomics in Sport and Physical Activity.
Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
Read more about Ergonomics in Sport and Physical Activity.
Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
Read more about Ergonomics in Sport and Physical Activity.
Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
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Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
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Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
Read more about Ergonomics in Sport and Physical Activity.
Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
Read more about Ergonomics in Sport and Physical Activity.
Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
Read more about Ergonomics in Sport and Physical Activity.
Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
Read more about Ergonomics in Sport and Physical Activity.
Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
Read more about Ergonomics in Sport and Physical Activity.
Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
Read more about Ergonomics in Sport and Physical Activity.
Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
Read more about Ergonomics in Sport and Physical Activity.
Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
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Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
Read more about Ergonomics in Sport and Physical Activity.
Understand travel fatigue and jet lag
Although international travel is routine nowadays for recreational purposes, it is not without problems for the traveling athlete.
Elite athletes are regularly called upon to travel large distances to participate in international or interclub competitions. Teams may also participate in closed-season tournaments or friendly games overseas as part of preseason training. Such engagements are made possible by the speed of contemporary air flight. Although international travel is routine nowadays for recreational purposes, it is not without attendant problems for the traveling athlete, which should be recognized in advance.
Many athletes have their regular routines disrupted when they travel abroad. They may be particularly excited about the trip or worried about planning for the departure. Depending on the country to be visited, visas and vaccinations may be required. Professional teams usually have arrangements made for them by their administrative and medical staff. These arrangements extend to coping with formal procedures at departure and disembarkation and avoiding any mix-ups in dealing with ground staff and security controls.
Having arrived safely at the destination, the athlete may suffer travel fatigue, loss of sleep (depending on flight times), and symptoms that have come to be known as jet lag. This term refers to the feelings of disorientation, light-headedness, impatience, lack of energy, and general discomfort that follow traveling across time zones (see highlight box). These feelings are not experienced with traveling directly northward or southward within the same time zone when the passenger simply becomes tired from the journey or stiff after a long stay in a cramped posture. Jet lag may persist for several days after arrival and can be accompanied by loss of appetite, difficulty in sleeping, constipation, and grogginess. Although individuals differ in severity of symptoms they experience, many people simply fail to recognize how they are affected, especially in tasks requiring concentration, situation awareness, and complex coordination.
The body's circadian rhythm at first retains the characteristics of the point of departure following a journey across multiple time zones. The new environment soon forces new influences on these cycles, mainly the time of sunrise and onset of darkness. Endogenous circadian rhythms such as core temperature and other measures are relatively slow to adjust to this new context. It takes about one day for each time zone crossed for core temperature to adapt completely. Sleep is likely to be difficult for a few days, but exogenous rhythms such as activity, eating, and social contact during the day help to adjust the sleep-wake rhythm. Arousal state adapts more quickly than does body temperature to the new time zone. Until the whole range of biological rhythms adjust to the new local time and become resynchronized, athletes' performance may be below par.
The severity of jet lag is affected by a number of factors besides individual differences. The greater the number of time zones traveled, the more difficult it is to cope with changes. A 2 hr phase shift may have marginal significance, but a 3 hr shift (e.g., British or Irish teams traveling to play opponents in Russia, or American athletes traveling coast to coast within the United States) will cause desynchronization to a substantial degree. In such cases the flight times-time of departure and time of arrival-may determine the severity of the symptoms of jet lag. Training times might be altered to take the direction of travel into account. Such an approach was shown to be successful in American football teams traveling across time zones within the United States and scheduled to play at different times of day (Jehue et al., 1993).
When journeys entail a 2 to 3 hr time-zone transition and a short stay (2 days), it may be feasible to stay on "home time." Such an approach is useful if the stay in the new time zone is 3 days or less and adjustment of circadian rhythms is not essential. This approach requires that the time of competition coincide with daytime on home time. If this is not the case, then adjustment of the body clock is required. A European team that is to compete in the morning in Japan or in the evening in the United States will require an adjustment of the body clock, because these timings would otherwise be too difficult to cope with.
Symptoms of jet lag recede after the first 2 or 3 days following arrival but may still be acute at particular times of day. There will be a window during the day when time of high arousal associated with the time zone departed from and the new local time overlap. This window may be predicted in advance and should be used for timing of training practices in the first few days at the destination.
