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Timing Resistance Training
Programming the Muscle Clock for Optimal Performance
by Amy Ashmore
350 Pages
Not just another periodization book, Timing Resistance Training teaches you how to manipulate muscle clocks to train and perform at your best every day—right down to the specific time of day that is best for your body. You will learn to view the muscles as proactive independent physiological systems that can be trained to “think” by delivering timing cues to muscles that tell them when to activate key physiological actions that influence the entire body.
Then you will learn how to cue those internal clocks with purposeful training methods like biomechanical pairing of exercises, complex training, and concurrent training. The book addresses rest as an integral training variable and explores the timing of activity–rest cycles versus recuperation only. The text also discusses the concept of undertraining, an intentional program design adjustment that uses the ability of muscle to anticipate training.
The final chapters offer tools to create your own training programs for strength, power, and flexibility. These chapters include sample single-session workouts, weekly workouts, and long-term programming routines. With Timing Resistance Training, you can become more purposeful in planning and better utilize strategic timing to get the most out of muscles clocks and achieve optimal performance.
Earn continuing education credits/units! A continuing education exam that uses this book is also available. It may be purchased separately or as part of a package that includes both the book and exam.
Chapter 1. What Is a Muscle Clock?
Muscle Clocks: Description and Functions
The Master Clock
Regulation and Communication
Application to Resistance Training
Conclusion
Chapter 2. Overcoming Chaos, Confusion, and Interference
Molecular Competition
Interference Theory
Cardiovascular Endurance Training
Muscular Endurance
Muscle Activation Patterns
Competing Muscle Adaptations
Cardiovascular Training Interferes With Resistance Training
Interference Mechanisms
Avoiding Interference
Resistance-Trained Athletes
High-Intensity Interval Training, Sleep, and Athletes
Evidence From Aerobic Endurance Athletes
Time of Day
Programming Summary
Conclusion
Part II. Learn the Tools for Exercise Programming
Chapter 3. Muscle Clocks’ Need for Cues and Recovery
Environmental Cues
Activity–Rest Patterns
Physiological Cues
Exercise Training and Programming
Conclusion
Chapter 4. Applying Biomechanical Similarity to Resistance and Plyometric Exercises
Biomechanical Similarity
Exercise Categories
Conclusion
Part III. Create Effective Training Programs
Chapter 5. Training Muscles to Think and Anticipate
Motor Learning Influences
Programming
Sample Program
Programming Summary Statements
Age-Related Declines in Anticipation
Conclusion
Chapter 6. Undertraining to Maximize Performance
Training Load
Intentional Undertraining
New Approach to Muscle IQ
Rationales for Undertraining
Benefits of Undertraining
Differentiated Programming
Conclusion
Chapter 7. Using Muscle Clocks to Train for Strength
Paired Exercise Resistance Training Model
Resistance Training Programming
Resistance Exercise Pairing Routines
Sample Workouts
Conclusion
Chapter 8. Using Muscle Clocks to Train for Power
Complex Training
Complex Training Programming
Resistance and Plyometric Exercise Pairing Routines
Sample Workouts
Conclusion
Chapter 9. Using Muscle Clocks for Concurrent Training
Concurrent Training
Competing Mechanisms
Using Muscle Clocks to Avoid Interference in Programming
Cardiovascular Programming to Improve Resistance Training Outcomes
Programming Summary Statements
Conclusion
Chapter 10. Using Muscle Clocks to Improve Flexibility
Flexibility and Muscle Performance
Types of Stretching
Muscle Pliability Is a Timing Cue
Muscle Length
Strength and Power Stimulus
Recovery Aid
Flexibility Programming
Programming Summary Statements
Conclusion
Amy Ashmore holds a PhD in kinesiology from the University of Texas at Austin and an MS in exercise science from Florida State University. She is the author of dozens of articles, blogs, and continuing education programs recognized by National Strength and Conditioning Association (NSCA), Collegiate Strength and Conditioning Coaches Association (CSCCa), American Council on Exercise (ACE), and American College of Sports Medicine (ACSM). Amy was previously on the sports sciences faculty at Florida State University and is the former program director for sports sciences and sports management at American Military University. She is an author and continuing education provider located in Las Vegas, Nevada.
"Amy Ashmore has authored a cutting-edge book that will not only help coaches and trainers set valuable programs in the gym but will also help athletes and fitness enthusiasts achieve pinnacle successes.”
