INTRODUCTION
THE WHO, WHAT, WHY, AND HOW OF PERSONAL
TRAINING
TOPICS COVERED IN THIS UNIT
Personal Training
Who Wants Personal Training?
What is a Personal Trainer?
Why is Personal Training Necessary?
What Should a Personal Trainer Know?
ISSA Code of Ethics and Standards
Principles and Purpose
Academic Standards
Professional Standards
U.S. President Theodore Roosevelt
PERSONAL TRAINING
Today’s fitness industry is a multibillion-dollar business. Personal training is its evergrowing offspring. The roots of personal training are difficult to pinpoint. Some credit its
origin to be in the 1950s (when personal trainers were first actively certified), although one
could contend that personal training dates back to the beginning of recorded history.
While the profession and terminology associated with personal training were not yet in
existence, the concept of optimal health (which is the motivation behind the profession)
was already being touted by ancient philosophers. Around 400 BC, Hippocrates wrote
this:
“Eating alone will not keep a man well; he must also take exercise. For food and exercise,
while possessing opposite qualities, yet work together to produce health … and it is
necessary, as it appears, to discern the power of various exercises, both natural exercises
and artificial, to know which of them tends to increase flesh and which to lessen it; and
not only this, but also to proportion exercise to bulk of food, to the constitution of the
patient, to the age of the individual.”
Of all of the leaders of the United States, Theodore Roosevelt was one of the strongest
presidents, both physically and mentally. However, he did not start that way. As a child,
Roosevelt was small for his age and quite sickly. He had debilitating asthma, had poor
eyesight, and was extremely thin. When he was 12 years old, his father told him,
“You have the mind, but you have not the body, and without the help of the body, the
mind cannot go as far as it should. You must make the body.”(Morris, 1979).
Roosevelt began spending every day building his body as well as his mind. He worked out
with weights, hiked, hunted, rowed, and boxed. History can attest: Theodore Roosevelt’s
strength in mind and body contributed to his strength as the leader of his nation.
Another great leader was U.S. President John Kennedy. Like Roosevelt, Kennedy
acknowledged the benefits of physical activity for optimal health. He once said,
“Physical fitness is not only one of the most important keys to a healthy body, it is the
basis of dynamic and creative intellectual activity.”
WHO WANTS PERSONAL TRAINING?
According to the International Health, Racquet & Sports Club Association and American
Sports Data (IHRSA/ ASD) Health Club Trend Report, since 1998, the number of
Americans belonging to health clubs has grown 45 percent (about 14 million members).
Health club memberships among children under 18 years of age have jumped by 187
percent since 1987. The number of clients considering personal training services continues
to grow. According to IHRSA’s Annual Health Club Consumer Study (2014), 52.9 million
Americans aged 6 years and older are members of health clubs. Over 12 percent of these
members pay for the services of a personal trainer and over 6 million health club members
alone paid for a personal trainer this past year. In-home sessions, park boot camp
sessions, and other non traditional training sessions were not included in gym data.
Here are some statistics from the report:
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Three out of five clients are women.
Clients report an average of 18 sessions with a trainer.
Trainers charge between $15 and $100 per hour—an average of $50 per hour.
Average sessions used in 12 months are as follows:
Sessions
Percentage
1–6
47%
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7–11
12%
12–24
11%
25–49
8%
50 +
11%
Not Reported
11%
Number of sessions clients used by age are as follows:
Age Range
Sessions
6–11
22
12–17
26
18–34
15
35–54
14
55 +
24
These statistics support the growing trend and need for personal training services. While
those 4 million people who purchased personal training services are sold on the need for
personal training, let’s explore what exactly is a personal trainer?
WHAT IS A PERSONAL TRAINER?
The profession of personal training is a relatively new field that continues to expand its
boundaries and redefine itself. Prior to the early 1980s, no minimal requirements existed
to qualify or identify a person as a personal trainer. Those engaged in training were still an
esoteric group. Many learned about training solely through personal experiences in the
gym. Recognizing the need for standardization and credibility, Dr. Sal Arria and Dr. Fred
Hatfield pioneered a program of personal fitness training that merged gym experience
with practical and applied sciences.
Today, a personal fitness trainer can be defined as a person who educates and trains
clients in the performance of safe and appropriate exercises in order to effectively lead
them to optimal health. Personal trainers can be self-employed or work in health clubs,
physicians’ offices, physical therapy clinics, wellness centers, hospitals, rehabilitation
facilities, and private studios.
WHY IS PERSONAL TRAINING NECESSARY?
The U.S. Surgeon General’s Report on Physical Activity and Health supports the role of
physical activity for good health and disease prevention. The National Institutes of Health
released a consensus statement on the importance of physical activity for cardiovascular
health (US Department of Health and Human Services,). In addition, the Centers for
Disease Control and Prevention (CDC) launched the Healthy People Initiative, which lists
physical activity, fitness, and nutrition at the top of twenty-two priority areas. Finally, the
American Heart Association included physical inactivity and low fitness levels as primary
risk factors, along with smoking, hypertension, and high cholesterol.
Unfortunately, although the resounding benefits of physical activity and fitness are touted
and reported, the United States is currently undergoing an obesity epidemic. In the United
States, 25 to 35 percent of people remain sedentary. To make matters worse, federal
resources and funds for physical activity have lagged far behind other aspects of health.
Health and physical education in schools are low priorities, and when districts are looking
to trim their budgets, health and physical education programs are often the first to be cut.
Consider the following: Each year in the United States, people spend $2.5 trillion on
health care. This meteoric figure translates into an expenditure of almost $7,000 for each
member of the U.S. population. Regrettably, this financial commitment has neither shown
signs of abating nor has it produced satisfactory results with regard to treating a wide
variety of chronic health problems.
Attempts to identify the factors that have been major contributions to this virtual epidemic
of medical problems have produced a litany of probable reasons why such a large number
of individuals are so apparently unhealthy, including poor eating habits, sedentary
lifestyle, stress, and poor health habits (e.g., smoking). At the same time, a number of
studies have been undertaken to identify what, if anything, can be done to diminish either
the number or the severity of medical problems affecting the public. These studies have
provided considerable evidence that exercise has substantial medicinal benefits for people
of all ages.
Two of the most widely publicized efforts to investigate the possible relationship between
exercise and disease were longitudinal studies, each of which involved more than 10,000
subjects. In a renowned study of 17,000 Harvard graduates, Ralph Paffenbarger, MD,
found that men who expended approximately 300 calories a day (the equivalent of walking
briskly for 45 minutes) reduced their death rates from all causes by an extraordinary 28
percent and lived an average of more than 2 years longer than their sedentary classmates.
Another study conducted by Steven Blair, PED, of the Institute of Aerobics Research in
Dallas documented the fact that a relatively modest amount of exercise has a significant
effect on the mortality rate of both men and women. The higher the fitness level, the lower
the death rate (after the data were adjusted for age differences between subjects in this 8year investigation of 13,344 individuals). An analysis of the extensive data yielded by both
studies suggests one inescapable conclusion: Exercise is medicine!
Accepting the premise that regular exercise can play a key role in reducing your risk of
medical problems and in decreasing your ultimate costs for health care is critical. Despite
the vast number of individuals who lead a sedentary lifestyle, the need for and the value of
exercising on a regular basis is an irrefutable fact of life (and death). For example, after a
detailed review of the results of his long-term investigation, Dr. Paffenbarger concluded
that not exercising had the equivalent impact on a person’s health as smoking one and a
half packs of cigarettes a day. Fortunately, with few exceptions, most people are too
sensible to ever consider ravaging their health by smoking excessively. Unfortunately,
many of these same people fail to recognize the extraordinary benefits of exercise in the
prevention of medical problems.
Any listing of the medical problems and health-related conditions that can be at least
partially treated and controlled by exercise would be extensive. Among the most
significant of these health concerns and the manner in which exercise is thought to help
alleviate each condition are the following:
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Allergies. Exercise is one of the body’s most efficient ways to control nasal congestion
(and the accompanying discomfort of restricted nasal blood flow).
Angina. Regular aerobic exercise dilates vessels, increasing blood flow — thereby
improving the body’s ability to extract oxygen from the bloodstream.
Anxiety. Exercise triggers the release of mood-altering chemicals in the brain.
Arthritis. By forcing a skeletal joint to move, exercise induces the manufacture of
synovial fluid, helps to distribute it over the cartilage, and forces it to circulate throughout
the joint space.
Back pain. Exercise helps to strengthen the abdominal muscles,the lower back extensor
muscles, and the hamstring muscles.
Bursitis and tendinitis. Exercise can strengthen the tendons — enabling them to
handle greater loads without being injured.
Cancer. Exercise helps maintain ideal bodyweight and helps keep body fat to a minimum.
Carpal tunnel syndrome. Exercise helps build up the muscles in the wrists and
forearms, thereby reducing the stress on arms, elbows, and hands.
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Cholesterol. Exercise helps to raise HDL (high-density lipoprotein—the “good”
cholesterol) levels in the blood and lower LDL (low-density lipoprotein—the undesirable
cholesterol) levels.
Constipation. Exercise helps strengthen the abdominal muscles, thereby making it
easier to pass a stool.
Depression. Exercise helps speed metabolism and deliver more oxygen to the brain; the
improved level of circulation in the brain tends to enhance mood.
Diabetes. Exercise helps lower blood sugar levels, strengthen the skeletal muscles and
heart, improve circulation, and reduce stress.
Fatigue. Exercise can help alleviate the fatigue-causing effects of stress, poor circulation
and blood oxygenation, bad posture, and poor breathing habits.
Glaucoma. Exercise helps relieve intraocular hypertension (the pressure buildup on the
eyeball that heralds the onset of glaucoma).
Headaches. Exercise helps force the brain to secrete more of the body’s opiate-like, paindampening chemicals (e.g., endorphins and enkephalins).
Heart disease. Exercise helps promote many changes that collectively lower the risk of
heart disease—a decrease in body fat, a decrease in LDL cholesterol, an increase in the
efficiency of the heart and lungs, a decrease in blood pressure, and a lowered heart rate.
High blood pressure. Exercise reduces the level of stress-related chemicals in the
bloodstream that constrict arteries and veins, increases the release of endorphins, raises
the level of HDL in the bloodstream, lowers resting heart rate (over time), improves the
responsiveness of blood vessels (over time), and helps reduce blood pressure through
maintenance of body weight.
Insomnia. Exercise helps reduce muscular tension and stress.
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Intermittent claudication. Claudication is pain caused by too little blood flow to the
extremities. Exercise helps improve peripheral circulation and increases pain tolerance.
Knee problems. Exercise helps strengthen the structures attendant to the knee
(muscles, tendons, and ligaments) thereby facilitating the ability of the knee to withstand
stress.
Lung disease. Exercise helps strengthen the muscles associated with breathing and
helps boost the oxygen level in the blood.
Memory problems. Exercise helps to improve cognitive ability by increasing the blood
and oxygen flow to the brain.
Menstrual problems and PMS. Exercise helps to control the hormonal imbalances
often associated with PMS by increasing the release of beta-endorphins.
Osteoporosis. Exercise promotes bone density, thereby lowering an individual’s risk of
experiencing a bone fracture.
Overweight problems. Exercise is an appetite suppressant. It also increases metabolic
rate, burns fat, increases lean muscle mass, and improves self-esteem—all factors that
contribute to healthy weight.
Varicose veins. Exercise can help control the level of discomfort caused by existing
varicose veins and help prevent additional varicose veins.
Are the positive effects that result from exercising regularly worth the required effort?
Absolutely. Should you make exercise an integral part of your daily regimen? Of course,
you should. In countless ways, your life may depend on it. The meteoric rise of health care
and health problems makes your success as a personal trainer predictable.
Implications for Certified Fitness Trainer
Professionals
The need for personal training services continues to grow. As future ISSA fitness
professionals, it is imperative that we keep up with the evolving recommendations for
health and physical fitness that have a direct application for fitness programs and exercise
recommendations. With the emergence of the latest technologies, information regarding
health and fitness is easily accessible. However, because of the nature of the media’s use of
vague and brief headlines in conjunction with radio and television sound bites that provide
only limited, confusing, and often conflicting recommendations, it is important that we
can help our clients, friends, and family members put each new study or report in proper
perspective. Personal trainers today are committed to a long-term career in health and
fitness and are increasing their knowledge through additional courses in postrehabilitation, corporate wellness, youth fitness, senior fitness, and pre- and postnatal
specializations to better serve their clients in achieving and living the fitness lifestyle. As
you can see, we as personal trainers have an inherent responsibility to positively influence
the health and fitness attitudes of those around us. Individually and collectively, we can
bring health and fitness to the masses and make the dream of optimal health a reality for
all.
WHAT SHOULD A PERSONAL TRAINER KNOW?
As the industry continues to expand its boundaries and the realm of scientific knowledge
concerning the human response and adaptation to exercise continues to grow, it is
essential that personal fitness trainers be competent in the following:
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Exercise programming
Exercise physiology
Functional anatomy and biomechanics
Assessments and fitness testing
Nutrition and weight management
Basic emergency procedures and safety
Program administration
Human behavior and motivation
Our ability as fitness professionals to educate and effectively draw our clients into the
fitness lifestyle and optimal health comes from a plan that is based in the aforementioned
areas as well as the knowledge of
muscular, cardiopulmonary, and metabolic adaptations. These adaptations are known as
the training effect. The training effect is the body’s adaptation to the learned and expected
stress imposed by physical activity. When the body experiences the training effect, it
begins to change at the cellular level, allowing more energy to be released with less oxygen.
The heart and capillaries become stronger and more dispersed in order to allow a more
efficient flow of oxygen and nutrients. The muscles, tendons, and bones involved with this
activity also strengthen to become more proficient. In time, the body releases unnecessary
fat from its frame, and stride and gait become more efficient. Additionally, resting heat
rate and blood pressure drop. These adaptations can be achieved through an educated
trainer who can develop an appropriate fitness and health plan.
The fitness and health plan must account for the basic principles of fitness training:
overload, specificity, individual differences, reversibility, periodization, rest, overtraining,
and stimulus variability. The plan requires a thorough understanding of the major muscles
of the body and how they work, as well as an understanding of metabolism—how the body
converts food energy into other forms of energy it can use at rest and during exercise. In
addition, trainers must learn about the function and regulation of the lungs, heart, blood
vessels, hormones, brain, and nerves, as well as the weight control and temperature
regulation systems at rest and during exercise. Once you have the knowledge and support
to develop comprehensive, individualized, and periodized plans that effectively produce
the training effect, then you will be able to effectively draw your friends, family members,
and future clients into the fitness lifestyle and optimal health.
Over a quarter century ago, Dr. Sal Arria and Dr. Fred Hatfield had a vision to
pioneer a personal fitness trainer program that would merge in-gym
experience with practical and applied sciences in order to share the benefits
of the fitness lifestyle with the masses. As the profession continues to grow
and expand its boundaries, for the ISSA trainer of today and the ISSA trainer
of tomorrow, education and support are vital. It is the hope and vision of the
ISSA that through this course text and the support provided by the entire
ISSA staff, ISSA-certified trainers will continue to be more educated than in
the past; they will be well-rounded and knowledgeable about exercise and
how it relates to optimal health and fitness.
ISSA CODE OF ETHICS AND STANDARDS
Principles and Purposes
Upon receipt of the ISSA Certificate, members become, in effect, de facto representatives
of the leader in the fitness certification industry, and as such are expected to conduct
themselves according to the highest standards of honor, ethics, and professional behavior
at all times. These principles are intended to aid ISSA members in their goal to provide the
highest quality of service possible to their clients and the community.
Academic Standards
Requirements for Graduation
1. Certification will not be issued to any student/ member who does not successfully
complete or meet all pertinent qualifications or has not achieved passing scores on the
relevant ISSA examinations.
2. Certification will not be issued to any student/ member unless they have successfully
completed CPR/AED training as evidenced by a current and valid CPR/AED card.
3. Certification will not be issued until all fees are paid in full.
Professional Standards
ISSA members will do the following:
1. Serve clients with integrity, competence, objectivity, and impartiality, always putting the
clients’ needs, interests, and requests ahead of his or her own. Members must always
strive for client satisfaction.
2. Recognize the value of continuing education by upgrading and improving their knowledge
and skills on an annual or semi-annual basis. Members must keep abreast of relevant
changes in all aspects of exercise programming theory and techniques.
3. Not knowingly endanger his or her clients or put his or her clients at risk. Unless they have
allied health care licenses, members must stay within the realm of exercise training and
lifestyle counseling with clients. Clients with special medical conditions must be referred
to proper medical professionals.
4. Never attempt to diagnose an injury or any other medical or health-related condition.
5. Never prescribe or dispense any kind of medication whatsoever (including over-thecounter medications) to anyone.
6. Never attempt to treat any health condition or injury under any circumstance whatsoever
(except as standard first aid or CPR procedure may require).
7. Never recommend exercise for anyone with a known medical problem without first
obtaining clearance to do so and/or instructions from the attending qualified medical
professional.
8. Ensure that CPR certification and knowledge of first aid procedures is current.
9. Work toward the ultimate goal of helping clients become more self-sufficient over time,
reducing the number of supervised training sessions.
10.Respect client confidentiality. All client information and records of client cases may not be
released without written release from the client.
11. Charge fees that are reasonable, legitimate, and commensurate with services delivered and
the responsibility accepted. All additional fees and services must be disclosed to clients in
advance.
12. Adhere to the highest standards of accuracy and truth in all dealings with clients, and will
not advertise their services in a deceptive manner.
13. Not get intimately involved with their clients. Minimize problems by always maintaining a
professional demeanor, not becoming overly friendly with clients, and documenting
training sessions, evaluations, and training programs. We cannot overemphasize this
point: Be a professional; do not get personally involved with clients!
14. Price cutting (also called low balling) is a sales technique that reduces the retail prices of a
service so as to attempt to eliminate competition. It can also potentially eliminate your
ability to make a living. Corporate gyms hire trainers with little to no experience and
charge members minimally $50 per hour to train with inexperienced trainers. This is a
very shortsighted business model that will generally attract the wrong kind of clients. The
most effective long-term strategy is to simply charge what you are worth and strive to be
the best at what you do.
SECTION ONE
Anatomy and Physiology
Metabolism
Basic Anatomy and Physiology
Musculoskeletal Anatomy and Physiology
UNIT 1
METABOLISM
TOPICS COVERED IN THIS UNIT
Introduction
Homeostasis
Understanding Metabolism
Metabolic Set Point
Food and Metabolism
Environment and Metabolism
Exercise and Metabolic Responses
Energy Metabolism
ATP Production
Monitoring Metabolism
Conclusion
Unit Outline
I. Introduction
II. Homeostasis
III. Understanding Metabolism
A. Metabolic Set Point
B. Food and Metabolism
C. Environment and Metabolism
D. Exercise and Metabolic Responses
1. Aerobic System Changes
2. Anaerobic System Changes
IV. Energy Metabolism
A. ATP Production
1. ATP/CP Energy Pathway
2. Glycolytic Pathway
3. Oxidative Pathway
4. How the Systems Interact
5. Glycogen Depletion and Metabolism of Fatigue
B. Monitoring Metabolism
V. Conclusion
Learning Objectives
After completing this unit, you will be able to do the following:
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Define key terms.
Understand the role of metabolism in the body and how it relates to exercise.
Determine the metabolic needs of each of the three energy pathways described, and apply
them in the coming units.
INTRODUCTION
As revealed in the book’s introduction, personal fitness trainers have a tremendous
influence on shaping the health and fitness attitudes and practices of those around them.
The sphere of influence includes friends, family members, coworkers, and, of course,
clients. As a fitness professional, your ability to effectively draw your clients into the
fitness lifestyle—including the ability to maintain optimal health—largely depends on your
knowledge of the muscular, cardiopulmonary, and metabolic adaptations to exercise.
These adaptations are known as the training effect.
training effect: An increase in functional capacity of muscles and other bodily tissues as
a result of increased stress (overload) placed upon them.
The training effect impacts the body in several ways. The body begins to change at the
cellular level, allowing more energy to be released with less oxygen. Heart function
improves and the capillaries proliferate in order to allow a more efficient flow of oxygen
and nutrients. The muscles, connective tissues, and bones involved with a particular
physical activity strengthen to accommodate improved proficiency at performing the
activity. Over time, the body’s composition changes (e.g., fat mass may increase while
muscle mass decreases) and movements become more efficient. In addition, resting heart
rate and blood pressure drop. You can help your clients achieve these adaptations by
educating yourself and learning how to develop appropriate fitness and health plans for
them.
homeostasis: The automatic tendency to maintain a relatively constant internal
environment.
The training effect would not be possible without sufficient energy to bring about the
positive muscular, cardiopulmonary, and metabolic adaptations. But where exactly does
this energy come from?
Where Does Energy Come From?
All energy on earth originates from the sun. Plants use the light energy from the sun to
form carbohydrates, fats, and proteins. Carbohydrates are sugars and starches used by the
body as fuel. Fats are compounds that store energy. Proteins are important components of
cells and tissues; they are large, complex molecules comprised of amino acids.
(Carbohydrates, fats, and proteins are discussed in more detail in Section 5 of this text.)
Humans and other animals eat plants and other animals to obtain energy required to
maintain cellular activities. The body uses carbohydrates, fats, and proteins to provide the
necessary energy to maintain cellular activity both at rest and during activity. Because all
cells require energy, the body must have a way to convert carbohydrates, fats, and proteins
into a biologically usable form of energy to both fuel physical activity and provide the
structural components of the body. The ability to run, jump, and lift weights is contingent
upon, and limited by, the body’s ability to transform food into biological energy. These
physical abilities are further contingent upon thousands of chemical reactions that occur
throughout the body all day long. Collectively, these reactions are known as metabolism.
These many chemical reactions occurring in the body must be regulated in order to
maintain a balance. The body consists of trillions of cells, which are organized into tissues,
organs, and systems. This intricate organized system is covered in more detail in Unit 2.
The body’s components work together in a highly organized manner to maintain this
balance. Metabolic activities are continually occurring in the trillions of cells in your body
and must be carefully regulated to maintain a constant internal environment, or steady
state. This steady state must be maintained regardless of your ever-changing external
environment.
HOMEOSTASIS
Homeostasis refers to the body’s automatic tendency to maintain a constant internal
body environment through various processes. Walter Bradford Cannon is credited with
coining the term in his book The Wisdom of the Body (1932). For homeostasis to work,
feedback systems must exist that various physiological functions turn off and on. Imagine
a feedback system such as the thermostat in your furnace or air conditioning system. If the
temperature increases above the set point determined by the system, then the thermostat
shuts off the furnace. In this way, the temperature is kept at the desired steady state. If the
temperature decreases below the set point determined by the system, then the thermostat
turns on the furnace to maintain the desired steady state (see Figure 1.1). This feedback
system revolves around a cycle of events. Information about a change is fed back to the
system so that the regulator (in this example, the thermostat) can control the process (in
the example of temperature regulation).
Figure 1.1 Homeostasis example
A good example of homeostasis in the body is the method by which the body maintains a
constant temperature of 98.6 degrees Fahrenheit. For example, if either physical exertion
or external heat causes your body temperature to rise, your brain sends a signal to increase
the rate of sweating. Heat is carried away in sweat, which evaporates. If body temperature
begins to drop due to a cold external
environment, shivering begins to generate heat and keep the body temperature at that
critical 98.6 degrees F. Other metabolic functions under homeostatic control include the
following:
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Hormone production and concentration level maintenance
Maintenance of serum oxygen levels and carbon dioxide levels
pH balance in the blood and cells
Water content of cells and blood
Blood glucose levels and other nutrient levels in the cell
Metabolic rate
The concept of homeostasis is of special interest to fitness enthusiasts. You are in
equilibrium even with environmental stimuli acting upon you. For example, think about
how your muscles change in response to different training programs. If you spend most of
your time lifting heavy weights, your muscles will grow larger; a shift in your homeostasis
takes place. The simple action of weight training causes more protein synthesis in the
target muscles. Hormone levels change to accommodate this growth. On the other hand, if
you choose to run several miles per day, your muscles will adapt differently. They develop
a higher endurance capacity, they stimulate the formation of more fat-burning, slowtwitch muscle fibers, and they develop a higher capacity to use oxygen in energy
production. Nutrient intake can also affect your homeostatic balance. Eating too much of
the wrong foods or too little of the right foods can cause homeostasis to shift out of
balance. Consume too many calories, and your body stores fat; too little protein, and your
muscles break down. If you don’t consume enough energy-supplying calories, you will feel
tired sooner. For optimum homeostasis and metabolism, eating the right nutrients in the
right amounts at the right times is vital.
UNDERSTANDING METABOLISM
The body sustains itself and adapts to its environment through metabolism. In order for
metabolism to occur, the body needs both energy and building blocks for growth and
repair. It gets its energy from the breakdown of nutrients such as glucose, ketone
bodies, lactic acid, amino acids, and fatty acids. To construct molecules for growth
and repair, a delicate interplay must exist between anabolism and catabolism.
metabolism: The total of all the chemical and physical processes by which the body
builds and maintains itself (anabolism) and by which it breaks down its substances for the
production of energy (catabolism).
glucose: Principal circulating sugar in the blood and the major energy source of the body.
ketone bodies: Bodies produced as intermediate products of fat metabolism.
lactic acid: A by-product of glucose and glycogen metabolism in anaerobic muscle
energetics.
amino acid: The building blocks of protein. There are 24 amino acids, which form
countless number of different proteins.
fatty acids: Any of a large group of monobasic acids, especially those found in animal and
vegetable fats and oils.
anabolism: The building up in the body of complex chemical compounds from simpler
compounds (e.g., proteins from amino acids).
catabolism: The breaking down in the body of complex chemical compounds into
simpler ones (e.g., proteins to amino acids).
The many biochemical processes that make up the body’s metabolism are categorized into
two general phases: anabolism and catabolism. Anabolism and catabolism occur
simultaneously—and constantly. However, they differ in magnitude depending on the level
of activity or rest and on when the last meal was eaten. When anabolism exceeds
catabolism, net growth occurs. When catabolism exceeds anabolism, the body has a net
loss of substances and body tissues and may lose weight.
Anabolism includes the chemical reactions that combine different biomolecules to create
larger, more complex ones. The net result of anabolism is the creation of new cellular
material, such as enzymes, proteins, cell membranes, new cells, and growth/ repair of the
many tissues. That energy is stored as glycogen and/or fat and in muscle tissue. Anabolism
is necessary for growth, maintenance, and repair of tissues.
Catabolism includes the chemical reactions that break down complex biomolecules into
simpler ones for energy production, for recycling of molecular components, or for their
excretion. Catabolism provides the energy needed for transmitting nerve impulses and
muscle contraction.
Metabolism includes only the chemical changes that occur within tissue cells in the body.
It does not include those changes to substances that take place in the digestion of foods in
the gastrointestinal system. For optimal function, a healthy metabolism needs many
nutrients. A slight deficiency of even one vitamin can slow down metabolism and cause
chaos throughout the body. The body builds thousands of enzymes to drive its metabolism
in the direction influenced by activity and nutrition. So, when you are training or engaged
in vigorous physical activity several hours a day, you must ensure that your diet contains
the nutrients your body needs in order to optimize the many metabolic functions taking
place.
METABOLIC SET POINT
Based on the discussion of homeostasis and metabolism, it is evident that the body is a
highly regulated collection of many biochemical reactions. Much research over the years
has revealed that the body seeks to maintain a certain base rate of metabolism, called
the metabolic set point, which results in basal metabolic rate (BMR). This set point
is regulated by both genetic and environmental factors. Researchers have demonstrated
that you can change your metabolic set point through diet and physical activity.
metabolic set point: The base rate of metabolism that the body seeks to maintain;
resulting in basal metabolic rate.
basal metabolic rate (BMR): The minimum energy required to maintain the body’s life
function at rest; usually expressed in calories per hour per square meter of the body
surface.
The metabolic set point is the average rate at which the metabolism runs, and it will result
in a body composition set point. People with a slow metabolism seem to store fat easily,
while people with a fast metabolism seem to be able to eat and never gain fat. Your
metabolic set point can be influenced by the external environment (climate), nutrition,
exercise, and other factors. Studies have demonstrated that when individuals go on a lowcalorie diet, the body’s metabolic set point becomes lower in order to conserve energy. It
actually resets itself to burn fewer calories, thereby conserving energy. Exercise tends to
increase metabolic rate, causing the body to burn more fat for energy.
Calculating Caloric Expenditure
You can estimate your total daily caloric expenditure by multiplying the Harris-Benedict
equations for basal metabolic rate by an activity level factor that accounts for your daily
physical activity levels and the thermic effect of food.
thermic effect: The heat liberated from a particular food; it is a measure of its energy
content and its tendency to be burned as heat. This process of heat liberation is also
commonly referred to as “thermogenesis.”
Eq. 1.1
FOOD AND METABOLISM
In addition to exercise, the type of food you eat can also influence your metabolism. The
food you eat can be burned to liberate energy, it can be converted into body weight, or it
can be excreted. All foods release heat when they are burned. This release of heat is
measured in kilocalories. A calorie is a unit of heat. Practically speaking, this unit is too
small to be useful, therefore, the kilocalorie (1,000 calories) is the preferred unit in
metabolism studies. The term Calorie (with a capital “C”) is synonymous with kilocalorie.
calorie: A unit of heat; specifically, it is the amount of energy required to raise the
temperature of 1 kilogram of water 1 degree Celsius at 1 atmosphere. As a unit of
metabolism (as in diet and energy expenditure), it is spelled with a capital C; 1 Calorie =
1,000 calories, or 1 kilocalorie (kcal).
kilocalorie (kcal): A unit of measurement that equals 1,000 calories, or 1 Calorie. Used
in metabolic studies, it is the amount of heat required to raise the temperature of 1
kilogram of water 1 degree Celsius at a pressure of 1 atmosphere. The term is used in
nutrition to express the fuel (energy) value of food.
The heat liberated from food is known as the thermic effect. Increased thermogenesis
(heat production) correlates with increased oxygen consumption and an increased
metabolic rate. The more heat your body produces, the more oxygen it needs, because heat
cannot be liberated in the absence of oxygen. Food efficiency is simply a measure of how
efficiently a particular food is converted to body weight. Foods with high food efficiency
are prone to be converted to body weight, while foods with low food efficiency are prone to
be burned as energy.
Understanding how the body will use the consumed calories can help you in setting up
your nutritional program. Simply counting calories will not lead to loss of body fat. The
heat liberated from a particular food, whether it is fat, protein, or carbohydrate, is
determined by its particular molecular structure, and this structure determines its thermic
effect. The higher the thermic effect of any particular food, the higher the metabolic rate
will be. Know what the body is consuming; and, more importantly, know how the body
will use the consumed calories. A method of determining the mix of fuels being utilized in
the body is called the respiratory quotient (RQ), which provides a way to measure the
relative amounts of fats, carbohydrates, and proteins being burned for energy.
respiratory quotient (RQ): A method of determining the “fuel mix” being used, giving
us a way to measure the relative amounts of fats, carbohydrates, and proteins being
burned for energy.
The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide expired to the
volume of oxygen consumed. Because the amounts of oxygen used up for the combustion
of fat, carbohydrate, and protein differ, differences in the RQ indicate which nutrient
source is being predominantly used for energy purposes. The formula for calculating RQ is
as follows:
Eq. 1.2
The RQ for carbohydrate is 1.0, whereas the RQ for fat is 0.7. Fat has a lower RQ value
because fatty acids require more oxygen for oxidation than the amount of carbon dioxide
produced. The RQ for energy production from protein is about 0.8. The average person at
rest will have an RQ of about 0.8; however, this result is from using a mixture of fatty acids
and carbohydrates, not the protein itself, for energy production. Remember, proteins
(broken down into amino acids) are not usually used for energy. In a normal diet
containing carbohydrate, fat, and protein, about 40to 45 percent of the energy is derived
from fatty acids, 40 to 45 percent from carbohydrates, and 10 to 15 percent from protein.
However, this rate of energy production varies based on diet, physical activity, and level of
physical training.
oxidation: The chemical act of combining with oxygen or of removing hydrogen.
Research indicates that when the diet is high in carbohydrates, the RQ is higher, therefore
more energy is being produced from carbohydrates. When the diet is low in carbohydrates
and high in fat, more energy is produced from fat. Interestingly, recent studies published
in academic journals suggest that more efficient body fat reduction occurs with a high-fat
diet than with a high-carbohydrate diet (on a calorie-per-calorie basis).
In addition, training intensity affects the energy source during exercise. For example, a
training intensity below 60 percent of maximal oxygen uptake ( O2max) results in a
RQ of about 0.8, indicating an equal portion of energy derived from fatty acids and
carbohydrate. As training intensity increases above 60 percent of O2 max, more
carbohydrate is used for energy. Exercise intensity at 100 percent O2 max (which can
only be sustained for minutes) yields a RQ of 1. Keep in mind that amino acids, in
particular the branched-chain amino acids (BCAAs, which aid in recovery), are also
being used for energy during exercise and at rest, perhaps as much as 10 percent or more
during exercise.
maximal oxygen uptake ( O2 max): The highest rate of oxygen consumption which a
person is capable.
branched-chain amino acids (BCAAs): The amino acids L-leucine, L-isoleucine and
L-valine, which have a particular molecular structure that gives them their name and
comprises 35 percent of muscle tissue. The BCAAs, particularly L-leucine, help increase
work capacity by stimulating production of insulin, the hormone that opens muscle cells to
glucose. BCAAs are burned as fuel during highly intense training and at the end of longdistance events when the body recruits protein for as much as 20 percent of its energy
needs.
In general, physical conditioning lowers the RQ, which means more energy is being
obtained from fatty acids in the trained individual. However, more energy is also being
obtained from protein in the trained individual. Carbohydrate is always being used for
energy. For example, in a study comparing the RQ of untrained versus trained individuals
during exercise, the RQ of the untrained individuals was 0.95 and the RQ of the trained
individuals was 0.9. This means that while both groups were using mostly carbohydrate
for fuel during exercise, the trained individuals were using a higher amount of fatty acids
for energy. At rest, fatty acids are the predominant energy source in most people; as
exercise begins, carbohydrate utilization increases. High-intensity exercise uses more
carbohydrate, while low- to moderate-intensity exercise uses fatty acids and carbohydrate
for energy. Of course, these ratios change when one consumes only fats and proteins and
no carbohydrates as fuel.
While this discussion of RQ is very brief, you can see that the energy substrate utilization
of the body is quite varied, and both composition of the diet and intensity of physical
activity determine which energy substrates are used. Therefore, it is easy to see why
different sports require different dietary considerations.
ENVIRONMENT AND METABOLISM
The body’s environment also influences its metabolic rate. When you are exposed to a
progressively colder climate, your body will increase its metabolic rate to keep the body
temperature constant and to prevent shivering. Shivering is invoked when the core
temperature of the body begins to drop from being in the cold. Shivering is actually a
series of involuntary muscle contractions that are triggered to create heat in the body, like
turning on a furnace. When exposed to higher-than-average cold conditions for a few days,
the body actually increases its basal metabolic rate; its goal is to run hotter than average in
order to compensate for being in a colder climate. When conditions begin to warm up,
even a 60-degree-Fahrenheit (F) day can seem extremely hot, because the body’s
metabolic rate is already running fast. After several days of acclimating to the hot climate,
the metabolic rate decreases and 80 degrees F feels as hot as the 60 degrees F did a few
months earlier.
EXERCISE AND METABOLIC RESPONSES
Exercise stimulates a series of metabolic responses that affect the body’s anatomy,
physiology, and biochemical makeup.
Endurance exercise stimulates the following changes:

Increased muscle glycogen storage capacity
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Increased muscle mitochondrial density
Increased resting adenosine triphosphate (ATP) content in muscles
Increased resting creatine phosphate (CP) content in muscles
Increased resting creatine content in muscles
Increased aerobic enzymes
Increased percentage of slow-twitch muscle fibers
Decreased percentage of fast-twitch muscle fibers
Decreased muscle size, when compared to strength training
Increased cardiac output
Decreased resting heart rate
Decreased body fat
Increased Krebs cycle enzymes
Increased number of capillaries
The magnitude of these changes is driven primarily by whether the exercise is anaerobic or
aerobic. The type and duration of exercise dictates the primary energy mix used. Highintensity exercise simulates development of fast-twitch muscle fibers, while low-intensity
exercise results in development of slow-twitch muscle fibers.
In addition, a series of hormonal changes occur during exercise and non-exercise periods.
These changes also are benefited and facilitated with a nutrient profile that matches the
type of metabolic fluctuation.
Aerobic System Changes
Aerobic training greatly increases the body’s functional capacity to transport and use
oxygen and to burn fatty acids during exercise. Recent research shows that long, slow
distance training is not as efficient as interval training in facilitating this functional
capacity. Some of the major changes measured as a result of aerobic exercise (especially
interval training) include the following:
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Increased mitochondrial density in slow-twitch muscle fiber, which results in higher
energy production from fatty acids. Maximum oxidative capacity develops in all fiber types
Higher aerobic capacity
Increase in trained muscle capacity to utilize and mobilize fat, resulting from higher
amounts of fat-metabolizing enzymes, and increased blood flow
Greater development of slow-twitch muscle fibers, increased myoglobin content (an iron–
protein compound in muscle), which acts to store and transport oxygen in the muscles
Anaerobic System Changes
Anaerobic training greatly increases the body’s functional capacity for development of
explosive strength and maximization of short-term energy systems. Some of the major
changes measured as a result of anaerobic exercise include the following:
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Increased size and number of fast-twitch muscle fibers
Increased tolerance to higher levels of blood lactate
Increases in enzymes involved in the anaerobic phase of glucose breakdown (glycolysis)
Increased muscle resting levels of ATP, CP, creatine, and glycogen content
Increased levels of growth hormone and testosterone after short bouts (45 to 75 min) of
high-intensity weight training
adenosine triphosphate (ATP): An organic compound found in muscle which, upon
being broken down enzymatically, yields energy for muscle contraction.
creatine phosphate (CP): A high-energy phosphate molecule that is stored in cells and
can be used to immediately resynthesize ATP.
ENERGY METABOLISM
Energy metabolism is a series of chemical reactions that result in the breakdown of
foodstuffs (carbohydrate, fat, protein) by which energy is produced, used, and given off as
heat. Roughly, the body is about 20 percent efficient at trapping energy released. About 80
percent is released as heat, which explains why your body heats up quickly when you
exercise. A closer look at muscle anatomy reveals that the mode of energy storage and
energy systems used is related to physical activity.
Physical activities can be classified into these four basic groups, based on the energy
systems that are used to support these activities:
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Strength/power: Energy coming from immediate ATP stores. Examples include shot
put, powerlift, high jump, golf swing, tennis serve, and a throw. Activities last about 0 to 3
seconds of maximal effort.
Sustained power: Energy coming from immediate ATP and CP stores. Examples include
sprints, fast breaks, football lineman. Activities last about 0 to 10 seconds of near-maximal
effort.
Anaerobic power/endurance: Energy coming from ATP, CP, and lactic acid. Examples
include 200- to 400-meter dash and 100-yard swim. Activities lasting about 1 to 2
minutes.
Aerobic endurance: Energy coming from the oxidative pathway. Activities last over 2
minutes.
In power events, which last a few seconds or less at maximal effort, the muscles depend on
the immediate energy system, namely ATP and CP reserves. In speed events, the
immediate and non-oxidative (glycolytic) energy sources are utilized. In endurance events,
the immediate and non-oxidative energy sources are used, and the oxidative energy
mechanisms become a more important source of energy. ATP and CP are replenished from
energy derived from complete breakdown of glucose, fatty acids, and some proteins.
ATP PRODUCTION
Adenosine triphosphate (ATP) is the molecule that stores energy in a form that can be
used for muscle contractions. Energy production then revolves around rebuilding ATP
molecules after they are broken down for energy utilization. Muscle cells store a limited
amount of ATP. During exercise the body requires a constant supply of ATP in
order to provide the energy needed for muscular contraction. Therefore, to maintain a
constant supply of energy, metabolic pathways must exist in the cell with the ability to
produce ATP rapidly. Muscle cells can produce ATP by any one of or a combination of
three metabolic pathways: the ATP/CP pathway, the glycolytic pathway, and the oxidative
pathway.
ATP/CP Energy Pathway
Creatine phosphate (CP) is high-energy phosphate molecule that is stored in cells and can
be used to immediately re-synthesize ATP. The ATP/CP pathway(see Figure 1.2) is
anaerobic, which means it requires no oxygen for energy use. This energy pathway is
demonstrated in sports that require ballistic, explosive strength or maximal effort for short
periods of time, such as shot putting, pitching, weight lifting, and powerlifting.
ATP/CP pathway: ATP and CP provide anaerobic sources of phosphate-bond energy.
The energy liberated from hydrolysis (splitting) of CP re-bonds ADP and Pi to form ATP.
ATP is the energy source for all human movement. The release of one of its three
phosphate molecules provides the energy for human movement. Unfortunately, muscle
cells store only a limited supply of ATP that is readily available for use (5 mmol/kg of
muscle). In maximal efforts, it is totally gone within 1.26 seconds! However, regardless of
their intensity or length, all activities begin with this pathway. With the help of an enzyme
called myosin ATPase, ATP loses one phosphate molecule in order to release energy (see
Equation 1.3).
Eq. 1.3
Figure 1.2 The ATP/CP energy pathway
For short-term, high-intensity activities such as shot putting or throwing, this pathway is
enough. However, further use in this pathway requires that theadenosine
diphosphate (ADP; di = the two phosphate molecules left after one is lost) be resynthesized back to ATP with the help of creatine phosphate (CP) and an enzyme called
creatine kinase (see Equation 1.4).
adenosine diphosphate (ADP): an organic compound in metabolism that functions in
the transfer of energy during the catabolism of glucose, formed by the removal of a
phosphate molecule from adenosine triphosphate (ATP) and composed of adenine, ribose,
and two phosphate groups.
Eq. 1.4
Like ATP, CP is stored in small amounts (16 mmols/kg of muscle). As seen in Figure 1.3,
CP stores fall rapidly after 10 seconds of maximal activity and are usually completely
depleted in under 60 seconds.
Whether or not you can increase your resting levels of ATP through training has not widely
been studied or understood. Research has suggested that it is possible through both weight
training and aerobic training. However, this possibility is mainly because of fiber
hypertrophy (increase in size), thus more ATP can be stored in type II than in type I
muscle fibers (considering the size and growth potential of type II fibers).
type II muscle fibers (fast twitch): Muscle fiber type that contracts quickly and is
used mostly in intensive, short-duration exercises.
type I muscle fibers (slow twitch): A muscle fiber characterized by its slow speed of
contraction and a high capacity for aerobic glycolysis.
Perhaps an even bigger question than “how much?” or “can you increase?” is “how quickly
can ATP and CP stores be replenished?” Although individual differences exist, research
has shown that ATP stores can be fully restored within 3.5 minutes and CP stores can be
fully replenished within 8 minutes.
Figure 1.3 Pathways of muscular energetics
Glycolytic Pathway
Like the ATP/CP pathway, the glycolytic pathway is anaerobic. Once it has depleted the
readily available ATP/CP stores, the body must break down carbohydrates to produce
more ATP. This process uses either glycogen (which is stored in the muscle cells) or
glucose (which is found in the blood) to convert ADP back into ATP; the waste product is
lactic acid (see Equation 1.5).
glycolytic pathway: A metabolic process in which glucose is broken down to produce
energy anaerobically.
Eq. 1.5
This lactic acid eventually builds more quickly than it can be flushed out of the muscle to
the point of the anaerobic threshold, otherwise known as muscular fatigue. At this point,
the body must either stop or slow down until the lactic acid is removed. Lactic acid is
converted to a less toxic form, called lactate, which is used either as an energy substrate or
to produce more glucose (a process called gluconeogenesis). Getting rid of lactic acid is
not as important as it is how efficiently the body can use it. If you produce lactic acid faster
than you can use it, therein lies the problem. Stored sugars are rarely ever depleted (and
are never depleted in the glycolytic pathway). However, this is not the limiting factor; the
limiting factor is the accumulation of lactic acid. Generally, the glycolytic pathway ends
under maximal conditions at around 80 seconds before the oxidative pathway (and lower
levels of activity) takes over.
gluconeogenesis: Chemical process that converts lactate and pyruvate back into
glucose. When glycogen (sugar stored in muscles) stores are low, glucose for emergency
energy is synthesized from protein and the glycerol portion of fat molecules. This is one
important reason that ATP/CP athletes and glycolytic athletes are warned to stay away
from undue aerobic exercise: It’s muscle-wasting.
How well muscles function in the glycolytic pathway is determined by three related
factors:
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How quickly the body can utilize the lactic acid
How well the body can tolerate the pain caused by the accumulation of lactic acid
How far the body can go before it becomes vital to clear the lactic acid in order for work to
continue. This is called the anaerobic threshold.
Blood lactate levels usually return to normal within an hour after activity. Research shows
that training can increase the rate in which lactic acid is utilized or removed as well as
push back the anaerobic threshold. As for the ability to tolerate the pain, it comes with
personal experience.
anaerobic threshold: The point where increasing energy demands of exercise cannot be
met by the use of oxygen, and an oxygen debt begins to be incurred.
Oxidative Pathway
The oxidative pathway is a system that is aerobic, which means it uses oxygen to
produce ATP by way of the Krebs cycle and electron transport chain. Ultimately,
more ATP is produced through this pathway than through the other two; however, it takes
much longer. Pyruvate, which is produced through glycolysis, undergoes a long trip
through the Krebs cycle to convert several coenzymes that have lost an electron back into
their original state. It is in the electron transport chain where these coenzymes undergo
oxidation to convert ADP back into ATP. In the end, up to 38 molecules of ATP can be
produced through the oxidative pathway.
oxidative pathway: A metabolic process in which oxygen combines with lactic acid,
resynthesizing glycogen to produce energy aerobically.
Krebs cycle: Citric acid cycle; a set of 8 reactions, arranged in a cycle, in which free
energy is recovered in the form of ATP.
electron transport chain: The passing of electrons over a membrane, aiding in a
reaction to recover free energy for the synthesis of ATP.
pyruvate: A byproduct of glycolysis.
It is only in this pathway that fat can be used for energy. Breaking down fat for energy is
also a long process (called beta oxidation), which does not directly produce ATP.
beta oxidation: A series of reactions in which fatty acids are broken down.
Rather, it provides the coenzymes needed for the Krebs cycle. Scientists have estimated
that while at rest (and in the oxidative pathway), 70 percent of energy comes from
fat, not carbohydrates or protein. However, as exercise intensity increases, more and more
carbohydrates are used instead of fat (beta oxidation can’t keep up). In fact, at the upper
limits of the aerobic pathway, 100 percent of the energy is coming from carbohydrates—
not fat! If at these levels carbohydrates aren’t available, the body will indeed catabolize the
very muscle it’s using for energy.
How the Systems Interact
To better understand how each of these energy systems relate to each other, you need to
take a look at what happens when muscles contract. First, consider the immediate energy
systems. The brain sends a signal along the nerves, triggering a release of calcium ions in
the muscles, which stimulates the muscles to contract and, in the process, the high-energy
molecule ATP releases energy and is reduced to ADP plus one phosphate
Figure 1.4 Pathway interactions
atom. In this way, the immediately available ATP stores are depleted very rapidly, in the
first few seconds of a maximal muscle contraction.
The second immediate source of cellular energy is creatine phosphate (CP). The cell
contains several more times CP molecules than ATP molecules. Creatine phosphate serves
to instantaneously regenerate ATP molecules. Therefore, the ATP that is broken down to
ADP during muscle contraction is restored to the high-energy ATP by CP. The third
immediate energy system enables the cell to regenerate ATP from two ADP molecules,
resulting in one ATP and one adenosine monophosphate (AMP) molecule. This immediate
energy source is depleted in a matter of seconds under conditions of all-out effort
(maximal muscle contractions).
The storage capacity of ATP and CP in a cell is quickly reached for a particular muscle size.
In order to increase the amount of ATP and CP on hand, the muscle fibers must increase
in size. This is why power athletes get big muscles. The workload demands that more ATP
and CP be available. To meet this demand, the muscle fibers increase in size, causing the
entire muscle to get big. When you train, different energy systems are conditioned to work
best at the particular workload imposed on the muscles.
As the immediate energy supply is quickly depleted through high-intensity physical
activity, the non-oxidative energy source kicks in. The non-oxidative system is a major
contributor of energy during 4 to 50 seconds of effort. Non-oxidative metabolism
(glycolysis) involves the breakdown of glucose to regenerate ADP into ATP. Muscle tissue
is densely packed with non-oxidative enzyme systems. What happens chemically is that
the glucose molecule is split in half and energy is released. This energy is enough to
regenerate 2 ATP molecules and leave two pyruvate molecules. In general, these pyruvate
molecules are immediately converted to lactic acid molecules. The amount of free glucose
is generally low in the cells, so glucose is derived from the breakdown of glycogen.
Fast-twitch muscle fibers (those associated with strength and size) are also referred to as
fast glycolytic muscle fibers, because they house the metabolic machinery to get quick
energy through fast glycolysis pathways. The fast-twitch fibers have a low capacity for
oxidative metabolism and are instead set up to run glucose through their fast glycolysis
pathways. Lactic acid then builds up because it is being produced too rapidly to enter into
the oxidative pathways. Lactic acid is then cleared from the muscle, fed into the
bloodstream, taken to the liver, and there made into glucose and glycogen. Glycolysis takes
place in the cytoplasm of the cell.
For physical activities lasting more than 2 minutes, the oxidative metabolic pathways
produce the majority of energy to maintain muscle contractions. Potential oxidative
energy sources include glucose, glycogen, fats, and amino acids. Oxidative energy
production takes place in the mitochondria of the cells. Far more energy is produced when
glucose is completely broken down in the mitochondria. Glucose is still first split in half by
glycolysis. The pyruvate molecules then enter into the mitochondria, where they are
completely broken down. The oxidative pathways are the Krebs cycle and electron
transport. Fatty acids, which come from fat, are a major energy source during endurance
events. The processes of fat utilization are activated more slowly than carbohydrate
metabolism and proceed at a lower rate. Fatty acids are activated and combined with the
molecule carnitine, which enables them to then be transported into the mitochondria.
Glycogen Depletion and Metabolism of Fatigue
Glycogen is essential to performance for both anaerobic and aerobic activities. Muscles
being strenuously exercised will rely on glycogen to power these strength-generating
muscle contractions. In endurance exercise, while the primary fuel is fatty acids, glycogen
is also utilized. In fact, fat catabolism works better when carbohydrates are being
metabolized. Studies on long-term exercise and work performance all indicate the onset of
fatigue when glycogen is depleted. This again underscores the importance of adequate
carbohydrate intake and glycogen replenishment. Glycogen depletion is just one factor
that contributes to the onset of fatigue. Several other fatigue-causing factors facing
athletes include the following:
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ATP and CP depletion
Lactic acid accumulation
Calcium ion buildup in muscles
Oxygen depletion
Blood pH decrease
MONITORING METABOLISM
Until recently, there were no affordable and easy-to-use home testing methods that were
designed for athletes to measure key metabolic parameters. Measuring the state of
nitrogen metabolism allows you to determine whether protein intake is sufficient and also
whether certain supplements are being ingested in amounts that are sufficient for
improving nitrogen balance. Currently on the horizon is a newly developed testing device
that combines nitrogen balance testing with fat metabolism status. These tests measure
the output of metabolic waste products in urine. They are easy to use and offer a means to
finely tune your training and nutrition programs.
A product developed by B. Fritz and Dr. Fahey is a testing method that was probably the
best-kept secret of Russian athletes. This test provides an economical way to determine
testosterone and cortisol levels in the body by analysis of saliva. When the body is over
trained, cortisol levels increase. Cortisol is a catabolic hormone that stimulates the
breakdown of muscle tissue. High amounts in the blood ultimately lead to tissue wasting
and negative nitrogen balance. So, when the testosterone/cortisol ratio is high, anabolism
is prevailing. However, when cortisol levels are high and the ratio is lowered, it is an
indication of overtraining. Testing testosterone/cortisol
ratio helps you determine whether the body is in a state of overtraining or not. In this way,
you can determine how hard to train, whether to take a few days off, or if training intensity
should increase.
In addition, in the medical field and in many fitness centers, handheld portable indirect
calorimeters are used that measure oxygen consumption ( O2) and determine resting
metabolic rate (RMR). As discussed earlier in this unit, the rate of oxidation or the
burning of the calories is different for fat, carbohydrate, and protein. The food you eat can
either be burned to liberate energy, converted into body weight, or be excreted. If you light
a candle and then place a dome over the candle, cutting off the fire’s source of oxygen, the
fire will go out. In the same way the body’s ability to undergo oxidation is contingent on
oxygen. If the body is getting more oxygen, it should be burning more calories.
resting metabolic rate (RMR): The amount of energy (calories) required to efficiently
perform vital bodily functions such as respiration, organ function and heart rate while the
body is awake, but at rest.
Nutrition monitoring plays a vital role in the care of patients with diabetes, heart disease,
high blood pressure, and obesity, as well as conditions that place patients at risk for
malnutrition, such as cancer, burns, trauma, infection, obstructive lung disease, and HIV.
Indirect calorimeters can be used in acute care, long-term care, home care, and clinic-
based care settings such as physician offices, rehabilitation centers, ambulatory surgery
centers, and fitness-based facilities.
CONCLUSION
In order to maintain its many chemical and physical activities, the body needs energy.
Earth’s energy originates from the sun. Plants use solar energy to perform chemical
reactions to form carbohydrates, fat, and protein. Humans, like other animals, consume
plants and other animals to obtain the energy required to maintain cellular activities.
These cellular activities, known as metabolism, are maintained under homeostatic
controls. The many chemical reactions occurring in the body must be regulated in order to
maintain a balance between the trillions of cells in the body. These cells maintain balance
through an intricate organization system. We will now discuss this intricate organized
system known as the body.
Received
Key Terms
adenosine diphosphate (ADP)
adenosine triphosphate (ATP)
amino acid
anabolism
anaerobic threshold
ATP/CP pathway
basal metabolic rate (BMR)
beta oxidation
branched-chain amino acids (BCAAs)
calorie
catabolism
creatine phosphate (CP)
electron transport chain
fatty acids
gluconeogenesis
glucose
glycolytic pathway
homeostasis
ketone bodies
kilocalorie (kcal)
Krebs cycle
lactic acid
maximal oxygen uptake ( O2 max)
metabolic set point
metabolism
oxidation
oxidative pathway
pyruvate
respiratory quotient (RQ)
resting metabolic rate (RMR)
thermic effect
training effect
type I muscle fibers (slow twitch)
type II muscle fibers (fast twitch)
Unit Summary
In order to maintain its many chemical and physical activities, the body needs energy. All
Earth’s energy comes from the sun. Plants use solar energy to perform chemical reactions
to form carbohydrates, fats, and protein. Humans like animals consume plants and other
animals to obtain the energy required to maintain cellular activities.
The body’s systems work together in a highly organized manner to maintain a balance,
which is known as homeostasis.
A. Metabolism can be defined as all of the chemical processes that occur in the body.
Metabolism is categorized into two general phases; anabolism (building phase) and
catabolism (breaking down phase).
B. The food you eat can either be burned to liberate energy, converted into body weight, or
excreted.
C. The calories coming from protein are used for maintenance, repair, and growth of new
tissues and organs. Calories from carbohydrates are used for energy. Calories from
conventional sources of a fat are prone to be stored as fat since it already has the same
molecular structure as body fat.
D. Energy metabolism is a series of chemical reactions that result in the breakdown of
foodstuffs (carbohydrate, fat, protein) by which energy is produced, used, and given off as
heat.
E. Adenosine triphosphate (ATP) is the molecule that stores energy in a form that can be
used for muscle contractions.
F. Muscle cells can produce ATP by any one or a combination of three metabolic pathways:
the ATP/CP pathway, glycolytic pathway, and oxidative pathway.
G. The formation of ATP without oxygen is known as anaerobic metabolism. This includes
the ATP/CP and the anaerobic glycolytic pathway. Short-term activities at higher
intensities utilize ATP production from anaerobic energy pathways.
H. In the ATP/CP system, the phosphate (P) is separated from the creatine (C) and
combines with adenosine diphosphate (ADP) to reform ATP. One molecule of CP results in
the reformation of 1 molecule of ATP. This system is sufficient for 3 to 15 seconds of ATP
production.
I. In non-oxidative glycolysis, glucose or glycogen is converted to lactic acid. One molecule
of glucose results in 2 molecules of ATP and 1 molecule of glycogen results in 3 molecules
of ATP. This system is reliable for 1 to 2 minutes of maximal effort.
J. The formation of ATP with oxygen is known as aerobic metabolism. This includes the
aerobic glycolytic pathway and the oxidative pathway. Long-term activities with a low to
moderate intensity utilize ATP production from aerobic sources.
K. The aerobic metabolism of 1 molecule of glucose results in the production of 38
molecules of ATP and 1 molecule of glycogen results in the production of 39 ATP.
L. Glycogen is essential for both anaerobic and aerobic activities. Muscles being
strenuously exercised rely on glycogen to power strength-generating muscle contractions.
In endurance exercise, while the primary fuel is fatty acids, glycogen is also utilized.
M. Monitoring metabolism is possible through nitrogen test sticks or handheld, portable,
indirect calorimeters.
UNIT 2
BASIC ANATOMY AND PHYSIOLOGY
TOPICS COVERED IN THIS UNIT
Levels of Organization in the Human Body
Cells
Tissues
Systems of the Body
Conclusion
Unit Outline
I. Levels of Organization in the Human Body
A. Cells
1. Plasma Membrane
2. Nucleus
3. Ribosomes
