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Applied Sport Mechanics
264 Pages
This is the loose-leaf version of Applied Sport Mechanics, Fourth Edition, which offers students a printed version of the text at a lower price.
Applied Sport Mechanics, Fourth Edition With Web Study Guide, helps undergraduate students understand how the fundamental laws of human movement affect athletes' performances. Foundational principles of kinetics, kinematics, and sports technique are clearly presented and then explored through a variety of applied scenarios.
What's New
This latest edition builds on the success of the previous editions (formerly titled Sport Mechanics for Coaches), and offers much new material:
• A web study guide with new chapter review questions and practical activities that help students learn and apply complex theories to real-life situations
• An array of updated pedagogical aids, including a glossary and chapter objectives to reinforce learning
• A full-color design for more engaging visual aids
• Reorganized content into two parts and 13 chapters to more readily fit the topics into a typical semester course structure
• Expanded sidebars that apply concepts directly to sport
To make the text applicable for teaching, it also includes a full ancillary package including an instructor guide with a sample syllabus, suggested learning activities, and lecture aids; a test package approximately 20 questions per chapter; and a presentation package plus image bank with ready-made presentations that instructors can use as is or modify to suit their needs.
Content Organization
Part I, which houses the first 10 chapters or 10 weeks, focuses on the fundamentals of sport mechanics. Major topics covered include the anatomy and fundamentals of sport mechanics, linear motion and linear kinetics in sport, angular motion and angular kinetics in sport, stability and instability, sport kinetics, and moving through fluids.
Part II, which contains the final three chapters, helps students apply the information they learned in part I. Chapters 11 and 12 explain how to observe and analyze an athlete's technique and how to correct errors. Students learn how to break a skill into phases and what to look for in each phase. They also learn the mechanical principles that will help them correct the errors. Chapter 13 explores mechanics in a range of sport skills and techniques, including sprinting, jumping, swimming, lifting, throwing, and kicking. Students learn that technique and mechanics are inseparable.
The chapters also contain two helpful types of sidebars: At a Glance sidebars summarize difficult content with bulleted lists, and Application to Sport sidebars bring concepts to life, showing how they work in sport.
Go-To Resource
This fourth edition of Applied Sport Mechanics is a highly practical text, destined to be the go-to biomechanics and sport mechanics resource for instructors and professionals alike in kinesiology and sport related fields.
Part I. Foundations of Movement in Sports
Chapter 1. Introduction to Applied Sport Mechanics
How Applied Sport Mechanics Is Organized
What Is Sport Mechanics?
Understanding and Quantifying Technique
Summary
Key Terms
References
Chapter 2. Sport Mechanics Anatomy
Standard Anatomical Reference Terminology
Connection Between Human Anatomy and Sport Mechanics
Summary
Key Terms
References
Chapter 3. Sport Mechanics Fundamentals
How to Describe Human Motion
Applying Sport Mechanics to Resistance Training
Measurement and Evaluation in Sport Mechanics
Summary
Key Terms
References
Chapter 4. Linear Motion in Sport
Linear Motion Measures (Speed, Velocity, and Acceleration)
Linear Motion for Projectiles
Summary
Key Terms
References
Chapter 5. Linear Kinetics in Sport
Fundamental Principles of Linear Kinetics
Momentum and Impulse in Sport
How to Measure Linear Kinetics: Running Gait
Summary
Key Terms
References
Chapter 6. Angular Motion in Sport
Fundamental Principles of Angular Motion
Applied Angular Motion: How an Athlete Initiates Rotation
Summary
Key Terms
References
Chapter 7. Angular Kinetics in Sport
Gravity: Fundamental Principle of Angular Kinetics
Angular Momentum
Summary
Key Terms
References
Chapter 8. Stability and Instability
Fundamental Principles for Stability
Mechanical Principles for Stability
Factors That Increase Stability
How to Measure Center of Gravity and Line of Gravity for an Athlete
Summary
Key Terms
References
Chapter 9. Sport Kinetics
Work
Power
Energy
Rebound
Friction
Summary
Key Terms
References
Chapter 10. Moving Through Fluids
Fundamental Principles of Moving Through Fluids
Hydrostatic Pressure and Buoyancy
Drag and Lift
Factors That Influence Moving Through Air and Water
Summary
Key Terms
References
Part II. Putting Your Knowledge of Sport Mechanics to Work
Chapter 11. Analyzing Sport Skills
Step 1: Determine the Objectives of the Skill
Step 2: Note Any Special Characteristics of the Skill
Step 3: Study Top-Flight Performances of the Skill
Step 4: Divide the Skill Into Phases
Step 5: Divide Each Phase Into Key Objectives
Step 6: Understand the Mechanical Reasons Each Key Element Is Performed as It Is
Summary
Key Terms
References
Chapter 12. Identifying and Correcting Errors in Sport Skills
Step 1: Observe the Complete Skill
Step 2: Analyze Each Phase and Its Key Elements
Step 3: Use Your Knowledge of Sport Mechanics in Your Analysis
Step 4: Select Errors to Be Corrected
Step 5: Decide on Appropriate Methods for the Correction of Errors
Summary
Key Terms
References
Chapter 13. Selected Sport Skills
Sprinting
Jumping
Wheelchair Sports
Throwing
Striking and Batting
Swinging and Rotating
Weightlifting
Combat Throwing
Tackle in Football
Swimming
Kicking a Ball
Paddling a Watercraft
References
Appendix. Units of Measurement and Conversions
Brendan Burkett, PhD, is a professor at the University of the Sunshine Coast in Queensland, Australia. He received his undergraduate and master’s degrees in engineering and attained his doctorate in biomechanics. Burkett’s teaching specializations are biomechanics, sport coaching, and performance enhancement. His research revolves around technology developments in human health and performance, and he has written more than 150 peer-reviewed articles and 180 conference publications for journals in sport science, biomechanics, and coaching.