The direction of travel influences the severity of jet lag. Flying westward is easier to tolerate than is flying eastward. On flying westward, the first day is lengthened and the body's rhythms can extend in line with their natural free-wheeling period of about 25 hr and thus catch up. Traveling to Japan (9 hr in advance of British Summer Time) and Malaysia (7 hr in advance of British Summer Time) requires more than 9 and 7 days, respectively, for jet lag symptoms to disappear in some individuals. In contrast, readjustment is more rapid on returning to Britain from the east (Reilly, 2003). However, when time zone shifts approach near-maximal values (e.g., a 10-12 hr change) there may be little difference between eastward and westward travel and the body clock is likely to adjust as if the latter had occurred (Reilly et al., 2005).
Sleeping pills have been used by some traveling athletes to induce sleep while on board flight. Drugs such as benzodiazepines are effective in getting people to sleep but they do not guarantee a prolonged period asleep. They were ineffective in accelerating adjustment of the body clock in a group of British Olympic athletes traveling to the United States (Reilly et al., 2001). Besides, these drugs have not all been satisfactorily tested for subsequent residual effects on motor performances such as sport skills. They may in fact be counterproductive if administered at the incorrect time. Nonbenzodiazepine sedatives such as zopiclone and zolpidem have fewer side effects and minimal interference with normal sleep architecture (Lemmer, 2007). Melatonin is one substance that can act directly on the body clock as well as being a hypnotic, but the timing of administration is critical. Travelers between the United Kingdom and Australia, a journey that can elicit the most severe jet lag symptoms, were found to have no benefit from melatonin (Edwards et al., 2000). Melatonin administered in the few hours before the trough of body temperature will have a phase-advance effect whereas if administered in the hours after this trough will delay the circadian rhythm. Ingestion of melatonin at other times will have no chronobiotic effect but will help to induce drowsiness. Drugs do not provide an easy solution to preventing jet lag, and a behavioral approach can be more effective in alleviating symptoms and hastening adjustment (Reilly et al., 2005).
The timing of exposure to bright light is key in implementing a behavioral approach. Light demonstrates a phase-response curve, opposing the effects of melatonin (Waterhouse et al., 1998). Exposure to natural or artificial light before the trough in core temperature promotes a phase delay, whereas a phase advance is encouraged by light administered after this time, meaning "body clock time." Exposure to light at 10 p.m. in Los Angeles following a flight from London would promote a phase advance on the first night rather than the required phase delay, administration occurring after the trough in core temperature (Waterhouse et al., 2007). Where natural daylight cannot be exploited, artificial light from visors or light boxes can be effective for phase-shifting purposes; these commercially available devices have been used in treating seasonal affective disorder found among natives of northern latitudes during the winter seasons when the hours of daylight are limited. The malaise is not a common affliction among athletes.
The athlete should adjust as soon as possible to the local daytime and nighttime in the new environment. Focusing on the local time for disembarkation can help in planning the rest of the daily activity. Natural daylight inhibits melatonin and is the key signal that helps to readjust the body clock to the new environment. There may be other environmental factors to consider such as heat, humidity, or even altitude.
A phase delay of the circadian rhythm is required after traveling westward, and visitors may be allowed to retire to bed early in the evening. Early onset of sleep will be less likely after an eastward flight. In this case, a light training session on that evening will instill local clues into the rhythms. Exercise can hasten the adaptation to a new time zone, and a light training session on the afternoon of arriving in the United Kingdom after a flight has proved beneficial (Reilly, 1993). Training in the morning is not recommended after a long-haul, eastward flight because it exposes the individual to natural daylight and could delay the body clock rather than promote the phase adjustment required in this circumstance. This strategy of avoiding morning sessions until it was deemed appropriate was used by British Olympic athletes arriving in Australia for the Sydney Olympics in 2000.
Exercise should be light or moderate in intensity for the first few days in the new time zone, because training hard while muscle strength and other measures are impaired will not be effective (see figure 4.3). Skills requiring fine coordination are also likely to be impaired during the first few days, and this might lead to accidents or injuries if technical training sessions are conducted too strenuously. When a series of tournament engagements are scheduled, it is useful to have at least one friendly competition before the end of the first week in the overseas country. Naps should be avoided for the first few days because a long nap at the time the individual feels drowsy (presumably at the time he or she would have been asleep in the time zone just departed from) anchors the rhythms at their former phases and so delays the adaptations to the new time zone.