4. Endoplasmic Reticulum (ER)
5. Golgi Apparatus
6. Lysosomes
7. Mitochondria
B. Tissues
1. Epithelial Tissue
2. Connective Tissue
3. Muscle Tissue
4. Nervous Tissue
C. Systems of the Body
1. Respiratory System
2. Circulatory System
a. Anatomy of Blood
b. How Respiratory and Circulatory Interaction Works
c. Heart
i. Heart Tissue
ii. Heart Rate
iii. Stroke Volume
3. Digestive System
a. Physical Components
i. Mouth
ii. Esophagus
iii. Stomach
iv. Small Intestine
v. Large Intestine and Rectum
vi. Pancreas
vii. Liver and Gallbladder
b. Factors Affecting Digestion
4. Nervous System
a. Organization of the Nervous System
b. Neural Adaptations: The Mind–Body Link
5. Endocrine System
a. Importance of Hormones
b. Types and Functions of Hormones
c. Hormones and Blood Sugar Regulation
i. Insulin
ii. Glucagon
d. Muscle Growth and Hormonal Regulation
i. Growth Hormone
ii. Thyroid Hormones
iii. Adrenal Hormones
II. Conclusion
Learning Objectives
After completing this unit, you will be able to do the following:
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Define and describe key terms.
Know the elemental structure and function of each system of the body.
Describe the effects that training has on each system of the body.
Understand the importance of the mind–body link.
LEVELS OF ORGANIZATION IN THE HUMAN BODY
The principal systems of the human body interact with each other to create what is known
as the training effect. These principal systems are part of an intricate, multi–level
organizational structure. The simplest level is the chemical level. The smallest amount of a
chemical element is the atom. Atoms can combine to form molecules. About 98 percent of
the human body is composed of only six elements: oxygen, carbon, hydrogen, nitrogen,
calcium, and phosphorous. The next level is the cellular level. Atoms and molecules bind
to form the building blocks of the body. Each cell consists of specialized cell parts called
organelles. The nucleus, which is the control center of the cell, is an organelle. The next
level of organization is the tissue level. A tissue is a group of closely related cells
specialized to perform a specific function. The four main tissues in the body are muscle
tissue, nervous tissue, connective tissue, and epithelial tissue. These tissues are then
organized into organs such as the heart or brain. The organs and tissues work together to
perform specific functions of the body’s systems. These body systems make up the human
body.
tissue: A collection of similar cells and their intracellular substances.
Figure 2.1 Levels of organization in the human body
Figure 2.2 Cellular components
CELLS
Just as every molecule has building blocks, so do tissues and structures. Cells form the
fundamental units of life. Together they somehow organize themselves into the human
body. The human body is composed of an estimated 100 trillion cells of various forms and
functions. Striated muscle cells can be several inches long and have the unique ability to
shorten in length, thereby causing muscle contractions. Fat cells are small and round in
shape and function to store fatty acids for energy needs during lean times.
Another magnificent characteristic of cells is that they can reproduce themselves. In fact,
cells can only arise from preexisting cells. The complex human body originates from the
union of two existing cells: the female egg and the male sperm. These sex cells merge to
form one larger cell called the zygote, which is the starting point of a multi-trillion-celled
human body. The zygote divides and forms two cells. (Sometimes, these two zygote cells
become separated and develop independently of each other, forming twins.) The two
zygote cells continue to divide and form four cells. This process continues forever. Even
when the total number of cells reaches a relatively fixed amount, cells continue to divide to
replace old or dead cells. Throughout life, cells are continually dying and reproducing.
Each type of cell has its own anatomy and physiology. Specialized subcellular structures,
called organelles, perform specific functions. Each cell typically contains the following
organelles.
Plasma Membrane
Picture the cell as an inflated balloon. The outer boundary is called the plasma membrane,
or cell membrane. It is a complex structure made up of mostly proteins and a phospholipid
bilayer. The phospholipid bilayer (which is
made up of glycerol, two fatty acids, and a phosphate group) forms a double-walled
balloon-like structure with proteins embedded in these bilayer sheets. The nutritional
significance of this structure is that the cell membrane is made up of fatty acids, which are
part of the phospholipid bilayer. For this reason, fats are an important part of the diet.
And while we need to make sure we do not eat too much of it, we do need an appropriate
amount to serve the essential building blocks for all cells. Fats are especially important for
athletes who are training to gain muscle mass and for long distance athletes whose
metabolisms burn up a tremendous amount of fatty acids. (Fats consist mainly of three
fatty acids attached to the three carbon glycerol molecules; thus the name triglycerides.)
fatty acid: Any of a large group of monobasic acids, especially those found in animal and
vegetable fats and oils.
triglycerides: The storage form of fat made up of three fatty acids and a glycerol group.
The plasma membrane can selectively allow the transport of molecules through it and also
actively transport certain compounds across it through special mechanisms. It is therefore
referred to as a semipermeable plasma membrane. This semipermeability gives the cell
control over the type and amount of a substance it allows inside. In addition, the cell can
rid itself of undesirable compounds while retaining desirable ones. Insulin is an
important hormone that is responsible for stimulating the uptake of glucose and amino
acids across the plasma membrane. Insulin levels increase in the body after a meal to
ensure that these vital nutrients get into the cells. You can maximize the function of
insulin through supplementation and timing of meals in relation to training.
insulin: A polypeptide hormone functioning in the regulation of the metabolism of
carbohydrates and fats, especially the conversion of glucose to glycogen, which lowers the
blood glucose level.
glucose: Principal circulating sugar in the blood and the major energy source of the body.
Nucleus
Commonly called the control center of the cell, the nucleus was first discovered in 1830;
discovery is credited to the scientist Robert Brown. Usually, the nucleus is situated in
approximately the center of each cell and is slightly darker than the surrounding
cytoplasm. The nucleus is essentially a cell within a cell, which has a membrane of its own
and houses genetic material.
THE NUCLEUS HOUSES THE DEOXYRIBONUCLEIC ACID (DNA) OF THE
CELL. Strands of DNA form chromosomes. The human cell contains 46 chromosomes—
23 matching pairs. Each parent contributes one set of chromosomes from sex cells; 23
come from the sperm and 23 come from the egg. Chromosomes contain the blueprint for
all genetic traits, including eye color, hairline shape, and even predisposition to allergies,
among many others. Chromosomes are suspended in a liquid called the nucleoplasm. The
liquid between the plasma membrane and nuclear membrane is called cytoplasm, or
cytosol.
The nucleus typically functions to initiate production of substances needed by the cell. The
process is initiated by an intracellular (within the cell) signal, which causes specific genes
on certain chromosomes to produce exact copies of the gene sequence being activated.
These pieces of material carrying genetic information are called messenger ribonucleic
acid (RNA). The information contained on the messenger RNA strands may be the
sequence of amino acids needed for a protein molecule, such as insulin. The messenger
RNA is then transported from the nucleus, through pores in the nuclear membrane, and
on to the cytoplasm. Once in the cytoplasm of the cell, the strand of messenger RNA is
used as a template to make molecules in the cytoplasm. For this event to occur, ribosomes
must be connected to the messenger RNA strand. Ribosomes are also organelles and they
run along the messenger RNA strands while in the cytoplasm. As the ribosomes go along
the messenger RNA strand, they function to connect each code point along the RNA to the
corresponding transfer RNA which has an amino acid attached to it. The ribosomes roll
along the messenger RNA, recruiting amino acids to produce proteins. If certain amino
acids are missing, the protein chains cannot be completed; protein synthesis can be
reduced or temporarily stopped. This is why adequate and effective protein intake is
mandatory for human activity. This concept of the limiting nutrient is important to
consider. The diet can be abundant in calories But if an essential nutrient is in short
supply, it can limit certain reactions needed for the cell—and therefore the active person—
to thrive.
The nucleus has another important function: It initiates cell division. During cell division,
each chromosome must duplicate itself so that the new cell will contain a full set of 23
pairs of chromosomes.
Ribosomes
Ribosomes are extremely small, spherical organelles made up of protein and RNA. They
are the most numerous of cell organelles. They are found scattered throughout the cell’s
cytoplasm and also along the surface of another organelle, the endoplasmic reticulum
(discussed next). Ribosomes function in pairs as two subunits; one subunit is smaller than
the other. Ribosomes are located in the cytoplasm and make various compounds from
messenger RNA for local cellular needs. Ribosomes situated on the endoplasmic reticulum
synthesize compounds for use outside the cell and can be channeled out of the cell for
export, such as with hormones and digestive enzymes.
Endoplasmic Reticulum (ER)
This organelle forms a network of intracellular canals within the cytoplasm. It exists in two
forms: rough ER and smooth ER. Rough ER is ER with ribosomes attached. Here is where
proteins and other biomolecules can be made and transported through the ER’s canal
network to other parts of the cell and outside the cell. Smooth ER is without ribosomes
and its function is less clear, although it appears that smooth ER may be the site of steroid
synthesis in the testes and adrenal glands. Evidence also indicates that lipid and
cholesterol metabolism occur in smooth ER of the liver cells.
Golgi Apparatus
The Golgi apparatus consists of stacks of tiny oblong sacs embedded in the cytoplasm of
the cell near the nucleus. Research has presented convincing evidence that the Golgi sacs
are responsible for synthesis of carbohydrate biomolecules (Cooper, 2000). These
carbohydrates are then combined with the proteins made in the ER to form glycoproteins.
Glycoproteins play an important part in the function of enzymes, hormones, antibodies,
and structural proteins, among other things. As the amount of glycoprotein produced
within the Golgi sac increases, the sac becomes inflated. At this point, small spheres form
along the surface of the Golgi sac and break away. These globules contain the
glycoproteins, which are transported to the cell membrane and then out of the cell into the
bloodstream to be used by other cells.
Lysosomes
Lysosomes are other sac-like structures whose size and shape change with the degree of
their activity. They start out small, and as they become active, they increase in size.
Lysosomes contain a variety of enzymes, which act as catalysts, directing all major
biochemical reactions. These enzymes are capable of breaking down all of the main
components of the cell, such as protein, fat, and nucleic acid. The broken-down products
formed inside the lysosome can be used as raw materials for synthesis of new biomolecules
or for energy. In this way, lysosomes serve to contain and isolate these important cellular
digestive enzymes and thereby prevent complete digestion of the cell. They also play a
limited role in the engulfing and destroying of bacteria that may enter the cell.
Mitochondria
After the nucleus, mitochondria are probably the most known and talked about organelle
in the athletic arena, due to their role in the generation of energy. Referred to as
the powerhouse of the cell, mitochondria are small, complex organelles that resemble a
sausage in shape. They consist of a smooth outer membrane, which surrounds an inner
membrane, forming a sac within a sac. The inner membrane is folded like an accordion,
and it forms a number of inward extensions called cristae.
The enzymes that are essential for making one of the most important biomolecules,
adenosine triphosphate (ATP), exist in the mitochondria. It is here in the mitochondria
that ATP stores energy which is used to power biological functions. (More will be said
about ATP in the units to follow.) Within the inner mitochondria membrane, catabolic
enzymes (which are involved in breaking down of biomolecules) catalyze reactions that
provide the cells with life-sustaining energy.
Nutrients such as glucose and fatty acids are made of carbon atoms linked together with
chemical bonds. When these chemical bonds are broken, energy is released. Within the
intricate confines of the mitochondria, this energy can be trapped and stored in the ATP
molecule,
which can then make use of it. In other words, the energy from glucose is transferred to
the ATP molecule, and the energy is now in a form that the body can use.
These biological structures are the main components of the cell. Some of the other
structures include glycogen granules, which store glycogen and enzymes for glycogen
breakdown and synthesis. Although not a structure, the cytoplasm is worth mentioning.
This liquid portion of the cell is the site of many reactions,
including gluconeogenesis (glucose and glycogen formation), fatty acid synthesis,
activation of amino acids, and glycolysis (the first phase of breaking down glucose to
make ATP molecules for energy).
glycogen granule: Structure of the cell that stores glycogen and enzymes for glycogen
breakdown and synthesis.
gluconeogenesis: Chemical process that converts lactate and pyruvate back into
glucose.
glycolysis: The metabolic process that creates energy from the splitting of glucose to
form pyruvic acid or lactic acid and ATP.
TISSUES
While the cell is the fundamental unit of life, tissues are the fundamental units of function
and structure for the human body. Tissues are defined as the aggregation of cells bound
together working to perform a common function. For example, cells of the adrenal cortex
form a glandular tissue that produces several hormones, including androgens,
glucocorticoids, and mineralocorticoids. Muscle tissue is made up of special muscle fiber
cells that collectively have the ability to shorten and form the basis of contractile tissue.
This section introduces you to the basic tissues that make up the body. The human body is
considerably complex, yet the tissues that form it can be separated into four basic groups:
epithelial, connective, muscle and nervous tissue.
Epithelial Tissue
Epithelial tissue is found throughout the body: as a continuous external layer over the
whole body (skin), on most of the body’s inner cavities, and making up the body’s several
glands. On the surface, epithelial tissue functions to protect underlying cells from bacterial
invasion, adverse chemicals, and drying. On the inside, it functions as
Figure 2.3 Human skin
absorbing and secreting tissue, such as in digestive system glands. Epithelial tissue is
divided into four groups, which are distinguished according to the shape of the cells that
comprise them. They are as follows:
1. Squamous epithelium is composed of one layer of flat cells. It is located in the linings
of the mouth, esophagus, and blood and lymphatic vessels. Substances can easily diffuse
through this layer of cells.
2. Cuboidal epithelium is made of cube-shaped cells as found in the lining of kidney
tubules.
3. Columnar epithelium resembles a column or pillar in shape. These cells are
widespread throughout the body, forming linings in the digestive and respiratory tracts.
They function as secretory cells or absorptive cells. Some also have small hairs, called cilia,
which beat rhythmically and move materials out of a passage, as in the respiratory tract
where cilia serve to sweep out foreign matter that may pass into the lungs.
4. Glandular epithelial cells secrete mucus and hormones, such as those of the salivary
and thymus glands.
Connective Tissue
Connective tissue is widespread in the body. It serves to connect structures and provide
support. For example, connective tissue joins other tissues to each other, muscles to bone,
and bone to bone. Connective tissue is composed of cells embedded in a nonliving matrix.
The nature of the matrix, rather than that of the cells themselves, determines the function
of a particular type of connective tissue. Connective tissue consists predominantly of
intercellular material interspersed among relatively few cells. Blood is also considered a
connective tissue because it consists of a fluid matrix with cells suspended within.
Some types of connective tissue have the consistency of soft gels, which are firm but
flexible; others are hard, tough, and rigid. You may have chewed into a very hard, tough
structure while eating meat. This was most likely a piece of connective tissue that the
butcher left behind. The important distinguishing characteristic of connective tissue is that
the matrix gives a particular connective tissue its identity.
Figure 2.4 Connective tissue components
Connective tissue is made up of many components. Many types of connective tissue are
formed from the same substance, which is made up of a mixture of salts, water, protein,
and carbohydrates. Embedded in this substance are cells and fibers. Among the cells and
fibers are elastic fibers for elasticity, collagen fibers for strength, reticular fibers for
support, microphages and white blood cells to fight infection, fat cells for storage, and
plasma cells to produce antibodies.
squamous epithelium: Epithelium consisting of one or more cell layers, the most
superficial of which is composed of flat, scale-like or plate-like cells.
cuboidal epithelium: Epithelial tissue consisting of one or more cell layers, the most
superficial of which is composed of cube-shaped or somewhat prismatic cells.
columnar epithelium: Epithelium consisting of one or more cell layers, the most
superficial of which is composed of elongated and somewhat cylindrical cells projecting
toward the surface.
glandular epithelial cells: Specialized epithelial cells that secrete bodily products such
as mucus and hormones.
Connective tissue contains one or more of three fibers—collagen, reticular, and elastic.
Their characteristics and main functions are as follows:
1. Collagen fibers are tough, strong fibers that form the major fibrous component of the
skin, tendons, cartilage, ligaments, and teeth. They are made of the amino acids glycine,
proline, lysine, hydroxyproline, and hydroxylysine. Collagen gives connective tissue its
versatility because of its ability to interconnect with other molecules and minerals and
thereby form an alloy of sorts, with a higher tensile strength than its separate parts.
Collagen fibers occur in bundles, which gives it great tensile strength.
2. Reticular fibers are delicate, supportive fibers of connective tissue that occur in
networks and support structures such as capillaries and nerve fibers.
3. Elastic fibers are extendible fibers that are designed to maintain elasticity, thus
providing resilience in tissues such as skin, arteries, and lungs.
Connective tissues that are most familiar to athletes and trainers include cartilage, bone,
tendons, and ligaments. The following section discusses them and also includes a
summary of other connective tissues.
Cartilage forms the foundation of bone tissue. It is found at bone ends, in spinal discs, and
makes up the soft bony tissue in the nose. Mature cartilage does not contain blood vessels
or nerves. It obtains nutrition through small holes that allow nutrients to seep in. Three
types of cartilage exist that are classified by their consistency: elastic, fibrous, and hyaline.
The hardness of cartilage depends on the number of collagen fibers: elastic cartilage found
in ear and eustachian tubes; tough fibrous cartilage found between bones of the spine
(disks); and hard hyaline cartilage found in bone ends, nose, larynx, and trachea.
Bones form the skeleton, which functions as support and protection for the body. Bone
both resembles and differs from cartilage. Bone is similar to cartilage in that it consists
more of intercellular substances (matrix) than cells. However, in bone, the intercellular
substance is calcified and hardened as opposed to cartilage, which is a firm gel. Calcium
salts impregnate and cement the matrix, a fact that explains the rigidity of bones.
Embedded in the calcified matrix are many collagen fibers.
Bones are not as lifeless as they seem. Within this hard, nonliving, calcified, intercellular
matrix exist many living cells. These cells continually receive food and oxygen and excrete
their wastes through the numerous blood vessels that are present in bone tissue and bone
marrow.
Tendons and ligaments are flexible, yet strong. In fact, they are the strongest
connective tissues in the body. Their intercellular matrix consists of a collagen and
reticular fiber network, which originates from the cells they surround. Tendons function to
connect muscle to bone or other structures. Tendons can be thick, like the Achilles tendon;
or they can be thin, like the aponeurosis—a thin layer of connective tissue that covers the
skull. Tendons vary based on their location in the body and the demands placed upon
them. Ligaments join bone to bone. Ligaments are most commonly found where two bones
articulate to form a joint, such as the elbow.
tendon: Connective tissue that attaches muscle to bone.
ligament: Connective tissue that connects bone to bone or bone to cartilage.
Figure 2.5 Tendons and ligaments
The functional nature of connective tissue suggests that damage to these structures is a
serious occurrence. Connective tissues consist of only a few cells and mostly nonliving
matrix, so they have a very limited capacity to regenerate themselves. This is one reason
why tendon and ligament injuries often need surgery for repair. Proper nutrition and
strength training can help build strong connective tissues that will become more resistant
to injury.
Some other types of connective tissues are: reticular tissue of the spleen, lymph nodes, and
bone marrow, which functions as a filtering medium for blood and lymph; areolar tissue,
which occurs between organs and other tissues and functions to connect; and adipose
tissue, which contains fat and is found under the skin in various spots throughout the
body. Adipose tissue functions to protect, insulate, support, and serve as a food reserve.
Other types of connective tissue include blood, myeloid (red bone marrow), and lymph.
Muscle Tissue
Muscle tissue comprises approximately 43 percent of an average man’s bodyweight and 34
percent of an average woman’s bodyweight. Over 600 muscles work together with the
support of the skeletal system to create motion. An additional 30 or so muscles are
required to insure the passage of food through the digestive system, to circulate blood, and
to operate specific internal organs. In exercise physiology, muscles are the main operative
tissue, expending energy, generating wastes, and requiring substantial nutrition. Unit 3
explains muscle tissue in more detail.
Figure 2.6 Muscle tissue
Nervous Tissue
Nervous tissue is made up of several types of cells that are responsible for the control of
the bodily functions. Nervous tissue is found in the brain, spinal cord, and nerves, which
branch out to all parts of the body. The three types of nervous tissues are neurons,
neuroglia, and neurosecretory cells. Their functions are as follows:
nervous tissue: The main component of the nervous system; the brain and spinal cord
of the central nervous system (CNS), and the branching peripheral nerves of the peripheral
nervous system (PNS), which regulates and controls bodily functions and activity.
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Neurons conduct nerve impulses, register sensory impulses, and conduct motor
impulses. The central neuron body contains a nucleus surrounded by cytoplasm, and two
projections at either end. The two types of projections are axons—which generally conduct
impulses away from the body of the nerve cell—and dendrites, which conduct impulses
from adjacent cells inward toward the cell body.
Neuroglia consist of a delicate network of branched cells and fibers that supports the
tissue of the central nervous system.
Neurosecretory cells are large neurons that produce secretions, which travel along
neuron axons and are typically released into the bloodstream. They function to translate
neural signals into chemical stimuli in the body.
Figure 2.7 Nervous tissue, found in the brain, spinal cord, and nerves
Figure 2.8 Human body systems
SYSTEMS OF THE BODY
The human body is an incredible biological phenomenon composed of several
interdependent systems that are responsible for maintaining life. Groups of body tissues
interact to form functional body units called systems. Essentially, the body is one living
system made up of many subsystems. However, for academic purposes, anatomists and
physiologists refer to these subsystems as systems. The body has 10 principal systems, and
they are summarized as follows: (1) Theintegumentary system consists of the skin and
the structures derived from it. (2) The skeletal system helps to support and protect the
body and consists of bones and cartilage. (3) The muscular system consists of large
skeletal muscles for movement, cardiac muscle in the heart, and smooth muscle of the
internal organs. (4) The nervous system consists of the brain, spinal cord, sense organs,