—Kevin McGuire, Managing Editor of American Fitness Magazine
"I have been privileged to have a professional association with Dr. Ashmore for the past 10 years, during which time she has impressed me with her unique ability to effectively bridge the gap between the scientist and the practitioner."
—Cedric X. Bryant, PhD, President and Chief Science Officer of American Council on Exercise
"Amy has been writing and presenting for IDEA since 2002. She can get fitness professionals fully engaged in the complexities of biomechanics and physics. She is an intelligent professional, creative teacher, and superb educator."
—Sandy Todd Webster, Editor in Chief for IDEA Health & Fitness Association
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
Pairing biomechanically similar exercises
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs.
Pairing biomechanically similar exercises is a formula to help exercisers and professionals choose exercises and design workouts and long-term programs. The first step is to focus on a specific muscle group or joint action.
The mode of exercise is a critical programming cue to entrain muscle clocks. Muscle clocks look for biomechanical similarity. The biomechanical similarity is the degree to which two exercises use similar motions and is determined by the primary muscles used and the associated joint actions. Exercise-specific timing cues are based on the primary muscles trained and the primary joints and muscle actions performed. For example, a triceps pushdown is similar to a triceps overhead press, because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action.
Biomechanical similarity is a training method that pairs two exercises that are alike. Pairing exercises that use similar muscles or muscle groups in similar joint patterns provide muscle clocks with invaluable timing cues. The similarity of movements is an entrainment cue that can help muscle clocks establish a schedule and anticipate upcoming training sessions. With biomechanically similar exercises providing consistent clues, muscle clocks learn when to click on the molecular actions associated with resistance training during each 24 h period.
Same or Similar Muscles Used
Biomechanically similar exercises work the same or similar muscles. However, the goal of a paired exercise training model is to activate the same muscles in two different ways. Different movement patterns use different bundles of muscle fibers within the same muscle. For example, both a back squat and leg press train the muscles of the legs and hips. However, each exercise activates slightly different bundles of muscle fibers within the same muscles, differing how they are used. The end programming result is a more comprehensive workout for the entire muscle group. Figures 7.1 and 7.2 illustrate biomechanically paired exercises using the bent-over row and the pullover.
Figure 7.1 Bent-over row: (a) starting position; (b) ending position.
Figure 7.2 Pullover: (a) starting position; (b) ending position.
Understanding timing cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day.
Timing Cues
Muscles learn exercise-specific timing cues from training. Cues are delivered based on the primary muscles trained and the joint actions performed during each exercise when exercises are performed at specific times of the day. For example, a triceps pushdown is similar to a triceps overhead press because both exercises use the triceps muscles as the primary muscle and elbow flexion and extension as the primary joint action. With a regularly scheduled exercise program, the similarity of movement between the two triceps exercises provides muscle clocks with cues about the training mode and type(s) of exercises to anticipate in an upcoming training session and when.
Power exercises are different from strength exercises. Relying on speed, power exercises use plyometric drills that incorporate quicker movements and rely on muscle's ability to generate force after stretching. Because stretch is a primary stimulus for muscle growth, plyometric exercises that deliver timing cues about when stretch will occur and with what exercises provide muscle clocks an unique advantage to prepare for upcoming training sessions to improve muscle performance. Complex training, pairing a strength exercise with an explosive plyometric exercise, adds a new timing cue based on PAP and muscle contractility.
Use of Biomechanically Similar Exercises
Complex training starts with pairing two biomechanically similar exercises, a conditioning exercise plus a plyometric exercise that uses similar muscles and muscle groups and joint actions. For example, the power clean and vertical jump are biomechanically paired exercises that can be used to develop complex paired training sessions. In this case, the conditioning exercise is the power clean (figure 8.5) and the vertical jump (figure 8.6) is the plyometric exercise.
Figure 8.5 Power clean: (a) starting position; (b) transition; (c) catch.
Figure 8.6 Vertical jump: (a) position after countermovement; (b) highest position.
What is a muscle clock?
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity.
Muscle Clocks: Description and Functions
Muscle clocks are transcription factors or genes inside each muscle that regulate physiological cycles according to environmental changes and physical activity. The primary function of muscle clocks is to monitor what happens outside and inside the body during a 24 h period. To help muscles function optimally, muscle clocks pay careful attention to things such as day-night phases, activity-rest cycles, hormone levels, body temperature, and eating and exercise habits.