Some precautions are necessary during adjustment to the new time zone. Alcohol taken late in the evening is likely to disrupt sleep and so is not advised. Normal hydration levels may be reduced following the flight because of respiratory water loss in the dry cabin air, and so fluid intake should be increased. A diet recommended for commercial travelers in the United States entailed use of protein early in the day to promote alertness and carbohydrate in the evening to induce drowsiness. This practice is unlikely to gain acceptance among athletes, although they could benefit from avoiding large evening meals. The evening meal might include vegetables with a choice of chipped, roasted, or baked potatoes; pasta dishes; rice; and bread with sufficient fiber to reduce the risk of becoming constipated.
By preparing for time zone transitions and the disturbances they impose on the body's rhythms, the athlete can reduce the severity of jet lag symptoms. There has been little success in attempting to predict good and poor adaptors to long-haul flights. The fact that a person feels relatively unaffected on one occasion is no guarantee that she will do so again on the next visit. Regular travelers benefit from their experiences and develop personal strategies for coping with jet lag (Waterhouse et al., 2002). The disturbances in mental performance and cognitive functions have consequences not only for athletes but also for training and medical staff traveling with them, who are also likely to suffer from jet lag symptoms. The long periods of inactivity during the plane journey may lead to the pooling of blood in the legs and in susceptible people cause a deep-vein thrombosis. Moving around the plane periodically during the journey, say, every 2 hr, and doing light stretching exercises are recommended. Travelers should also drink about 15 to 20 ml extra fluid per hour, preferably fruit juice or water, to compensate for the loss of water from the upper respiratory tract attributable to inhaling dry cabin air (Reilly et al., 2007b). Without this extra fluid intake, the residual dehydration could persist into the early days in the new time zone.
Read more about Ergonomics in Sport and Physical Activity.
Ergonomic considerations for sports clothing
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria.
Clothing ensembles in occupational settings are subject to material standards. The influence of clothing is affected by various factors that include insulation for protection against cold and heat, vapor permeability or capacity for heat loss, air permeability, vapor resistance, and protection from penetration of pollutants. Liquid protection against chemicals and waterproofing for repellence of water and rain are also important properties, as is fire protection for motor racing drivers. The visibility of the garments and their mechanical properties are also relevant. In outdoor conditions the solar absorptivity of clothing is relevant, although this factor is not included in indices such as WBGT (wet bulb and globe temperature) in measuring environmental heat stress.
The appropriateness of the clothing worn for sport participation has been a neglected aspect of its design, because fashion, facilities, and market forces have outweighed ergonomics criteria. The use of size indicators in clothing accommodates inherent differences in participants, but there are often quite radical differences between sports. Loose-fitting clothing is often used in hot climates to keep the microclimate next to the skin cool. The dynamic air exchange, or pumping effect, keeps the area beneath the clothing cool by means of convection and evaporation. Exposure of the skin surface for evaporative cooling may be important for endurance running. Tightly fitting clothing is preferable for enhancing aerodynamic properties of the body in cycling, sprinting, and downhill skiing, for example.
Design of clothing for sprinters has used information from wind-tunnel tests to reduce drag, with the anticipation of improved performance. A whole-body garment was used by Cathy Freeman when winning the Olympic 400 m gold medal at the Sydney Olympics in 2004, although the added value of the latter in terms of energetics is considered marginal. Similar principles have been incorporated into clothing worn by swimmers and ski jumpers. For this latter group, attention has been given to the appropriateness of the traditional ski-jumping boots when extraordinarily high power output must be generated by the jumper at takeoff (Virmavirta and Komi, 2001).
The design of swim clothing has progressed from traditional trunks for male competitors and single (one-piece) suits for females. Mollendorf and colleagues (2004) examined swimsuits varying in body coverage from shoulder to ankle, waist to ankle, and briefs. They measured passive drag at different towing speeds during starts and push-offs in a swimming pool. They concluded that it is possible for body suits that cover the torso and legs to reduce drag and improve performance of swimmers. In a later study, Chatard and colleagues (2008) demonstrated that swim performance over six distances from 25 to 800 m was improved by 3.2% on average when normal swimwear was replaced by a full-body or waist-to-ankle fastskin suit. The gain was greatest with the full-body suit, attributed to a reduction in passive drag, lower energy cost, and a greater distance per stroke. Individuals without access to the new designs of whole-body suits for training might be at a disadvantage in competition. These types of swimsuit formed the majority of those worn at the 2008 Beijing Olympics even though a sizeable proportion of competitors used the more traditional designs. Nevertheless, the advantage of swimsuit technology to reduce hydrodynamic drag has been emphasized by more than a hundred world records achieved by competitors in swimming in the first 12 months of its introduction. Obvious disadvantages are the costs of the suit and the time taken, about 15 minutes, to don it. Six months after the Beijing Olympics, the international governing body FINA clarified the rules about design of swimsuits, specifying that swimsuits must not cover the neck or extend past the shoulders and ankles. The Federation reaffirmed its intention to continue monitoring the evolution of sport equipment with the main objective of keeping the integrity of the sport.