As an international elite athlete, Burkett represented Australia for 13 years as a swimmer and was the Paralympic champion, world champion, world-record holder, and multiple medalist in the Commonwealth Games and Australian national championships. He served as the Australian team captain for the 1996 Atlanta Paralympic Games and as the flag bearer for the opening ceremonies of the Sydney 2000 Olympic Games. Following his sporting career Burkett has been the sport scientist for the Australian Paralympic team for the 2002, 2006, 2010, 2010, and 2014 World Championships and the 2004, 2008, 2012, and 2016 Paralympic Games. He has attended the past eight consecutive Paralympic Games, from 1988 to 2016.
Burkett has received several awards, including the Australia Day Sporting Award and the Order of Australia Medal (OAM), as well as induction into the Sunshine Coast Sports Hall of Fame, Swimming Queensland Hall of Fame, and the Queensland Sports Hall of Fame.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
Learn more about Applied Sport Mechanics, Fourth Edition.
Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
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How applied sport mechanics can help you
This benefit is the most important one you’ll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete’s technique.
You will learn to observe, analyze, and correct errors in performance.
This benefit is the most important one you'll get from reading Applied Sport Mechanics. This text will help you develop a basic understanding of mechanics, and by using this knowledge you will be able to distinguish between efficient and inefficient movements in an athlete's technique. The information in this text will help you pick out unproductive movements and follow up with precise instructions that help optimize performance.
- You won't waste time with vague advice like "Throw harder" or "Try to be more dynamic." Obscure tips like these only confuse and frustrate the athletes you're trying to help.
- One of the most effective ways to observe, analyze, and correct errors is through the use of technology, so we've added a section on technology within each chapter to provide you with some additional resources.
On the other hand, if you're the athlete and your coach is not present, a basic knowledge of sport mechanics will help you understand why you should eliminate certain movements in your technique and instead emphasize other actions.
Application to Sport
Advances in Equipment Require Changes in Technique
In the 1998 Nagano Olympics, world records in speed skating were continually broken by athletes using clap skates. The blade on a clap skate is hinged at the front of the shoe but not at the heel. The hinge allows the blade to stay in contact with the ice longer so that the skater is able to thrust at the ice for a longer time. The characteristic clapping noise occurs at the end of each stroke when the blade "claps" back into contact with the heel of the shoe. The clap skate requires a new technique in which the skater must push more directly backward and from the toe rather than out to the side and from the heel. Athletes who were accustomed to the older skates (with the blade permanently joined to the boot at heel and toe) had to adapt to the new equipment and change their technique.
You'll be better able to assess the effectiveness of innovations in sport equipment.
When Greg LeMond of the United States won the Tour de France by a few seconds over Laurent Fignon of France, he certainly illustrated the value of fitness and determination. Equally as important, LeMond and the technicians who assisted him knew the importance of reducing wind resistance to a minimum, particularly during the Tour's final time trial. They realized that if LeMond could maintain a low, dart-like body position that allowed the air to flow smoothly over and past his body, he would spend less energy pushing air aside and could spend more energy propelling himself at high speed.
This knowledge of mechanics paid off! The same principles apply in other sports. You need to know what is gained from design changes in such items as golf clubs, tennis rackets, skis, speed skates, mountain bikes, and swimsuits.