and nerves, which regulate other systems of the body. (5) The endocrine
system consists of the glands and tissues that release hormones and works with the
nervous system in regulating metabolic activities. (6) The circulatory system serves as
the transportation system of the body and consists of two subsystems: the cardiovascular
system and the lymphatic system. (6a) The cardiovascular system consists of the heart and
blood vessels and serves as the transportation system. (6b) The lymphatic
system protects the body against disease. (7) The respiratory system consists of the
lungs and air passageways, which supply oxygen to the body and remove carbon dioxide.
(8) Thedigestive system consists of the digestive tract and glands that secrete digestive
juices into the digestive tract and is responsible for the breakdown of foods and waste
elimination. (9) The urinary system is the main excretory system of the body, which
consists of the kidneys, ureter, urinary bladder, and urethra. (10) The reproductive
system consists of male or female gonads and associated structures, which maintain
sexual characteristics and are responsible for reproduction.
integumentary system: System of the body consisting of the skin and its associated
structures, such as the hair, nails, sweat glands, and sebaceous glands.
skeletal system: System of the body consisting of bone and cartilage that supports and
protects the body.
muscular system: System of the body consisting of large skeletal muscles that allow us
to move, cardiac muscle in the heart, and smooth muscle of the internal organs.
nervous system: System comprised of brain, spinal cord, sense organs and nerves.
Regulates other systems.
endocrine system: System consisting of the glands and tissues that release hormones. It
works with the nervous system in regulating metabolic activities.
circulatory system: System consisting of the heart and blood vessels that serves as the
transportation system.
lymphatic system: Subsystem of the circulatory system, which protects the body against
disease.
respiratory system: System consisting of the lungs and air passageways, which supplies
oxygen to the body and removes carbon dioxide.
digestive system: System of the body consisting of the digestive tract and glands that
secrete digestive juices into the digestive tract. Responsible for breaking down foods and
eliminating waste.
urinary system: Main excretory system of the body, which consists of the kidneys,
ureter, urinary bladder, and urethra.
reproductive system: System consisting of gonads, associated ducts, and external
genitals concerned with sexual reproduction.
Although each system can be separated out from the rest, without the other systems, its
function cannot be carried out to completion. For example, if the muscular system were
disconnected from the nervous system, nerve impulses sent down neurons would have no
effect on stimulating muscle contraction. Of these 10 principal systems, 6 are most
pertinent to health, physical fitness, and personal training: the respiratory system, the
circulatory system, the nervous system, the endocrine system, the skeletal system, and the
muscular system. This unit covers the first 5, and Unit 3 covers the muscular system
separately.
Respiratory System
The respiratory system consists of the lungs and air passageways leading to and from
them: mouth, throat, trachea, and bronchi. The respiratory system supplies oxygen and
eliminates carbon dioxide to tissues in helping to regulate the acid–alkaline (pH) balance
of the body. Respiration is the overall exchange of gases between the atmosphere, the
blood, and the cells.
It all begins with the lungs. This is where the air you breathe is processed; the oxygen is
removed and then transferred to the bloodstream for distribution throughout your body.
The amount of air that your lungs can process is the first limiting factor on your physical
condition.
To understand how conditioned lungs can process more air, you need to understand how
breathing works. Think of the lungs as a dairy in which bulk milk comes in and the cream
is separated from it. The cream is then bottled and sent off for distribution. Empty bottles
come back, get flushed out, and receive more cream—and the cycle begins again.
Figure 2.9 Pulmonary anatomy
Think of oxygen as the “cream” of the air you breathe. When bulk air comes into your
lungs, the oxygen is extracted from it, “bottled” in red blood cells (hemoglobin), and
then sent off on the bloodstream assembly line for distribution. When they reach the
tissue, the “bottles” exchange oxygen for carbon dioxide and water and then carry these
wastes back to the lungs, where they are flushed out. The “bottles” are then ready to pick
up more oxygen and begin the cycle again.
The air you breathe is approximately 21% oxygen and 79% nitrogen, with negligible traces
of other gasses. This ratio rarely varies. What does vary is the amount of air you can
process. If your lungs cannot process enough air, they cannot extract enough oxygen to
produce enough energy. Two factors limit the lungs’ ability to process air.
First, the lungs have very little muscle of their own. Expansion and contraction of the
lungs depends on the muscles of the rib cage and the diaphragm. As you inhale, the
muscles surrounding the lungs create a larger area in the lung cavity, thereby creating a
partial vacuum. Aided by this differential in atmospheric pressure, air then rushes in.
When exhaling, the muscles, aided somewhat by the natural elasticity of the lungs and
chest wall, contract to create greater atmospheric pressure inside the lungs than outside
your body. Inhaling is the air is being “sucked” in; exhaling is the air being “pushed” out.
The process described occurs with the body at rest. Most bodies at rest consume basically
the same amount of oxygen, and consequently they inhale and exhale just about the same
amounts of air.
Now, as you move into physical activity, the amount of air you can inhale and exhale is
limited. The first limiting factor is the size of the vacuum your muscles can create for the
lungs to expand into; the second is the size of the area they can be squeezed back into.
Conditioned athletes have the capability to inhale more air and sustain the process for
longer periods. Conditioned athletes are also more capable of exhaling more waste because
the muscles surrounding their lungs have been trained and thus are more efficient.
The second limiting factor on how much air the lungs can process is the condition inside
the lungs. Lungs vary in size; a larger person naturally has proportionately larger lungs
than a smaller person. In terms of sports performance, the concern is less about the size
(total capacity) of the lungs than with how much of that capacity is usable. This usable
portion is called the vital capacity, and it is measured in the laboratory by assessing the
amount of air that can be completely exhaled in one deep breath.
Research has shown that a conditioned person has a vital capacity equaling approximately
75% of his or her
Figure 2.10 Respiration. When the diaphragm and breathing muscles lift the rib cage,
the size of the chest cavity increases; as the rib cage lowers, the size of the chest cavity
decreases. Fluctuation in cavity volume causes air to move in and out of the lungs.
hemoglobin: An oxygen-transporting protein found in blood cells.
vital capacity: The usable portion of the lungs.
total lung capacity. However, a deconditioned person may match this percentage by virtue
of genetics. To differentiate between the two individuals, you must look at the maximum
minute volume, the amount of air that a person can process during 1 minute of vigorous
exercise. The results of this test generally provide a clear indication of who is the
conditioned individual and who is the deconditioned individual. Conditioned athletes may
force as much as 20 times their vital capacity through their lungs in 1 minute, whereas
deconditioned individuals might be hard-pressed to force even 10 times through. They
simply lack the muscle strength and endurance to perform at any higher level.
maximum minute volume: The amount of air that a person can process during one
minute of vigorous exercise.
After usable lung volume has been measured, the remainder of the air in the lungs is called
the residual volume. This volume is fixed, and even a conditioned athlete cannot
breathe it in or out. However, too much residual volume is unhealthy. If your body
deteriorates from inactivity or disease, the unusable portion of the lungs may increase,
providing less space for normal breathing, let alone vigorous exercise. Ultimately,
shortness of breath results from even light activity, such as climbing a flight of stairs.
When you need more oxygen in a hurry, the muscles controlling the lungs will not be in
condition to force high volumes of air through them, and the usable space within the lungs
may be seriously reduced.
residual volume: The remainder of the air in the lungs after the usable lung volume has
been measured.
In some before-and-after tests with Lackland Air Force Base airmen, it was
found that with just 6 weeks of conditioning, the airmen increased maximum
minute volume from 10 times to as much as 20 times their vital capacity. The
figures are both an indictment and an argument. The airmen were teenagers,
yet they could ventilate only 10 times their usable lung volume in one minute.
It makes one wonder what they had been doing all their lives to get so
deconditioned at such a young age. Then, after just a month and a half of
conditioning, they bounced back to peak ability.
The training effect can reverse both trends. Exercising the muscles surrounding your lungs
increases their strength and efficiency and helps open more usable lung space. It has the
net effect of increasing your vital capacity and reducing the residual volume. In each
instance, it makes your lungs more efficient organs to process more air and extract more of
the essential oxygen. The oxygen supply to the blood at rest is only about 1 cup per minute.
Extreme exercise in a trained athlete can step this number up to 1 gallon per minute. At
rest, only about 12 percent of the stagnant air in the lungs is renewed during each breath.
A good way to test the breathing condition of your lungs is to take a deep breath and see
how long you can hold it. Most adults in moderately good physical condition and with
healthy lungs should be able to hold their breath for 50 seconds or longer. Most
individuals in average condition have a respiration rate of 10 to 16 breaths per minute.
Respiration rate is measured at rest with the subject breathing within a normal resting
heart rate. The training effect can have beneficial effects on normal breathing, resulting in
fewer breaths per minute. Exercising the muscles surrounding the lungs increases their
strength and efficiency, which increases usable lung capacity. It has the net effect of
increasing the vital capacity and reducing residual volume. The training effect thus
transforms the lungs into more efficient organs that are capable of processing more air
and extracting more essential oxygen.
Circulatory System
The circulatory system serves as the body’s transportation system. The heart, arteries,
veins and blood vessels are parts of this system. The circulatory system consists of two
subsystems: the cardiovascular system and the lymphatic system. In the cardiovascular
system, the heart pumps blood through a vast network of blood vessels. The lymphatic
system helps preserve fluid balance within the body and protects against disease.
Figure 2.11 Chambers of the heart. Blood enters the right atrium and is pumped to the
longs via the right ventricles. It re-enters the heart at the left atrium and is pumped into
the general circulation from the left ventricle.
Figure 2.12 Systemic circuit
Anatomy of Blood
Blood has four main constituents: plasma, erythrocytes, leukocytes, and platelets.
Plasma, the fluid portion of blood, is composed of numerous chemicals including sugars,
minerals, and proteins (albumin, globulin, and fibrinogen). Erythrocytes, containing
hemoglobin, carry oxygen, supplying it to all the tissues of the body. Leukocytes, of which
several types exist, serve principally to combat infections. Platelets are important in the
mechanism of blood clotting.
plasma: The fluid portion of blood.
erythrocyte: Blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a
biconcave disc that has no nucleus. Also known as red blood cell.
leukocyte: Cell whose primary function is to combat infections; also known as white
blood cell.
platelet: Cytoplasmic body found in the blood plasma that functions to promote blood
clotting.
The total volume of blood in the body is dependent on the size of the individual and the
state of training. The average blood volume range is from 5 to 6 liters in men and 4 to 5
liters in women. The composition of whole blood is 55 percent plasma (of which 90% is
water, 7% plasma proteins, and 3% other), and 45 percent formed elements (of which
more than 99% is red blood cells and less than 1% white blood cells and platelets). Mature
red blood cells (erythrocytes) have no nucleus and therefore cannot reproduce. They must
be replaced with new cells every 4 months. This balance is very important because
adequate oxygen delivery to body tissues depends on having a sufficient number of
carriers: red blood cells. A decrease in the number or function of red blood cells can hinder
oxygen delivery and thus affect performance.
Figure 2.13 Composition of whole blood.
How Respiratory and Circulatory Interaction Works
From the lungs, the oxygen goes directly into the bloodstream—the “assembly line” of the
body. The lungs contain millions of tiny air sacs, called alveoli, around which the blood
flows. These sacs are like tiny balloons filled with air dangling in the liquid of the
bloodstream. The air is forced into these sacs by atmospheric pressure. Then, following
the law of gaseous diffusion, the oxygen moves from the area of higher pressure in the
alveoli to the red blood cells, where the pressure is lower. Going back to the dairy farm
analogy, the red blood cells are now in effect “empty bottles,” having delivered their supply
of oxygen and disposed of the returning wastes.
alveoli: Capillary-rich air sacs in the lungs where the exchange of oxygen and carbon
dioxide takes place.
Limiting factors include the number of red blood cells, the amount of hemoglobin they
carry, and total blood volume. Even if your lungs could process more oxygen, your body
tissue still would not receive more oxygen unless there were more “bottles” to put it in for
delivery.
This is another benefit of the training effect. It produces more blood, resulting in: more
hemoglobin, which carries the oxygen; more red blood cells, which carry the hemoglobin;
more blood plasma, which carries the red blood cells and, consequently, more total blood
volume. Laboratory tests have repeatedly shown that people in good physical condition
invariably have a larger blood supply than deconditioned people of comparable size. An
average-sized person may increase his or her blood volume by nearly a quart in response
to aerobic conditioning, and the red blood cell count increases proportionately.
Figure 2.14 Alveoli
So, now there are not only more “bottles” to deliver the oxygen, but more “empties” to
carry away the wastes. The removal of carbon dioxide and other waste products is just as
important in reducing fatigue and increasing endurance as is the production of
energy. It is like your home. Even if you stock your pantry with good food, you still have to
clean out the garbage regularly to maintain a livable space.
law of gaseous diffusion: Law stating that a gas will move across a semipermeable
membrane (e.g., alveolar, capillary) from an area of higher concentration to an area of
lower concentration.
The process by which the “bottles” get to the tissue level, unload the oxygen, and pick up
the wastes from the tissue cells is called osmosis. The oxygen and food particles, now in
liquid form, pass through the cell membrane, and waste products exit the cell in the
opposite direction. That basic life cycle is represented here: Materials for nourishment and
energy go in, and leftover wastes go out. To complete the cycle, when the carbon dioxide
and other wastes are carried away in the bloodstream through the veins and they reach the
lungs, the law of gaseous diffusion now works in reverse. The pressure of the carbon
dioxide in the veins is greater than it is in the alveoli, so it passes freely into the alveoli and
is exhaled with the expired air.
osmosis: The scientific process of transferring fluid between molecules.
The efficiency of this cycle, and its capacity for gas exchange, is a function of the training
effect. The more exercise the body does, the stronger the training effect will be; the less
exercise the body does, the weaker it will be.
In a treadmill test, conditioned adult males would start with a diastolic
pressure of 70 and experience only a slight increase during their run. Then,
upon stopping, they would return to normal within a few minutes. However,
deconditioned people—and especially the overweight types—might start with
a diastolic pressure of 90, then shoot up to 105 during exercise, and take 10
minutes or more to recover.
diastolic pressure: Pressure exerted on the walls of the blood vessels during the
refilling of the heart.
All of these processes are occurring with the body at rest and the heart beating at a normal
rate. Physical activity and emotional stress raise the heart rate. They also raise the blood
pressure because the heart is pumping more blood into the system at a faster rate.
Excessive demands on the heart can cause trouble in people with pre-existing medical
conditions.
Years ago, treatment for high blood pressure was rest and relaxation. However, recent
reports, such as the Surgeon General’s Report (1996) suggest that regular exercise can be
an effective means of reducing high blood pressure. Most people, especially those with
clinical conditions, reduce their blood pressure significantly after adhering to an exercise
program for even a few weeks. The blood vessels make compensatory adjustments to
handle the increased workload because of the exercise they get regularly. Almost all of the
body systems do so in response to increased stress; this adaptive response is the training
effect.
One of the most famous and amusing tests done in the area of vascularization
was reported by a researcher who set a weight on the floor, tied a rope to it,
ran the rope over a pulley fastened to the edge of a table, then sat on the other
side of the table and looped the rope over the middle finger of his right hand.
Then, in time to a metronome, he began lifting the weight. The first time, and
for many weeks thereafter, the best he could do was 25 lifts before his finger
became fatigued. To expand the experiment, he had a mechanic in the
building lift the weight occasionally, and the mechanic always beat him.
One day, about 2 months later, the researcher began his usual lifts, but found
his finger wasn’t tired at 25. He kept going and ultimately reached 100. He
suspected what had happened and brought the experiment to a rather
unorthodox conclusion. He invited the mechanic in again and made a small
bet that he could beat him. The mechanic accepted and lost.
What the researcher suspected, of course, was that his finger muscles had
undergone vascularization in response to the adaptive stress of exercise.
More blood vessels had opened up, creating new routes for delivering more
oxygen. And they apparently did not open up one at a time, but a whole
network at a time.
Another effect of conditioning on the blood vessels is an augmented blood supply made
possible by the creation of new routes (called vascularization) supplying blood to the
working muscles. This vascularization is the most essential factor in building endurance
and reducing fatigue in the skeletal muscle. Saturating the tissue with oxygen and carrying
away more waste is a crucial factor in the health of the heart, the most important muscle of
all. Larger blood vessels supplying the heart tissue with energy-producing oxygen
considerably reduce the chances of cardiac failure. Even if a heart attack were to occur, the
improved blood supply would help to keep surrounding tissue healthy and improve
chances for a speedy recovery.
One final problem involving the blood vessels is fat metabolism. As discussed in Unit 1,
“metabolism” is a big word with a reasonably simple meaning: It means change. You have
already been introduced to one type of metabolism: energy metabolism, where foodstuffs
are burned by oxygen and converted into energy. Another form of metabolism is tissue
metabolism, in which foodstuffs are changed to make new tissue.
fat/lipid metabolism: A metabolic process that breaks down ingested fats into fatty
acids and glycerol and then into simpler compounds that can be used by cells of the body
for general bodily function as well as energy production.
Fat is one of the foodstuffs; proteins and carbohydrates are others. Dietary fat is important
because it is one of the major factors in the development of arteriosclerosis. It is also
important in the development of cholesterol. The crust found on the inner walls of arteries
in arteriosclerosis (hardening of the arteries) contains large amounts of cholesterol.
The body can tolerate and easily metabolize a moderate amount of fat. But as you will
learn later in this text, high-fat diets strain its metabolic capabilities. When this happens,
fat circulates in the bloodstream for prolonged periods following fatty meals, and how long
it takes to get rid of it depends on the body’s condition.
The training effect does three things for blood vessels:
1. It enlarges them and makes them more pliable to pressure.
2. It increases their number for saturation coverage.
3. It helps keep their linings clear of corrosive materials.
Tissues are the end of the assembly line, where the oxygen is turned over to the consumer
and the waste products are picked up for carting away. Each cell is like a small factory; it
has its own receiving and shipping facilities, storeroom, and power plant for creating
energy, heat, and new protoplasm—the stuff of which all cells and all living things are
made. All the food you eat and all the oxygen you breathe is meant to serve this one tiny
little factory.
In a study on fat metabolism, a group of volunteers—well-conditioned men,
average men and men in poor condition—fasted overnight to eliminate
interference from other foods. On the morning of the test, each drank 1 1/2
pints (3/4 qt) of heavy cream and nothing else. Then, still without eating,
blood counts were taken every few hours to see how fast the fat was processed
out of the bloodstream. The conditioned subjects lowered their total fat to
normal within four hours. Some of the deconditioned bodies took up to ten
hours—more than twice as long!
The fat intake from this study was all from one sitting. Consider all the fat
your body takes in during the day and you can understand the body’s job of
getting rid of fat. Some bodies can’t do it, and problems become inevitable.
Ideally, healthy fat metabolism depends on a combination of a low-fat diet
and aerobic exercise. But studies have shown that a high-fat diet and aerobics
are preferable to a low-fat diet and no exercise.
When donating blood, as thousands of individuals did in a patriotic response
to the September 11th attack on the United States, the removal of one unit
(nearly 500 ml) represents approximately an 8 to 10 percent reduction in
both total blood volume and in the number of circulating red blood cells.
Since blood is 55 percent plasma, of which 90 percent is water, donors are
advised to drink plenty of fluids to help replace plasma volume to normal
within 24 to 48 hours. However, since red blood cells are formed elements, it
takes at least six weeks to reconstitute the red blood cells. Resistance training
is not detrimentally affected by blood donation because it predominantly
relies on the ATP/PCr or glycolytic systems to produce ATP, both of which are
anaerobic systems. However, blood loss greatly compromises the
performance of endurance athletes by reducing the number of available red
blood cells and thus reducing the oxygen-delivery capacity.
Blood serves many useful purposes in the regulation of normal body
functions. From transportation to temperature regulation and acid-base
balance, the importance of blood cannot be overstated and we at ISSA
encourage all our students to consider their role in helping others through
blood donation.
Heart
The heart is the magnificent engine that keeps the whole assembly line going. It takes
oxygen-laden blood from the lungs and pumps it throughout the body, and it takes carbon
dioxide–laden blood back from the body and pumps it into the lungs where it is exchanged
for more oxygen.
The heart begins working before birth and continues to work until death. Ironically, the
heart works faster and less efficiently when you give it little to do than it does when you
make more demands on it. It is a remarkable engine.
Both anaerobically and aerobically conditioned people who exercise regularly tend to
have a resting heart rate of about 60 beats per minute (bpm) or less. A deconditioned
person who does not exercise may have a resting rate of about 80 bpm or more. Women
tend to have a slightly higher heart rate than men, as do children. Even though you may
appear to be in great condition, obesity, stress, and many other factors can speed heart
your rate considerably.
anaerobic: Occurring without the use of oxygen.
aerobic: Occurring with the use of oxygen, or requiring oxygen.
resting heart rate: The number of times the heart beats in one minute: 72 beats per
minute for the average adult.
Suppose that the two people in the previous example were at complete rest for a full 24
hours. A comparison between their two resting heart rates would look like this:


Conditioned person
60 bpm, times 60 min =3,600 beats per hour (bph)
3,600 bph × 24 h =86,400 beats per day (bpd)
Deconditioned person
80 bpm × 60 min = 4,800 bph
4,800 bph × 24 h =115,200 bpd
Even at complete rest, a deconditioned person who does not exercise the heart forces it to
beat nearly 30,000 times more during every day of life. But no one is at complete rest 24
hours a day, and for ordinary activity such as getting up from a chair, walking across the
room, and climbing a flight of stairs, the deconditioned heart would beat proportionately
faster than a conditioned heart for the same activity.
What have you done for your heart lately? In considering how healthy your heart is, you
must look at two factors: the tissue itself and the number of times it beats during rest or
exercise.
Figure 2.15a Interior view of the heart
Figure 2.15b Vascularization of the heart
Vascularization—the development of new capillaries and the enlargement of
the existing blood vessels—was best demonstrated by an amazing athlete
named Clarence DeMar. During his lifetime, he participated in more than
1,000 long-distance races. He entered the 26 mile Boston Marathon 34 times,
winning it seven times and finishing in the top 10 on 15 other occasions.
“Mr. Marathon” was a man who enjoyed running. He worked nights as a
proofreader for a New England newspaper, operated a small farm and still
found time to teach classes at a reformatory for boys, in addition to keeping
in condition for his cross-country races.
Clarence ran his last race, a simple 10-mile affair, when he was 69. He died of
cancer a year later, working up to two weeks before his death. His family
allowed an autopsy. His heart was a museum piece, but the most striking
discovery was the condition of the coronary arteries, the arteries that supply
the heart muscle. They were two to three times their normal size! Some of our
sedentary types not only do not have enlarged arteries, but the small ones
they do have are clogged with debris which reduces the openings even more.
Heart Tissue
Heart tissue is mostly muscle. Unlike the lungs, the heart does its own work, which is
unquestionably the most important work in the body. The health of heart tissue is
determined by its size and how well it is supplied with blood vessels.
Hearts come in three sizes. A normal, deconditioned heart is relatively small and weak
because, like any muscle that is not exercised properly, it begins to atrophy (waste away).
An enlarged unhealthy heart normally grows to compensate for a deficiency in the
cardiovascular system, hypertension, or other vascular deformity. Such enlarged hearts
are not as efficient as hearts that grow large through training. Despite their exterior size,
their interior volume is not as large, so they cannot pump as much blood with each stroke.
The conditioned heart is strong and healthy. It is relatively large and highly efficient; each
stroke pumps more blood with less effort. It is beautifully resilient and, like any great
athlete, it does its job effectively and efficiently.
Vascularization plays a prime role in the heart, because more vessels allow for better
function. For its own energy, the heart needs the same oxygen it is pumping around the
body for the other muscles. A healthy heart is characterized by a conspicuously favorable
blood supply. Heart tissue is saturated with oxygen by healthy blood vessels. It is like a
lawn with built-in watering jets versus one watered with a small garden hose. The hose
might water the entire lawn eventually, but during a hot spell, it might take too long and
some of the lawn might burn up. If part of your heart could not get enough sprinkling, it
could also “burn up,” leading to a heart attack.
A healthy heart depends on the health of the cardiac tissue, and healthy cardiac tissue
depends on saturation by way of large healthy blood supply routes. This saturation
coverage (vascularization) is one of the most important benefits of the training effect.
Nowhere is the training effect more evident or more important than in the heart.
Heart Rate
The second factor that indicates the health of the heart is the heart rate. As they grow
larger and stronger, conditioned hearts can beat more slowly because they are pumping
more blood with each stroke. Nearly all of the great distance runners have had low heart
rates. In fact, some are reported to have a resting rate of as little as 32 bpm. Even highly
conditioned anaerobic athletes—such as football players, sprinters, and weightlifters —
have resting heart rates far below the average person. The average young office worker has
a resting heart rate of about 75 to 80 bpm. To determine resting heart rate, have your
client sit still for 5 minutes, then take his or her pulse and count the beats for a full 60
seconds. If the heart rate is at 80 bpm or above, then your client is not likely in good
condition.
Treadmill tests show that those with conditioned hearts can literally do twice
as much work, run twice as fast or twice as long, and with a lower heart rate
than those with deconditioned hearts. Some supremely conditioned athletes,
like distance-runner Peter Snell, have been run to exhaustion on treadmills,
yet their heart rates never exceeded 165 to 170 beats per minute.
The good news is you can help a client change that condition with training. Dr. J.S.
Skinner, formerly with the U.S. Public Health Service, enlisted a group of desk-bound
executives, 35 to 55 years of age, in an exercise program. After a training program of 6
months, their resting heart rates dropped an average of 10 bpm. (Skinner, 1993)
Training also reduces maximum heart rate (HR max), which is just as important.
Healthy hearts will peak, without strain, at 190 bpm or less, while poorly conditioned
hearts may go as high as 220 bpm or more during exhausting activity, which is
dangerously high depending on the age of the subject. You can estimate maximum heart
rate (HR max) by subtracting your age from 220. For example, for a 35-year-old
individual, it would be 185 because 220 − 35 = 185.
maximum heart rate (HR max): The highest rate at which an individual is capable:
220 minus age in years is equivalent to maximum heart rate.
Eq. 2.1
What lower heart rates really mean is that when at rest, the heart is conserving energy
(saving at least 15,000 beats per day) And that during activity, it has built-in protection
against beating too fast and suffering strain or failure.
Finally, training can condition the heart to not only reduce its maximum rate, but also
strengthen it so that it can hold near-maximum rates for longer periods before fatigue sets
in. Some of the Gemini astronauts had heart rates of around 170 during their exhausting
extravehicular activity. In addition, Norwegian cross-country skiers have been known to
hold heart rates of up to 170 for as long as 2 1/2 hours at a clip.
Another type of heart rate has nothing to do with physical exercise. It is called the
anticipatory rate or tension rate. You might want to think of it as the emotional heart rate.
For example, the telephone rings unexpectedly in the middle of the night, and you can
almost hear your heart pound as you rush to answer it. You are due for a promotion that
does not come, and you get worked up just thinking about it. These and other little crises
of daily life affect the heart. But training can reduce this effect.
This response to mental and physical stimuli makes the heart a unique muscle. Two
systems in your body prepare you for the fight-or-flight response, which starts the heart
pumping and rushes more oxygen around before you even make a move. In periods of
acute emotional stress, the sympathetic nervous system, an automatic system that
speeds up most activities in the body, combines with the output of the adrenal glands to
produce a high level of hormones in the blood. When these hormones reach the heart, they
cause it to increase in rate and strength of contraction.
sympathetic nervous system: An automatic system that speeds up most activities in
the body.
adrenal glands: Two glands that release hormones which helps the body cope with
stress.
However, with deconditioned hearts, the slowing down sometimes does not happen and
the heart takes off, beating at an excessively fast rate, possibly leading to a heart attack.
With conditioned hearts, there is a better balance, and you can go at an all-out effort but
still control it before you go too far. A high, potentially damaging level of hormones is
simply never reached. This, too, is part of the training effect. These hormones have less of
an effect on a conditioned body, possibly due to more efficient utilization or to decreased
production. Add to this the fact that a conditioned person’s heart is already trained to level
off at a relatively low maximum rate, and he or she has a built-in protection against
uncontrollable emotional crises. A deconditioned person does not have this protection. If
the deconditioned person is also someone who gets overly excited even in minor
emergencies (a hyper reactor), then he or she has two strikes: too much emotion and too
little built-in physical protection.
Stroke Volume
Stroke volume is the term used to describe how much blood is pushed out of the left
ventricle with each beat. One very important element in the overall training effect is the
stroke volume of the heart. The more the heart pumps out with each beat, the less
frequently it is required to beat.
stroke volume: The volume of blood pumped out of the heart into the circulatory system
by the left ventricle in one contraction.
Another important term to remember is left ventricle ejection fraction. Say, for
example, you pump a pint of blood out of the left ventricle with each beat. Is that 50
percent of what is there? Is it 70 percent? 90 percent? A well-trained athlete can push out
about 95 percent of the blood in the left ventricle while working at 80% of his or her
capacity. That is great! The average (sedentary) person only pushes out about 75 percent
while working at 80 percent maximum. Increased stroke volume means that the more
blood that is pumped out with each beat, the lower the heart rate is.
left ventricle ejection fraction: The percentage of blood inside the left ventricle
pushed out into the body after contraction.
Once the blood is pumped out of the heart, it goes to the working muscles. How efficiently
the oxygen it’s carrying there is taken into the muscle cells and utilized is called maximal
oxygen uptake, or O2 max. The training effect benefits the heart in several ways. It
develops a strong, healthy muscle that works with less effort during moments of relaxation
or moments of peak physical exertion. By doing so, the heart maintains large reserves of
power to handle whatever physical or emotional stress is imposed upon it.
maximal oxygen uptake ( O2 max): The maximum usable portion of oxygen uptake
over a period of time.
Digestive System
The digestive system starts at the mouth, runs some 25 feet through the trunk of the
body, and ends at the anus. It is basically a strong muscular tube lined with thick
epithelium with specialized cells, which differ depending on which part of the digestive
system you examine. The digestive system is also referred to as the alimentary canal,
gastrointestinal system, and the gut. The digestive system is the life support of the body
and the connection with the external environment. The body consumes food and then
breaks it down into useful biomolecules in order to obtain the energy necessary for life, as
well as create the building blocks necessary for growth.
digestive system: System of the body consisting of the digestive tract and glands that
secrete digestive juices into the digestive tract. Responsible for breaking down foods and
eliminating waste.
Digestion is a process by which food is broken down through chemical and physical
means so that nutrients can be absorbed. Nutrients are absorbed through the intestinal
walls, transported by the blood to the liver, and then transported further onto the trillions
of cells through the bloodstream. As you will soon discover, the digestive system is quite
complex and remarkable.
digestion: The process of mechanical or chemical breakdown of food into absorbable
molecules.
Functions of the digestive system include the following:







Receipt, mastication (chewing), and transport of ingested substances and waste products
Secretion of acid, mucus, digestive enzymes, bile and other materials needed to break
down food
Digestion of ingested foodstuffs
Absorption of nutrients
Storage of waste products
Excretion
Auxiliary functions


Figure 2.16 Digestive track

Physical Components



The digestive system is made up of several anatomically different structures that
make up the gut and several organs attached to the gut that provide essential
functions to the entire process of digestion. For example, the pancreas supplies
important enzymes to help break apart complex food substances. This section
reviews these major structures and discusses their functions.
Mouth
Food enters the digestive system through the mouth. The mouth has four functions
that it exerts on the ingested food. First, the mouth physically breaks apart food by
mastication (more commonly referred to as chewing), thus reducing it in size.
Chewing your food thoroughly is vital to digestion. Thorough mastication ensures
that you physically reduce in size the foodstuffs so that the stomach can perform its
digestive functions more easily.


Figure 2.16a Mouth

Second, it mixes the food with saliva, creating a moist mass, called a bolus, which is
then made ready for swallowing. The saliva also contains the digestive enzyme
ptyalin, which begins the chemical breakdown of starch (carbohydrates). Saliva also
serves to lubricate the food for its journey down the esophagus into the stomach.
Mucus proteins in the mouth also help

the food particles stick together. The masticated food mass is swallowed and passed
through the pharynx and then into the esophagus.

Third, the mouth regulates temperature by either cooling or warming the food.
Temperature regulation is important as enzymes function at their best within a
narrow temperature range. For humans, this range is held closely to normal body
temperature. Also, delivery of cold food can hasten the emptying of the stomach and
reduce the efficiency of digestion. Although this accelerated digestive process is
generally viewed as negative, one exception is when drinking fluid before and during
exercise or competition. Emptying fluids from the stomach faster will rehydrate the
body more quickly. The fourth major function of the mouth is that it consciously
initiates swallowing when the food is ready.


Esophagus
The esophagus extends between the pharynx and stomach and is the transport
conduit for food and water traveling to the stomach. When the bolus enters the
esophagus, an involuntary wave of muscle contractions is triggered, propelling the
food mass down into the stomach. This muscle contraction action is known as
peristalsis. This peristaltic wave travels down the esophagus at the rate of about 3
inches per second. Once at the base of the esophagus, a ring-like muscle (the
esophageal sphincter) is reached, which relaxes to allow the food into the stomach.
Keep in mind that at the same time food is let into the stomach, the esophageal
sphincter is keeping food from spurting out of the stomach, back up the esophagus.
If the sphincter weakens or malfunctions, the acidic contents of the stomach may
shoot up into the esophagus and produce an unpleasant, bitter sensation in the
throat known as heartburn. Heartburn has nothing to do with the heart; the term
developed because the pain may develop in the area of the chest associated with the
heart. To reduce stress on the esophageal sphincter, it is a good practice to eat sitting
upright and avoid overfilling the stomach with huge meals.


Figure 2.16b Esophagus

Stomach

The stomach is a muscular sac about 2 quarts in volume. It is responsible for the
storage and gradual release of food into the small intestine, digestion through
chemical secretions and the physical activity of churning the digesting food, and
transport of ingested food down the gut.

The stomach secretes several types of substances to aid in the breakdown of food.
Mucus acts as a protective layer to lubricate the stomach wall and a buffer against
acidic secretions. Hydrochloric acid is also secreted in the stomach and helps to keep
the stomach relatively free of microorganisms (bacteria) while maintaining the low
pH inside the stomach. Hydrochloric acid also acts to catalyze the action of pepsins,
which begin the digestion of proteins.

Intrinsic factor is a secretion that binds with vitamin B12 and allows it to be
absorbed in the small intestine. The hormone gastrin is also secreted in the stomach
and helps regulate stomach secretions during digestion. The enzymes rennin,
pepsin, and lipase are also secreted. They function to breakdown or begin the
breakdown process of several nutrients. Rennin works on milk protein (casein) to
prepare it for pepsin action. Pepsin breaks down protein in the presence of
hydrochloric acid. Lipase is the enzyme that breaks down fat molecules.


Figure 2.16c Stomach

Macronutrients are nutrients that are needed in relatively large amounts in the
diet; they include carbohydrate, fat, and protein. When macronutrients are taken
alone, they leave the stomach at different rates of time. Carbohydrates empty from
the stomach the quickest. For this reason, pure carbohydrate drinks taken during
exercise can get into the bloodstream fast and replenish glucose—the body’s primary
energy source. Proteins empty from the stomach next in time sequence, and fats take
the longest to empty out. When carbohydrates, proteins, and fats are consumed
together, they get mixed up, causing the stomach to take longer to empty. The
stomach normally takes 1 to 4 hours to empty, depending on the amount and kinds
of foods eaten.

macronutrients: A category of nutrients: including—carbohydrates, proteins, and
fats — that are present in foods in large amounts.

While the intestines are known as the primary location for absorption, the stomach
can absorb some nutrients as well. The stomach can absorb water, glucose, alcohol,
aspirin, some other drugs, and some vitamins, such as niacin, among other things.

The fact that water and glucose can be partially absorbed through the stomach is a
benefit for quick replenishment of these nutrients during exercise. Some popular
sports drinks take advantage of this fact and contain glucose as an
ingredient. Fructose is another common ingredient; however it is absorbed more
slowly. Complex carbohydrates may also be added to sports drinks because they
release glucose at a slow rate as they are digested. Glucose ingestion can help spare
glycogen stores, but it must be ingested within a half hour of exercise or it can cause
an influx of insulin, which will upset energy generation during exercise.

fructose: Fruit sugar.

The stomach only begins the process of breaking down complex molecules.
Complete digestion of these substances occurs farther along in the digestive tract.
Complex molecules are broken down into their smaller components (e.g., proteins
into amino acids). This breakdown process, also called hydrolysis, continues in the
intestines when the partially digested material in the stomach enters the small
intestine through the pyloric sphincter muscle. At this stage, it is called chyme.

lipogenesis: The formation of fat.

Small Intestine

The small intestine stretches about 12 feet long and is divided into three main
regions: duodenum, jejunum, and ileum. The duodenum is connected to the
stomach and makes up the first part of the small intestine. Some absorption takes
place here, but it is primarily a location for the storage and continued breakdown of
food. The next regions of the small intestine, the jejunum and ileum, are responsible
for the majority of nutrient absorption.

To accomplish complete absorption, the inside surface of the small intestine has a
unique anatomy. Instead of being a flat surface, like that of the skin, the small
intestine is lined with special cells called villi. These villi are very small finger-like
projections that line the entire inner surface of the intestine. The surface area of the
intestine is greatly increased by the villi. Each villus is served by blood vessels. When
nutrients pass through the cells of the villus, they are transported into the blood
vessels and then to the liver.

Another transport system, the lymphatic system, is also present in the villus. The
lymphatic system mainly transports fat. A small projection called a lacteal also
extends into the villus and is responsible for about 60 to 70 percent of the ingested
fats being transported to the liver. Shorter fats can be taken up through the blood
vessels and transported directly to the liver from the intestines.