Special clothing may be needed to combat the specific hazards presented in some sports. Motor racing suits may need to offer cooling as well as fireproofing because of the heat stress and risk of fire involved. Many machine sports also require pit staff and drivers to wear ear protectors because of the high noise levels experienced. Wet suits for aquatic sports enable users to tolerate sustained periods of immersion in cold waters. Development of novel fibers has improved protection against wet and cold conditions outdoors while permitting sweat to flow through the garment (Holmer and Elnas, 1981).
Survival time in ocean temperatures not quite ice-cold is increased by wearing dry suits or wet suits. Dry suits are designed to keep the body dry, whereas wet suits allow a minimal amount of water through the material; the water is then heated by the body and, after equalizing with skin temperature and forming part of the boundary layer adjacent to the skin, prevents further loss of heat from the skin surface. Wet suits are usually made of closed-cell neoprene to a thickness of 3 to 6 mm and a close fit is needed for effectiveness. Suits that cover the arms are most effective because more heat is lost from the arms compared to the legs when each limb is exercised at the same oxygen uptake. The time of useful consciousness in water temperatures of 5oC can be extended threefold compared to wearing normal clothing by the use of a neoprene wet suit 5 mm thick but the time is increased by a further 100% if a dry suit is worn with dry underclothing (Reilly and Waterhouse, 2005).
The study of protective garments in a variety of extremes in sports and industrial contexts, such as on the mountains or deserts or in accidental immersion in water, is still a rich vein of ergonomics research. There is a growing demand for merino wool garments, normally used by mountaineering and skiing groups, as a wicking layer. It promotes evaporation of sweat, enhances thermal comfort, and does not smell afterward-a marketing claim for après ski contexts. Comparatively little attention is given to the added value of gloves and headgear in extreme conditions where choice is largely based on subjective evaluation of prevailing environmental conditions.
Sports brassieres have replaced the conventional fashion bra for females competing in track-and-field athletics, road running, and games such as football, squash, and tennis. The original "jog-bra" was designed to reduce movements of the female breast during locomotion and decrease pain and discomfort. Such problems included "jogger's nipple," an irritation also experienced by male runners attributable to chafing from their clothing. A stretchable absorbent fabric such as Lycra is commonly used in sports brassieres. The products are made either with encapsulation molded cups or compression designs that limit motion by flattening the breasts. Their features are incorporated into the running tops worn by some distance runners and triathletes without an accompanying shirt. A concern addressed by Bowles and colleagues (2005) was that sports bras were too tight and restricted breathing. The investigators observed no effect on respiratory function for subjects who wore a sports brassiere, which was superior to a fashion bra and a no-bra condition. The investigators recommended that active females wear a sports brassiere to reduce breast movement and related breast pain. In view of individual differences in size, a proper fit is important. Encapsulated bras are more suitable for large-breasted joggers, whereas compression bras are preferable for the majority of runners. The superiority of the compression bras was demonstrated by White and colleagues (2009) who reported the least discomfort with the compression design. Both sports bras were more comfortable than an everyday bra, while wearing no bra was the most uncomfortable condition. In their kinetic evaluations, White and colleagues demonstrated the importance of curtailing mediolateral, as well as vertical, displacement of the breasts to provide female runners with sufficient support for their performance and comfort during their runs.
Compression garments have been promoted for use in sport as well as other contexts. Compression stockings are commonly used by airline travelers to reduce the risk of incurring deep-vein thrombosis. In sport, compression clothing has been designed to improve recovery following exercise and training. Although this fashion has gained acceptance among professional athletes, the physiological mechanisms for any positive benefit are not clearly established. A similar concept applies to the tight-fitting shirts worn by a number of the teams in the finals of the 2007 World Cup for Rugby Union, with claims of increasing energy levels through transfer of ions to the body. It is unlikely that such interventions determine team success at this level of competition.
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Spinal loading contributes to low back pain
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain.
Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.
Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.
Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.
Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.
Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.
Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.
Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.
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