Applied Sport Mechanics cannot teach you all there is to know in the world of sport equipment design, because changes and modifications will continue to occur at an ever-increasing pace. But this text will certainly give you a foundation of knowledge on which you can build.
You'll be better prepared to assess training methods for potential safety problems.
Think of an athlete squatting with a barbell on his shoulders. Where should the athlete position the bar? Should it be placed high on the shoulders or lower down? And what about the angle of the athlete's back during the squatting action? What are the mechanical implications of a full squat compared with half and three-quarter squats? How fast should the athlete lower into the squat position?
- If you know about levers and torque, you'll understand why it's dangerous to bend forward when you squat. Likewise, if you are familiar with the characteristics of momentum and understand how every action has an equal and opposite reaction, you'll know that dropping quickly into a full squat puts tremendous stress on the lower back, knees, and hips. You may have been teaching good technique but don't fully understand why one way of performing the technique is potentially dangerous and another is not. Applied Sport Mechanics will give you the reasons.
- In gymnastics you will frequently see spotting techniques that provide a high level of safety, and you'll also see other techniques that endanger both the gymnast and the spotter.
To explain these concepts further, we've added a new section, "How to Measure," where appropriate within the relevant chapter. This new section describes several ways to measure what is happening in sport that can then be used to assess training methods. By reading Applied Sport Mechanics you'll discover, for example, why efficient spotting requires an understanding of balance, levers, torque, and the momentum generated by the gymnast performing the skill.
This information will help you teach safe spotting techniques in gymnastics and good technique in weight training. Of course, Applied Sport Mechanics is not limited to these two sports. You can apply the mechanical principles that you read about to every sport.
You'll be better able to assess the value of innovations in the ways sport skills are performed.
In sport, our capacity for reasoning and creativity has been responsible for the advances in talent selection, technique, training, and equipment design. We all possess a tremendous capacity for creativity. Coaches must use this creativity to search for better ways to improve their athletes' performance. All athletes differ in physique, temperament, and physical ability; what works for one athlete will not necessarily work for another. Similarly, a young athlete will differ dramatically from a mature athlete.
- To help athletes achieve top-flight performances, coaches should learn why sport techniques are performed as they are and be prepared to modify certain aspects of these techniques to fit the athletes' age, maturity, and experience. There are many examples of the willingness of coaches and athletes to try out new ideas.
- In team games, coaches modify attack and defense formations relative to the team they will face in an upcoming contest.
Among athletes, think of how the creativity and experimentation of Dick Fosbury revolutionized the high jump. Similarly, the glide and rotary techniques have increased the distances thrown in the shot put. In gymnastics, consider the number of skills named after their creative inventors (such as the "Thomas Flair," named after former U.S. gymnast Kurt Thomas).
So be curious and learn the how and why of technique. At the same time, be creative and willing to experiment. Coaches should to encourage their athletes to use their own creative capacities as well. They should always look for ways to improve their understanding of the sport they are coaching. They can be a coach, an analyst, and an innovator all at the same time!
You will know what to expect from different body types and different levels of maturity.
If you understand the mechanical principles governing the techniques of your sport, you'll understand why young athletes (who are growing quickly) have a tougher time maneuvering, changing direction, and coordinating their movements than more mature athletes do.
- You'll realize that young athletes cannot follow the same training regimens used by more mature athletes.
- You'll also understand why tall athletes with long arms and legs have an edge in some sports but are at a disadvantage in others.
Similarly, you will realize why smaller athletes tend to have a good strength-to-weight ratio and can cut, turn, and shift more quickly than athletes who are taller and heavier.
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Understand the mechanical reasons for each key element
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics.
Understanding the mechanical basis behind each key element is an important step in your sequence. The first 10 chapters laid the foundations of principles of sport mechanics. By analyzing technique we are putting this knowledge into practice - in essence, practicing applied sport mechanics.
All fundamental actions that an athlete takes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws. So after you've picked out the key elements in the skill you are analyzing, you have to understand the mechanical purposes behind each element. You must be able to answer questions such as the following with responses like the ones listed here.
Why cock and uncock the wrists during a golf drive?
Cocking and uncocking the wrists during a golf drive causes the golfer's arms and club to simulate the whiplash, or flail-like, action of the high-speed tip segments of a whip (see figure 11.4c-11.4e). When the wrists are cocked and uncocked, they act as an additional axis around which the club can rotate. The velocity developed from the swing (and length) of the golfer's arms is multiplied along the length of the club shaft (Fedorcik et al. 2012). Without the cocking and uncocking action, the arms and club would move as a fixed unit. This action would not allow the head of the club to reach optimal velocity.