The discovery of these internal, autonomous regulating clocks in muscle is significant because it shifts how we think about muscles. Muscles are not simply responding to central nervous system commands; instead, the muscles themselves are able to cause action.
Muscle clocks play a role in regulating muscle function. They also communicate with each other, the musculoskeletal system, the brain, and the entire body. Muscle clocks synchronize muscles to the master biological clock in the brain. They also connect muscles to other periphery clocks located in tissues inside and outside the musculoskeletal system.
Muscle clocks are like internal pacemakers. At the cellular level, a molecular clock provides an essential timekeeping method to prepare the muscle for daily changes in the environment. The capacity to synchronize the molecular clock and intracellular activity with outside events, such as day-night cycles, indicates an ability to adapt to environmental conditions. In that way, muscles are smart and show the ability to adapt to their surroundings. An example of another musculoskeletal system clock is a bone clock; an example of a periphery clock is one located in the liver.
Relationship to Muscle Tissue
Muscles make up an estimated 40% to 45% of the body's total mass. Muscle is the single most abundant tissue in the human body. It would make sense, due to its volume alone, that muscle is not simply an effector, a structure under control of the central nervous system that acts only in response to commands. Instead, muscle is an important regulator that causes action in other body systems and has capabilities beyond only responding.
Whatever muscles do affects the entire body. The finding that muscles have clocks that control their functions and communicate with other body systems is revolutionary. It shows that muscles, through a variety of cues, including strategically planned exercise, play a critical role in regulating whole body functioning. For example, with the help of muscle clocks, muscle communicates with the liver and plays an important role in maintaining metabolic homeostasis of the body.
The idea that muscles are more than effectors is not new. Because muscle mass makes up a huge percentage of the human body, it has seemed illogical to many people that muscle's only function would be to act under central nervous system command and execute movements. Although the hypothesis is not new, the evidence to support the idea is new and is explored in detail later in the chapter.
Total Quantity
There are more than 600 skeletal muscles in the human body. Each one has its own muscle clock composed of many different types of genetic material (20, 26). Because humans have more than 600 muscles and each one has its own clock, there are more than 600 individual skeletal muscle clocks working 24 h days to synchronize muscle activity to the master clock in the brain, the other musculoskeletal system clocks, the other body systems, and the environment. Muscle clocks are not one size fits all. Different muscle clocks exist in different muscles made up of different fiber types. The significance of the various types of muscle clocks is discussed later in the chapter.
Composition
Muscle clocks are located inside muscles. They are made up of transcription factors, a sequence-specific binding factor that controls the rate of transcriptionof genetic information (transcription is the process by which genetic information from a thread of DNA is used to produce a thread of complementary RNA) and is involved in the conversion of DNA into RNA (figure 1.1). Once DNA is converted to RNA, the RNA is used to regulate and express genes important to muscle clock function. Transcription factors include essential proteins that initiate and regulate gene activity inside muscle. Each internal clock is made up of numerous transcriptional factors, each with a different role in controlling the clock. Among these transcription factors, some are exclusive to the core molecular clock and some are found across different types of clocks; the muscle clocks also contain genes important for skeletal muscle-specific functions, such as the proteins myosin and troponin, and others important for metabolism and ATP synthesis.
Daily Schedule
All biological clocks are on a 24 h schedule. The 24 h cycle is reflected in daily changes of the whole body, global gene expression pattern, and metabolism. In other words, the transcription factors within the muscle and other clocks behave differently at different times of the day and in response to different stimuli.
The local activity of specific peripheral tissues such as muscles reflect the 24 h cycle of their clocks. Muscle clocks learn a schedule by paying attention to cues outside of the body such as the light-dark cycle, which is associated with the time of day relative to the position of the earth's orbit and is a universal entrainment cue to all biological clocks. (Entrainment refers to the matching of rhythmic biological events, such as the circadian rhythm, to changes in the outside or local tissue environment.) Time-of-day cues set and reset all internal clocks, including muscle clocks. The time of day is the most obvious and well understood clock cue, but as discussed in later chapters, cues are numerous and tissue specific. In the case of muscle, additional cues include hormone levels, activity-rest patterns, and exercise programming (such as the timing of resistance training), all of which are discussed at length in chapter 3.
Figure 1.1 DNA is converted to RNA, which is used to code, decode, regulate, and express genes important to muscle clock function.
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