Why should a sprinter's legs and arms thrust and swing parallel to the direction of sprint during a 100 m sprint?
If a sprinter's arm swing and leg thrust (see figure 13.1) in any direction other than parallel to the direction of sprint, the forces that the sprinter applies to the earth in the direction of sprint are reduced. In reaction, the force that the earth applies against the sprinter is lessened as well. The result is that the sprinter doesn't run as fast as possible.
Why should a freestyle swimmer pull with the hands and forearms along a line parallel to the long axis of the body rather than emphasize an S-shaped out - in - up - down pattern of pull?
Emphasizing an S-shaped out - in - up - down motion with the hands during the freestyle stroke, as shown in figure 13.10, is now thought to generate less propulsive force than pulling straight back against the water. A modified S-shaped motion still occurs during entry and exit of the swimmer's hand, but these actions occur more from body roll and the anatomy of the swimmer's body than from efforts to generate more propulsion. Pulling back against the water as far as possible parallel to the long axis of the body is now considered the correct technique. Under water, the arms flex at the elbows so that the swimmer's hands and forearms provide the major propulsive surfaces.
Why must athletes have their center of gravity positioned behind the jumping foot as they enter a high-jump takeoff or behind both feet as they prepare to jump to block or spike in volleyball?
Positioning the takeoff foot ahead of the center of gravity gives the athlete more time to apply force with the jumping leg at takeoff (see figure 13.2). The athlete rocks forward, up, and then over the jumping foot. This large arc of movement gives the athlete time to drive down at the earth. The earth in reaction drives the athlete upward. The same principle applies to a volleyball spike, a volleyball block, a basketball layup, and a basketball block.
Why is it important for athletes to rotate the hips and thrust them ahead of the upper body during a golf drive, shot put, and discus or javelin throw?
Rotating the hips ahead of the upper body and toward the direction of throw serves three purposes. First, it shifts the athlete's body mass in the proper direction (i.e., toward the direction in which the golf club, discus, shot, javelin, or baseball bat will be accelerated). This action extends the distance and time over which the athlete applies force. Second, the rotation of the hips acts as an important link in the sequential acceleration of the athlete's body segments. The movement of the athlete's legs and hips toward the direction of throw (or impact with the ball in golf or baseball) simulates swinging a whip handle ahead of the rest of the whip so that the tip of the whip cracks. Third, the rotation of the hips stretches the muscles of the abdomen and chest so that they pull the shoulders and throwing arm in slingshot fashion toward the direction of throw. (Notice the weight shift and hip action in the javelin throw in figure 13.4 and in the golf drive in figure 11.4.)
Why should athletes extend the kicking leg when contacting the ball in a football punt?
By extending the kicking leg, the athlete puts the part of the foot that contacts the ball farther from the axis of rotation (i.e., the hip joint). Because of this increase in radius, the kicking foot is moving faster than any other part of the leg when it contacts the ball. The flexion of the kicking leg before contact with the ball, together with its extension at impact, simulates a whiplash action (see figure 13.11).
At a Glance
Analyzing Sport Skills
- One of the greatest challenges you'll face working in sport is watching the athlete perform and deciding which aspect of the skill needs correction (if any).
- All fundamental actions that an athlete makes within technique are founded on mechanical principles. In other words, technique is based on mechanical laws.
- After you have analyzed the performance, you need to communicate this information to the athlete. Technology can be an effective mechanism for providing feedback.
Why must athletes extend their bodies fully at takeoff in gymnastics and diving skills?
Athletes who need to rotate quickly must apply an eccentric thrust, or an off-center force, at takeoff to initiate rotation. They must then pull the body inward from a fully extended position. The large reduction in rotary inertia caused by compacting the body mass around the axis of rotation is rewarded by a huge increase in the rate of spin (i.e., angular velocity).
All phases and all key elements in a skill are performed for specific mechanical purposes. If you know the mechanical reasons that they're performed as they are, you can confidently say to yourself, "OK, I understand what should occur in the technique of this skill, and I understand the mechanical principles behind the movements that the athlete must perform. I'm ready to watch my athlete and correct any errors that I find."
We have asked you to use elite performances as a model or reference point when working in a sport. But don't make the mistake of trying to mold a young athlete in the exact image of a high-performance athlete. When you watch a series of top performances, be sure to study the basic technique that these top athletes use - nothing more. With your knowledge of mechanics, you'll see the purpose behind these actions. As your knowledge of sport mechanics improves, you'll learn to disregard some actions that a top-class athlete uses because they are personal idiosyncrasies of no mechanical value. Accept them as something that makes an individual athlete comfortable but disregard them as a necessity for good performance.
Remember that the actions that an elite athlete performs at high velocity over a great range of movement need to be modified to be appropriate for the maturity, strength, flexibility, and endurance of a young athlete. You cannot and must not expect a young, immature athlete or a novice of any age to assume the body positions or match the explosive actions of an experienced athlete. This development comes with regular training and good coaching.
Application to Sport
Rowers Use Hatchet Blades to Apply More Force
High-performance rowers use oars with huge blades that look like giant meat cleavers. Called hatchet blades, these oars are shorter from the oarlock to the blade than standard oars are. The mechanical principle behind this design is that for the same effort from the rower, the hatchet blade travels more slowly through the water but applies more force. Moving slower, the blade slips less in the water but propels the shell faster. Do these blades present any problems? According to many coaches, hatchet blades, although allowable within the rules of rowing at many levels, can cause stress injuries in the lower and upper limbs because the rowers have to pull against a stiffer and less mobile resistance.
Learn more about Applied Sport Mechanics, Fourth Edition.
Making use of angular momentum
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies.
When tower or springboard divers are in flight, they no longer have a large mass to push against. Any muscular action they perform while in the air causes an equal and opposite reaction to occur elsewhere in their bodies. All divers, gymnasts, and other high-flying athletes experience this phenomenon.
For example, imagine a diver stepping off the tower and dropping toward the water in an upright position. In this position, he is not rotating. As the diver drops, imagine the coach shouting for him to raise his extended legs 90° from perpendicular (i.e., pointing directly downward) to horizontal. The muscles that rotate his legs forward and upward around the hip joint pull equally at both origin and insertion (i.e., at either end of the muscle) and therefore simultaneously pull down on his trunk. As a result, during the period that the diver's legs rotate upward, his trunk must rotate downward. Do his legs and trunk rotate in equal-size arcs?
No, because they do not have the same rotary inertia. The rotary inertia of the diver's trunk and upper body is approximately three times that of his legs. Therefore, his trunk and upper body resist rotation three times more than his legs do. When the diver's legs move upward 90° to a horizontal position, the trunk and upper body, which have three times more rotary resistance, move downward in an arc a third of the size, or approximately 30° (see figure 7.8).
Figure 7.8 When the diver's extended legs are raised 90° in a counterclockwise direction, the upper body reacts by moving 30° in a clockwise direction.
The movement of the diver's legs and that of his trunk and upper body may not seem like equal and opposite reactions, yet they are. In our example, the action is the 90° arc moved in a counterclockwise direction by the diver's legs. The reaction is the 30° arc moved in a clockwise direction by their trunk and upper body. This reaction is equal to the action because the diver's trunk and upper body have three times the rotary inertia of the legs. The reaction is opposite because the movement of the trunk and upper body is in the opposing direction to that of the legs.
We've seen that rotary inertia depends not only on how much mass is involved but also on how it is distributed relative to its axis. In the previous example, the diver keeps his legs extended throughout their 90° movement. If the diver flexes at the knees and lifts at the thighs, then the rotary inertia of the legs is reduced. The reaction of the trunk and upper body is also reduced. The upper body and trunk flex approximately 20° (see figure 7.9).
Figure 7.9 When the diver's flexed legs are raised, they have less rotary inertia than when they are raised in an extended position. The upper-body response is less.
Figure 7.10 shows that another reaction will occur in the diver's movements. Notice that as the diver's extended legs rotate counterclockwise, the trunk and upper body rotate clockwise. In the illustration, these body parts move toward the right as you look at them. In the air, body mass moving to the right is counterbalanced by body mass moving to the left. In our example the diver's buttocks and hips react (equal and opposite) by moving toward the left.
Figure 7.10 In the air, when the lower and upper body flex forward, the hips react by shifting backward
This phenomenon of equal and opposite reactions occurring in the air is visible in many sports. A flop-style high jumper always arches to clear the bar. Figure 7.11 shows a high jumper arching the upper body down toward the pit in a counterclockwise direction. The legs respond (equal and opposite) by moving in a clockwise direction. Although upper body and legs are moving in opposing directions, both are moving down toward the pit. So the hips react by moving upward. By correctly timing this action, the high jumper can pass over the bar. The hips and buttocks move upward to help the athlete clear the bar.
Learn more about Applied Sport Mechanics, Fourth Edition.
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