Figure 2.16d Small intestine
Large Intestine and Rectum
The large intestine is about 3 feet long. The area where the ileum and large intestine join is
called the cecum. The vermiform appendix is also located in this area. In the large
intestines some final absorption of water, minerals, and vitamins occurs. Bacteria are
present in the large intestine, and through their metabolism, they produce vitamins that
are absorbed, such as vitamin K. The large intestine (also called colon) stores the waste
products of digestion. The further decomposition of fecal matter by bacterial action
produces gas, and depending on the nutrient substrate that makes it down to the colon,
the amount of gas produced varies. When the proper stimulus occurs, the colon empties its
contents into the rectum, triggering defecation. Normally, the rectum remains empty and
rectal filling occurs due to peristalsis. The more fiber in the diet, the softer the feces and
the easier it is to eventually defecate.
Figure 2.16e Large intestine
Pancreas
The pancreas is situated along the small intestine near the stomach and is an accessory
organ of the gut. The pancreas produces several secretions that are important for digestion
and absorption of the nutrients that are secreted into the small intestine. The pancreas
produces another vital secretion to help control carbohydrate metabolism. These
hormonal secretions are insulin and glucagon. Insulin is secreted into the bloodstream by
the pancreas during a meal. It functions to mediate the transport of glucose and amino
acids across cell membranes. It also fosters lipogenesis, which is the formation of fat.
Insulin has an anabolic function in the body. Anabolism refers to all the chemical reactions
and changes that build new substances for growth and maintenance.
The hormone glucagon is functionally the opposite of insulin. It initiates a series of
reactions that causes the breakdown of glycogen to mobilize glucose into the blood for
energy. During exercise, glucagon levels in the blood are increased, liberating energy for
exercise. Insulin and glucagon work together in a seesaw fashion to maintain appropriate
blood glucose levels.
Figure 2.16f Pancreas
Liver and Gallbladder
Digestion is not complete until the nutrients are delivered to the liver and then released
into the bloodstream. The intestines are connected directly to the liver by the portal vein.
The nutrients taken up from the intestines are delivered directly to the liver. Fats that
travel through the lymphatic system enter the bloodstream directly and then are circulated
to the liver for processing. In general, nutrients are control-released from the liver into
general circulation.
The liver cells process the digested nutrients. Some nutrients are used immediately and
others are stored for later use. Liver cells can change nutrients into substances that the
body will need and store them until they are required. The liver acts as a processing organ
that is responsible for maintaining nutrient balance and storing some essential nutrients
and glycogen (glucose) for energy. Glucose stored in the liver is used mainly to supply the
brain with energy.
The gallbladder is a storage sac for a digestive mixture called bile. Bile is a solution of
cholesterol, bile salts, and pigments. Bile is secreted into the small intestine in the
duodenum. It is essential for the action of lipase, for the digestion and absorption of fats,
and for the absorption of fat-soluble vitamins.
Figure 2.16g Liver and gallbladder
Factors Affecting Digestion
The act of eating should not be taken for granted. Developing good eating habits enhance
the proper digestion of food. To get the most mileage out of meals, consider the following
points:







Eat slowly, and chew food thoroughly.
Maintain posture in an upright position. Avoid eating while lying down.
Eat several meals of moderate size, as opposed to eating a few large meals.
Eat while calm. Nervousness can affect the movements of the digestive system and cause
gastrointestinal disturbances.
Allow some time for digestion to occur. Strenuous physical activities should be avoided
directly after eating.
Avoid foods that may irritate the stomach, such as hot spices and alcohol.
Consult a doctor if you think you have a digestive system disorder.
Nervous System
The nervous system is the control center of the body and the network for internal
communication. A skeletal muscle cannot contract until it is stimulated by anerve
impulse. Without the central control of the nervous system, coordinated human
movements are impossible.
nervous system: System comprised of brain, spinal cord, sense organs and nerves.
Regulates other systems.
nerve impulse: A brief reversal of the membrane potential that sweeps along the
membrane of a neuron.
Figure 2.17 The nervous system The two major divisions of the nervous system are the
central and peripheral systems. The central nervous system includes the brain and the
spinal cord. The peripheral nervous system has two subdivisions: the autonomic and
somatic systems. The autonomic nervous system acts on blood vessels, glands, and
internal organs. It is divided into two parts: the parasympathetic nervous system, which
slows body functions thus conserving energy; and the sympathetic nervous system,
which speeds body functions and thus increasing energy use. The somatic nervous
system primarily innervates the skeletal muscles, so it is most involved with physical
activity.
Organization of the Nervous System
The nervous system is made up of two major parts: the central nervous system
(CNS) and the peripheral nervous system (PNS). The central nervous system is
comprised of the brain and the spinal column. You should think of the CNS as being one
organ and not separate entities. The CNS receives messages and, after interpreting them, it
sends instructions back to the body. The peripheral nervous system does two things: It
relays messages from the CNS to the body (the efferent system) and it relays messages
to the CNS (the afferent system) from the body.
central nervous system (CNS): System of the body comprised of the brain and spinal
column.
peripheral nervous system (PNS): Relays messages from the CNS to the body (the
efferent system) and relays messages to the CNS (the afferent system) from the body.
efferent system: System designed to cause action; consists of the somatic and
autonomic systems.
afferent system: The part of the PNS that sends messages to the CNS.
The system seems no more complex than turning a light switch on and off, but it does get
more complicated. For example, the efferent system—the system designed to cause
action—is divided into two distinct and important parts: the somatic system, which is
responsible for voluntary action; and the autonomic system, which processes and
activates involuntary action.
somatic system: System responsible for voluntary action.
autonomic system: System that processes and activates involuntary action.
The afferent system—the part of the PNS that sends messages to the CNS—receives
messages through these three classes of receptors:
1. Proprioceptors are located in joints, muscles, tendons, and the inner ear. They are
responsible for picking up messages such as body position and movement (kinesthesia).
2. Exteroceptors are located near the surface of the skin. They receive information from
outside the body such as sight, touch, pressure, or temperature.
3. Interoceptors, are located in blood vessels and viscera, which report inner body
sensations such as hunger, thirst, pain, pressure, fatigue, or nausea.
The functions of the nervous system as a whole are widely varied, so it is often simpler to
remember the three main things that the nervous system does for the human body.
1. It senses changes inside and outside the body.
2. It interprets those changes.
3. It responds to the interpretations by initiating action in the form of muscular contractions
or glandular secretions.
Many articles and rhetoric exist regarding the crucial link between your mind and your
body: That link is your nervous system—the central nervous system and the peripheral
nervous system. The following section explores some of the implications of this mind–
body link.
Neural Adaptations: The Mind–Body Link
Can you modify your nervous system to your advantage? That is the big question. What
good does it do for you to know all about how the nervous system works unless you can
gain some sort of tangible payback? And, if you can expect some sort of physical reward
for working hard to understand the mind–body link, will the reward be of sufficient
magnitude to warrant giving it the attention and time to extract payment?
The answer to that last question is a resounding YES! Not only can you modify certain
aspects of nervous system function, but the rewards in terms of athletic success can indeed
be significant. Some of the most apparent areas of concern to athletes are improved
strength output, better mental concentration, greater training intensity, pain
management, and glandular secretions. All of these areas are modifiable to at least a
measurable degree and can therefore improve your efforts in the gym. All are inextricably
related to and controlled by your nervous system.
Figure 2.18 Mind-body link
Strength is ultimately controlled by the mind. The strength of your muscle contraction is
modified by both internal and external stimuli, which the CNS interprets on the basis of
both built-in defense mechanisms (e.g., your muscle spindles and Golgi tendon organs) as
well as past experience. Strength output then is a voluntary movement. The stimulus for
which originates in the various receptors is interpreted by the brain, and is called into
action by efferent motor neurons leading from the CNS to the muscles.
contraction: The shortening of a muscle or increase in tension.
What part of this process can be modified to produce greater strength? It is probably true
that the excitation threshold of individual motor units inside contracting muscles can be
altered somewhat, as can that of the Golgi tendon organs. Heavy training, explosiveness
training, and full amplitude movements appear to modify these elements to a measurable
degree, thereby improving strength output.
endocrine system: System consisting of the glands and tissues that release hormones. It
works with the nervous system in regulating metabolic activities.
But the greatest source of modification lies in the mind—the brain. How you perceive the
weight, how you approach training, how you view its importance in impacting the rest of
your life, and how strongly you cherish your goals all have a degree of influence on how
much you can lift. Therefore, understanding neural adaptations can help you motivate
your clients to reach success.
PSYCHOLOGICAL EFFECT
The mind can benefit as much as the body does from exercise. Research in the
area of psychology and physical activity supports a relationship between
physical fitness, mental alertness, and emotional stability.
An example of this relationship is that improved endurance makes the body
less susceptible to fatigue and consequently less likely to commit errors,
mental or physical. Your performance, whatever your job, can be sustained
longer without the necessity for frequent breaks. People who are physically fit
usually have a better outlook, have a little more self-confidence, and often do
well in whatever their talents and ambitions prompt them to try.
Endocrine System
The endocrine system works with the nervous system to maintain the steady state of the
body. The endocrine system helps regulate growth, reproduction, use of nutrients by cells,
salt and fluid balance, and metabolic rate. The endocrine system is also important in stress
regulation. The endocrine system consists of tissues and glands that secrete chemical
messengers called hormones.
Importance of Hormones
Hormones are essential to the function of the human body. Every morsel of food you eat,
every supplement you ingest, and every training act you perform in the gym is modified in
some way by the hormonal interactions each act instigates. You are virtually captive to
your hormones.
Types and Functions of Hormones
Various glands that comprise the endocrine system secrete hormones. The two types of
hormones, steroids and polypeptides, diffuse into the blood and course through your body
and eventually act upon a target organ. According to scientists, we have only a minute idea
as to what actions each hormone has individually or how they interact.
Hormones are made up of amino acids and can be divided into several classes based on
their chemical makeup. The classifications are amino acid derivatives, peptides/protein
and steroids. It is the chemical structure that influences the way in which the hormone is
transported in the blood and the manner that it exerts its effects on the tissue (or
muscles). In general terms, the chemical structure of the hormone determines how it will
exert its effects on the
Figure 2.19 The endocrine system
given tissues. For example, while the lipid-like structures of steroid hormones require that
they be transported bound to plasma protein (to dissolve in the plasma), that same lipidlike structure allows them to diffuse through cell membranes to exert their effects. These
hormones exist in very small quantities in the blood and are measured in micrograms,
nanograms, and picograms.
Steroidal hormones are produced from cholesterol in the gonads and the cerebral cortex,
while polypeptide hormones are manufactured in the many other glands (table 2.1) from
various amino acid combinations.
Hormones regulate nearly all your bodily functions. They regulate growth and
development, help us cope with both physical and mental stress, and they regulate all
forms of training responses including protein metabolism, fat mobilization and energy
production. In a nutshell, they do it all.
It is very important to remember that endocrine function does not function independently
of the nervous system. These two systems act together as synergists in hormonal
regulatory functions. Therefore, fright, pain, cold, and all other senses of both
environmental and bodily happenings will activate hormonal responses in a complex
array.
Hormones can act in these three ways:
1. Alter the rate of synthesis of cellular protein
2. Change the rate of enzyme activity
3. Change the rate of transport of nutrients through the cell wall
Although the effects that hormones exert directly upon various bodily functions are
complicated to understand, the resultant and indirect effects, are often of greatest concern
to a bodybuilder. It is like a cue ball hitting
Table 2.2
Hormonal Response to Exercise
CATEGORY
HORMONE
TRAINING RESPONSE
HypothalamusPituitary Hormones
Growth hormone
(GH)
No effect on resting values; trained
individuals tend to have less dramatic rise
during exercise.
Thyrotropin (TSH)
No known training effect.
Corticotropin
(ACTH)
Trained individuals have increased
exercise values.
Prolactin (PRL)
Some evidence that training lowers resting
values.
FSH, LH, &
Testosterone
Trained females have depressed values.
Trained males have depressed
testosterone, with probably no change in
LH and FSH.
Posterior Pituitary
Hormones
Thyroid Hormones
Adrenal Hormones
Pancreatic
Hormones
Kidney Hormones
Vasopressin (ADH)
Some evidence that training results in
slight reductions in ADH at a given
workload.
Oxytocin
No research information available.
Thyroxine
Reduced concentration of total T3 and an
increased free thyroxine at rest.
Triiodothyronine
Increased turnover of T3 and T3 during
exercise.
Aldosterone
No significant training adaptation.
Cortisol
Trained individuals exhibit slight
elevations during exercise.
Epinephrine &
Norepinephrine
Decrease in secretion at rest and same
exercise intensity after training.
Insulin
Training increases sensitivity to insulin;
normal decrease in insulin during exercise
is greatly reduced in response to training.
Glucagon
Smaller increase in glucose levels during
exercise at both absolute and relative
workloads.
Renin, Angiotensin
No apparent training effect.
another ball, which in turn causes yet a third ball to go into the pocket. The cue ball had a
direct effect upon ball number two, but an indirect effect upon ball number three.
Hormones and Blood Sugar Regulation
The natural regulatory system in the body automatically maintains close control over the
level of blood glucose. The body has approximately 10 grams of blood-borne glucose
circulating continuously. If blood sugar levels increase, then the pancreas releases insulin.
If blood sugar levels are too low, then glucagon is released (see Figure 2.20.)
Insulin
Insulin is a hormone released from your beta cells in the islets of langerhans in the
pancreas. It increases cellular uptake of glucose, which in turn causes increased synthesis
of muscle glycogen. This leads to a decrease in blood-borne glucose, which then causes a
decrease in insulin production. During prolonged workouts, blood glucose reduction along
with decreased insulin production increases the mobilization of stored fat.
insulin: A polypeptide hormone functioning in the regulation of the metabolism of
carbohydrates and fats, especially the conversion of glucose to glycogen, which lowers the
blood glucose level.
Figure 2.20 Maintenance of blood glucose levels under normal conditions.
Glucagon
Glucagon performs the opposite function of insulin. It plays a role in getting more
glucose into the blood when needed by stimulating both glycogenolysisand
gluconeogenesis in the liver. The glucose is released into the bloodstream and once again
raises the insulin levels.
glucagon: A hormone produced by the pancreas that stimulates an increase in blood
sugar levels, thus opposing the action of insulin.
glycogenolysis: Process describing the cleavage of glucose from the glycogen molecule.
The process of gluconeogenesis (the production of glycogen from noncarbohydrate
sources) activates yet another process. The liver absorbs blood-borne amino acids. This
absorption can adversely affect ability to grow because of the reduced availability of the
amino acids during protein turnover promoted by exercise.
Muscle Growth and Hormonal Regulation
Growth Hormone
Growth hormone (HGH or hGH) is the most abundant hormone produced by the
pituitary gland. HGH is the largest and most complex protein created by the pituitary
gland. It is made up of 191 amino acids. Releasing hormones secreted from the
hypothalamus control growth hormone secretion. Growth hormone releasing hormone
(GHRH) stimulates GH release from the anterior pituitary, while hypothalamic
somatostatin inhibits it.
growth hormone (HGH or hGH): A hormone secreted by the pituitary gland that
affects skeletal growth rate and bodily weight gain.
rowth hormone secretion reaches its peak in the body during adolescence. This secretion
helps to stimulate our bodies to grow as evidenced by rapid growth spurts during
adolescence. HGH secretion does not stop after adolescence. Additional influences like
exercise, stress, a low plasma-glucose concentration and sleep can affect the secretion of
growth hormone as well.
Growth hormone stimulates tissue uptake of amino acids, the synthesis of new protein,
and long bone growth. Growth hormone also spares plasma glucose by opposing the action
of insulin to reduce the use of plasma glucose, increasing the synthesis of new glucose in
the liver (gluconeogenesis), and increasing the mobilization of fatty acids from adipose
tissue. Anything that goes on in your body is in some way tied to growth hormone,
therefore earning growth hormone the reputation as being the “fountain of youth.”
As previously mentioned, natural growth hormone secretion reaches its peak in
adolescence. The body must continue to produce growth hormone to function. But every
year after turning 20, the body produces less and less growth hormone. At 20 years old,
people average 500 micrograms of GH per day. That level drops to 200 micrograms by age
40, and by age 80 the GH levels drop to 25 micrograms per day. One theory to explain this
decrease is that somatostatin levels increase and, as mentioned earlier, hypothalamic
somatostatin inhibits growth hormone secretion.
Inevitably, given the following characteristics, especially protein synthesis, bodybuilders
would be drawn to its use and subsequent abuse. In an unfortunate drive to take
advantage of the muscle-growth-stimulating effects of growth hormone, many
bodybuilders as well as other athletes are injecting the now readily available human
growth hormone. As mentioned earlier, evidence exists that GH increases protein
synthesis in muscle; however, connective tissue protein (collagen) is increased more than
contractile protein. Consistent with these observations is the fact that strength gains do
not parallel gains in muscle size. Any time you introduce a foreign hormone into the body,
a risk of side effects exists. Chronic use of GH may lead to diabetes, carpal tunnel
compression, muscle disease, gynecomastia (overdeveloped breasts in men), and a
shortened life span.
Thyroid Hormones
The anterior pituitary is sometimes referred to as the “master gland,” because of all the
important hormones it produces. The anterior pituitary releases a substance called
thyroid-stimulating hormone (TSH). Located in the neck, the thyroid gland releases two
hormones, thyroxine (T4) and triiodothyronine (T3). The T4 hormone raises the metabolic
rate of all cells by as much as four times, greatly facilitating carbohydrate and fat
metabolism. It is believed that over the course of time, careful eating and exercise patterns
can increase your metabolic rate by calibrating the body’s “set point.”
Adrenal Hormones
The adrenal glands are comprised of two parts: the cortex (outer layer) and the medulla
(core). These glands produce hormones that enable the body to deal with stress from
physical, emotional, or psychological sources. Exercise dramatically increases output
of epinephrine, which in turn causes increased blood flow to working muscles, enhanced
cardiac output, the mobilization of energy substrate, glycogenolysis, fat mobilization, and
other functions that prepare the body to handle stress.
epinephrine: A hormone produced by the adrenal gland that causes the flight-or-fight
response.
The cortex releases a group of hormones called the adrenocortical hormones, also called
corticosteroids. This group is made up of mineralocorticoids, glucocorticoids, and
androgens. Mineralcorticoids are a group of hormones; the main hormone in this group is
aldosterone.
Aldosterone regulates the re-absorption of sodium in the distal tubules of the kidneys.
High levels of aldosterone cause sodium in the kidneys to be reabsorbed into the blood
instead of being excreted with the urine. Low aldosterone, on the other hand, causes
sodium to be excreted in large amounts through the urine. Therefore aldosterone is
responsible for controlling sodium balance in your body, and it directly impacts on
whether you retain water in the interstitial spaces (the spaces in the tissue that are outside
the blood vessels).
distal tubule of the kidney: A twisted, tube-like structure found inside a part of the
kidney known as the nephron.
High aldosterone causes a rise in extracellular fluid. This condition causes an increase in
blood volume, which in turn causes increased cardiac output and blood pressure. During
exercise, there is a constriction of blood vessels to the kidneys, so the kidneys are forced to
release an enzyme called renin into the bloodstream. Renin then stimulates the release of
yet another kidney enzyme called angiotensin, which stimulates the adrenal cortex to
release aldosterone.
Another corticosteroid, cortisol, is of interest in regard to training efforts. Cortisol is
catabolic, which means it causes a breakdown of protein in muscles. Increased cortisol
secretion also acts as an insulin antagonist by inhibiting glucose uptake and utilization.
cortisol: A corticosteroid that causes a breakdown of protein in muscles.
High cortisol levels cause the liver to split the fat molecules that are mobilized by way of
cortisol activity into ketoacids. High levels of ketoacids in the extracellular fluid can cause
a dangerous situation called ketosis to persist. This occurrence is common among people
who have been on a carbohydrate-restricted diet, such as before a bodybuilding contest or
to make weight in a particular sport.
ketosis: An abnormal increase of ketone bodies in the body; usually the result of a lowcarbohydrate diet, fasting, or starvation.
CONCLUSION
This unit has described the way the human body is organized, the 10 principal systems of
the human body, and how exercise positively affects all of these body systems. You have
learned a few of the physiological benefits of exercise from the perspective of anatomy: It
increases blood volume, enlarges blood vessels, increases the number of blood vessels,
lowers resting heart rate, improves minute volume, and helps keep blood linings clear of
corrosive materials. Exercise also reduces peak levels of hyperacidity and its discomforts,
such as ulcers. You learned about the three roles of the nervous system: It senses changes
inside and outside the body, it interprets those changes, and it responds to the
interpretations by initiating action in the form of muscular contractions or glandular
secretions. The nervous system is so complex that it is not advised to tamper with its
mechanisms.
Key Terms
adrenal glands
aerobic
afferent system
alveoli
anaerobic
autonomic system
central nervous system (CNS)
circulatory system
columnar epithelium
contraction
cortisol
cuboidal epithelium
diastolic pressure
digestion
digestive system
distal tubule of the kidney
efferent system
endocrine system
epinephrine
erythrocyte
fat metabolism
fatty acid
fructose
glandular epithelium
glucagon
gluconeogenesis
glucose
glycogen granule
glycogenolysis
glycolysis
growth hormone (HGH or hGH)
hemoglobin
insulin
integumentary system
ketosis
law of gaseous diffusion
left ventricle ejection fraction
leukocyte
ligament
lipogenesis
lymphatic system
macronutrients
maximal oxygen uptake ( O2 max)
maximum heart rate (HR max)
maximum minute volume
muscular system
nerve impulse
nervous system
nervous tissue
osmosis
peripheral nervous system (PNS)
plasma
platelet
reproductive system
residual volume
respiratory system
resting heart rate
skeletal system
somatic system
squamous epithelium
stroke volume
sympathetic nervous system
tendon
tissue
triglycerides
urinary system
vital capacity
Unit Summary
Anatomy is the science of body structure. Physiology is the science behind how our body
functions.
The biological response is the initial reaction to stress on our body. The training effect is
our body’s response to learned and expected stress. The net result is the ability to perform
activities more easily with less noticeable biological reaction resulting in increased quality
of life.
I. The human body consists of levels. Chemicals make up cells, cells associate to form
tissues, tissues function together in body systems, and these body systems make up the
human body.
A. Cells form the fundamental units of life.
1. Cellular components include the plasma membrane, nucleus, ribosomes, endoplasmic
reticulum, Golgi apparatus, lysosome, and mitochondria.
B. Tissues are the fundamental units of function and structure for the human body.
1. Tissues are defined as the aggregation of cells which are bound and work together to
perform a common function and are classified as epithelial tissue, connective tissue,
muscle tissue, and nervous tissue.
C. The body can be divided into ten main body systems: integumentary system, skeletal
system, muscular system, nervous system, endocrine system, circulatory system (of which
the lymphatic system and cardiovascular systems are subsystems), respiratory system,
digestive system, urinary system, and reproductive system.
1. The respiratory system consists of the lungs and air passageways leading to and from the
lungs, mouth, throat, trachea, and bronchi. The respiratory system supplies oxygen,
eliminates carbon dioxide, and helps regulate the pH balance of the body.
2. The circulatory system serves as the transportation system of the body. The heart,
arteries, and veins are part of this system. The circulatory system consists of two
subsystems: the cardiovascular system and the lymphatic system.
a. In the cardiovascular system, the heart pumps blood through a vast system of blood
vessels. Blood has four main constituents: plasma, erythrocytes, leukocytes, and platelets.
b. The heart tissue is mostly muscle. Unlike the lungs, the heart does its own work. The
heart takes oxygen-laden blood from the lungs and pumps it throughout the body. Carbon
dioxide-laden blood is taken back from the body and pumped into the lungs where it is
exchanged for more oxygen.
3. The digestive system consists of the digestive tract and glands that secrete digestive
juices into the digestive tract. It is responsible for the breakdown of foods and waste
elimination.
a. The components of the digestive system are the mouth, esophagus, stomach, small
intestine, large intestine, rectum, pancreas, liver, and gallbladder.
4. The nervous system is the body’s control center and network for internal
communication. A skeletal muscle cannot contract until it is stimulated by a nerve
impulse.
5. The endocrine system works with the nervous system to maintain the steady state of the
body. The endocrine system helps regulate growth, reproduction, use of nutrients by cells,
salt and fluid balance, and metabolic rate. The nervous system is also important in stress
regulation. The endocrine system consists of tissues and glands that secrete chemical
messengers called hormones.
a. Hormones are made up of amino acids and can be divided into several classes based on
their chemical makeup. The classifications are: amino acid derivatives, peptides/protein,
and steroids.
i. Insulin increases cellular uptake of glucose. Glucagon performs the opposite function of
insulin. Together, they stimulate blood sugar levels in the body.
ii. Growth hormone (HGH or hGH) is the most abundant hormone produced by the
pituitary gland. HGH is the largest and most complex protein created by the pituitary
gland.
b. The thyroid gland, located in the neck, releases two hormones: thyroxine (T4) and
triiodothyronine (T3).
c. Your adrenal glands are comprised of two parts: the cortex (outer layer) and the medulla
(inner).
UNIT 3
MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY
Paul O. Davis, PhD, FASCM with portions by Frederick
C. Hatfield, PhD
TOPICS COVERED IN THIS UNIT
Defining the Musculoskeletal System
Skeletal System
Bones
Joints
Connective Tissue
Muscular System
Types of Muscle Tissue
Reference Positions
Muscle Terminology
Structure and Function of Muscle
Neuromuscular Concepts
Adaptations to Training
Aerobic Adaptations
Anaerobic System Changes
Muscle Hypertrophy
Controversial Theories
Conclusion
Unit Outline
I. Defining the Musculoskeletal System
II. Skeletal System
A. Bones
B. Joints
C. Connective Tissue
1. Tendons
2. Ligaments
3. Cartilage
4. Connective Tissue Adaptations
III. Muscular System
A. Types of Muscle Tissue
1. Cardiac Muscle Tissue
2. Smooth Muscle Tissue
3. Skeletal Muscle Tissue
B. Reference Positions
C. Muscle Terminology
D. Structure and Function of Muscle
1. Mechanics of Muscle Contraction
2. Muscle Fiber
a. Arrangement of Muscle Fiber
b. Types of Muscle Fiber
c. Size Principle of Fiber Recruitment
E. Neuromuscular Concepts
1. All-or-None Theory
2. Stretch Reflex
IV. Adaptations to Training
A. Aerobic Adaptations
B. Anaerobic System Changes
C. Hypertrophy
D. Controversial Theories
V. Conclusion
Learning Objectives
After completing this unit, you will be able to do the following:



Know the basics about bones, joints, and connective tissue and their relationship to
exercise.
Site the names, locations, and functions of the major muscles of the body.
Understand the effects of physical training on the musculoskeletal system and apply this
knowledge to training your clients.
DEFINING THE MUSCULOSKELETAL SYSTEM
All of the systems of the body contribute to its dynamic, delicately balanced state.
Movement of the body is contingent on the interaction of the muscular system and the
skeletal system. These two systems are commonly referred to as one musculoskeletal
system, which consists of bones, joints, connective tissue, and muscles.
musculoskeletal system: Body system that consists of the bones, joints, connective
tissue, and muscles.
Muscles alone do not move weights. Rather, they move the bones that rotate about
connective tissue. Bones provide structural support, and muscles have the ability to
convert chemical energy into mechanical energy. Joints transmit forces through the bones
of the body to the external environment. This unit introduces you to the components of the
musculoskeletal system, describes their structure and function, and explains their
relationship to physical activity.
SKELETAL SYSTEM
The average human adult skeleton has 206 bones joined to ligaments and tendons to form
a supportive and protective framework for underlying soft tissues and muscles. The
skeletal system serves these important functions in the body:
skeletal system: System of the body consisting of bone and cartilage that supports and
protects the body.
1.
2.
3.
4.
Bones serve as levers that transmit muscular forces.
The skeletal system protects the body’s organs.
The skeletal system serves as a structural framework for other tissues and organs.
Bones serve as banks for storage and release of minerals, such as calcium and
phosphorous.
Figure 3.1 The skeletal system
Figure 3.2 The structure of bone
The human skeleton consists of the axial and appendicular skeleton. The axial
skeleton forms the central axis of the body and is mostly concerned with maintaining the
structure of the body. It consists of 80 bones, including the skull, spine, ribs, and sternum.
The appendicular skeleton supports the body’s appendages and is mostly concerned
with creating locomotor and manipulative movement. It consists of 126 bones—60 in the
upper extremities, 60 in the lower extremities, 2 in the pelvic girdle, and 4 in the shoulder
girdle.
axial skeleton: Bones consisting of the skull, spine, ribs, and sternum.
appendicular skeleton: Bones consisting of the upper and lower extremities, including
the pelvic and shoulder girdles.
BONES
Each of these 206 bones consists of three layers: bone marrow, compact bone, and
periosteum. Bone marrow is located in a central cavity within the long bone. Red bone
marrow produces red blood cells (which carry oxygen), white blood cells (which fight
infection), and platelets (which help stop bleeding). Yellow bone marrow primarily stores
fat cells. Surrounding the marrow is a dense, rigid bone called the compact bone.
Cylindrical in shape, the dense layers of the compact bone are honeycombed with
thousands of tiny holes and passages. Nerves and blood vessels run through these
passages, supplying oxygen and nutrients to the bone. This dense layer of compact bone
supports the weight of the body and is comprised mainly of calcium and minerals. Each
bone is covered by the periosteum, which is a layer of specialized connective tissue that
acts as the “skin” of the bone. The inner layer of the periosteum contains cells that produce
bone. These three bone layers work together to handle the aforementioned functions of the
skeletal system.
The 206 bones that make up the skeleton are divided into two categories: the axial
skeleton (trunk and head) and the appendicular skeleton (arms and legs). These bones
also vary in shape and size. The five main categories of bones are flat bones, short bones,
long bones, sesamoid bones, and irregular bones.
1. Flat bones provide protection and include the ilium, ribs, sternum, clavicle, and scapula.
They are usually characterized by a curved surface where it is either thick at the tendon
attachment or very thin.
2. Short bones provide some shock absorption and include carpals and tarsals. They are
usually characterized as small, cube-shaped, solid bones.
3. Long bones provide structural support and include the tibia, fibula, femur, radius, ulna,
and humerus. These bones are usually characterized by a long, cylindrical shaft with
relatively wide, protruding ends.
4. Sesamoid bones provide protection as well as improve mechanical advantage
of musculotendinous units and are included in the patella and the flexor tendons of the
toe and thumb. They are usually characterized as small bones embedded within the tendon
of a musculotendinous unit.
5. Irregular bones serve a variety of purposes in the body and include bones throughout
the spine as well as the ischium, pubis, and maxilla.
musculotendinous: Of, relating to, or affecting muscular and tendinous tissue.
Figure 3.3 Bone classification
JOINTS
A joint (also called an articulation) is formed when two bones connect. There are two
major classifications of joints: synarthrodial (with no separation or articular cavity, such
as the skull) and diarthrodial (a freely movable joint with an articular cavity).
joint: Point where two bones connect.
A diarthrodial joint has an articular cavity encased in a ligamentous capsule. Synovial
fluid lubricates the smooth cartilage inside the joint capsule. Diarthroidal joints are
synovial fluid: A fluid that lubricates the smooth cartilage in joints.
classified in six categories: arthrodial (gliding), condyloidal (biaxial ball-and-socket),
enarthrodial (multiaxial ball-and-socket), giglymus (uniaxial hinge), sellar (saddle), and
trochoidal (pivot). They are defined as follows:
1. Arthrodial (gliding) joints permit limited gliding movement and include bones of the
wrist and the tarsometatarsal joints of the foot. They are characterized by two flat, bony
surfaces that press up against each other.
2. Condyloidal (ellipsoid) joints permit movement in two planes without rotation.
Examples include the wrist between the radius and the proximal row of carpal bones and
the second, third, fourth, and fifth metacarpophalangeal joints.
3. Enarthrodial (multiaxial ball-and-socket) joints permit movement in all planes.
They include the shoulder and hip joints.
4. Ginglymus (hinge) joints permit a wide range of movement in one plane. Examples of
hinge joints are the elbow, ankle, and knee joint.
5. Sellar (saddle) joint permits ball-and-socket movement with the exception of rotation.
The thumb is the only saddle joint in the body and is capable of reciprocal reception.
6. Trochoidal (pivot) joints permit rotational movement around a long axis as with the
rotation of the radius at the radioulnar joint.
Figure 3.4 Types of joints
CONNECTIVE TISSUE
As its name suggests, the primary function of dense connective tissue is to connect muscle
to bone and to connect joints together. Comprised of fiber calledcollagen, mature
connective tissue has fewer cells than other tissues. Therefore, it needs (and receives) less
blood and the oxygen and other nutrients found in blood.
collagen: Fibrous protein that forms tough connective tissue.
Each collagen bundle is comprised of several fibers, which, in turn, contain several fibrils.
These fibrils contain the actual collagen molecules, which are triple helix in structure.
Tendons
Tendons are extensions of the muscle fibers that connect muscle to bone. They are tough
bands of connective tissue that are slightly more elastic than ligaments, but they cannot
shorten as muscles do.
tendon: The fibrous connective tissue that connects muscle to bone.
Various proprioceptors (the sensory organs found in muscles and tendons) provide
information about body movement and position, as well as protect muscle and connective
tissue. The Golgi tendon organ is embedded in tendon tissue; you can think of it as a safety
valve. Increasing levels of muscular contraction result in feedback to the nervous system
from the Golgi tendon organ. When tension becomes too great—greater than the brain can
recall—this signal inhibits the contraction stimulus, thereby reducing the likelihood of
injury. This protective response is called the feedback loop.
feedback loop: Section of a control system that serves as a regulatory mechanism; return
input as some of the output.
Figure 3.5 Feedback loop
Figure 3.6 Cartilage
Ligaments
Ligaments connect bones to bones at a joint and, along with collagen, contain a
somewhat elastic fiber called elastin. While ligaments must have some elasticity to allow
for joint movement, it is a limited amount.
ligament: The fibrous connective tissue that connects bone to bone, or bone to cartilage,
to hold together and support joints.
elastin: Elastic fibrous protein found in connective tissue.
Cartilage
Cartilage is a firm, elastic, flexible, white connective tissue. It is found at the ends of ribs,
between vertebrae (discs), at joint surfaces, and in the nose and ears. As a smooth surface
between adjacent bones, cartilage provides both shock absorption and structure. Cartilage
also lubricates the working parts of a joint. Unlike tendons and ligaments, cartilage has no
blood supply of its own. The only way for cartilage to receive oxygen and nutrients is
through diffusion (which is the movement of molecules from an area of high concentration
to an area of low concentration). Because of this lack of nutrients, damaged cartilage heals
very slowly.
cartilage: A firm, elastic, flexible, white material found at the ends of ribs, between
vertebrae (discs), at joint surfaces, and in the nose and ears.
Connective Tissue Adaptations
The positive effects of exercise on connective tissue have been well documented. Physical
training has been shown to cause an increase in tensile strength, size, resistance to injury,
and the ability to repair damaged ligaments and tendons to regular tensile strength. As
noted earlier, proper training can alter the Golgi tendon organ and “push back” the “safety
valve,” which shuts off muscle contractions. Not just any type of training alters the
structure of connective tissue. Surprisingly, much of the research done with the effects of
training on connective tissue has been done with endurance training. While endurance
training has been shown to produce some adaptations, higher-intensity training is more
likely to force these adaptations—in some cases even high-speed ballistic movements.
As with all training, ballistic movements that forces adaptations in connective tissues must
be used with care.
ballistic movements: Muscle contractions that exhibit maximum velocities and
accelerations over a very short period of time. They exhibit high firing rates, high force
production, and very brief contraction times.
MUSCULAR SYSTEM
All body movements—walking, running, and even circulating blood, among other things—
depend on the actions of muscles. Some 600 muscles work together with the support of
the skeletal system to create motion. An additional 30 or so muscles are required in order
to insure the passage of food through the digestive system, to circulate blood, and to
operate specific internal organs. In exercise physiology, muscles are the main operative
tissues; they expend energy, generate wastes, and require substantial nutrition.
TYPES OF MUSCLE TISSUE
When observed under a microscope, muscles differ in appearance because of their varying
cellular structures. Two appearances are recognized: striated muscle tissue and smooth
muscle tissue. Based on functional and structural differences, muscle tissue is divided into
three types: skeletal, cardiac, and smooth.
Cardiac Muscle Tissue
Cardiac muscle tissue (striated-involuntary muscle tissue) composes the wall of the heart.
It functions to contract the heart and pump blood through body. Cardiac muscle cells are
often branched, and their nuclei are more centered than with skeletal muscle cells. They
have a tendency to branch and fuse into each other. Fortunately, cardiac muscle tissue
does not fatigue easily; the period of rest in between contractions is all it needs. Even
during periods of intense exercise, it is the skeletal muscles that fatigue first.
Smooth Muscle Tissue
Smooth muscle tissue (smooth involuntary muscle tissue) is found in walls of the tubular
viscera of digestive, respiratory, and genitourinary tracts; in walls of blood vessels and
large lymphatics; in ducts of glands; in intrinsic eye muscles (iris and ciliary body); and in
erector muscle of hairs. It functions to move substances along their respective tracts,
change diameter of blood vessels, move substances along glandular ducts, change the
diameter of pupils and shape of lens, and erect hairs. Like cardiac muscle tissue, smooth
muscle tissue cells are elongated, but differ in having pointed ends and only one nucleus
per cell. They contract more slowly than striated muscle and therefore do not fatigue
easily.
Skeletal Muscle Tissue
Skeletal muscle tissue (striated voluntary muscle tissue) is found attached to bones, in
extrinsic eyeball muscles, and in the upper third portion of the esophagus. Skeletal muscle
tissue functions to move the bones and eyes. It also moves food during the first part of
swallowing. Skeletal muscle tissue is made up of long muscle cells (muscle fibers) that bear
the unique characteristic of being multinucleate (containing many nuclei).
Characteristically, skeletal muscle tissue cannot sustain prolonged maximal-effort
contractions because they easily fatigue. The main focus of this unit is on the skeletal
muscles, which are the voluntary muscles attached to bones and therefore the prime
movers during training.
REFERENCE POSITIONS
Trainers need to develop a basic knowledge of the musculoskeletal system, its planes of
motion, joint classifications, and joint movement. The anatomical position is the most
widely used reference point for analyzing the body. In the anatomical position, the subject
is in an upright position, facing straight ahead, with feet parallel and palms facing forward.
See the following page for additional anatomical directional terminology.
Figure 3.7 Anatomical position
Table 3.1
Anatomical Directional Terminology
Anterior
In front or in the front part
Anteroinferior
In front and below
Anterolateral
In front and to the side, especially the outside
Anteromedial
In front and toward the inner side or midline
Anteroposterior
Relating to both front and rear
Caudal
Below in relation to another structure; inferior
Cephalic
Above in relation to another structure; higher, superior
Contralateral
Pertaining or relating to the opposite side
Deep
Beneath or below the surface; used to describe relative depth or
location of muscles or tissue
Distal
Situated away from the center or midline of the body, or away from
the point of origin
Dorsal
Relating to the back; posterior
Inferior (infra)
Below in relation to another structure; caudal
Ipsilateral
On the same side
Lateral
On or to the side; outside, farther from the median or midsagittal
plane
Medial
Relating to the middle or center; nearer to the medial or
midsagittal plan
Posterior
Behind, in back, or in the rear
Posteroinferior
Behind and below; in back and below
Posterolateral
Behind and to one side, specifically to the outside
Posteromedial
Behind and to the inner side
Posterosuperior Behind and at the upper part
Prone
The body lying face downward; stomach lying
Proximal
Nearest the trunk or the point of origin
Superficial
Near the surface; used to describe relative depth or location of
muscles or tissue
Superior
(supra)
Above in relation to another structure; higher, cephalic
Supine
Lying on the back; face upward position of the body
Ventral
Relating to the belly or abdomen
Volar
Relation to palm of the hand or sole of the foot
Figure 3.8 Major muscles of the human body
Figure 3.9a Upper arm
MUSCLES OF THE UPPER ARM
1.
2.
3.
4.
5.
6.
7.
Humerus (bone)
Biceps brachii (long head)
Biceps brachii (short head)
Triceps brachii (lateral head)
Triceps brachii (long head)
Triceps brachii (medial head)
Brachialis
Figure 3.9b Forearm
MUSCLES OF THE FOREARM
1.
2.
3.
4.
5.
6.
7.
Brachioradialis
Pronator teres
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris
Supinator
Flexor pollicis longus
8. Flexor digitorum profundus
9. Pronator quadratus
10.Extensor carpi radialis longus
11. Extensor carpi radialis brevis
12. Extensor digitorum
Figure 3.9c Shoulder and deltoid
MUSCLES OF THE SHOULDER
1.
2.
3.
4.
5.
6.
7.
8.
9.
Humerus (bone)
Clavicle (bone)
Supraspinatus
Subscapularis
Infraspinatus
Spine of scapula
Teres minor
Biceps brachii (long head)
Biceps brachii (short head)
MUSCLES OF THE DELTIOD
1.
2.
3.
4.
5.
Humerus (bone)
Clavicle (bone)
Anterior deltoid
Lateral deltoid
Posterior deltoid
Figure 3.9d Back
MUSCLES OF THE BACK
1.
2.
3.
4.
5.
6.
7.
Trapezius
Latissimus dorsi
External obliques
Semispinalis capitis
Semispinalis cervicis
Quadratus lumborum
Rhomboid minor
8. Rhomboid major
9. Multifidus
10.Spianlis (erector spinae group)
11. Longissimus (erector spinae group)
12. Iliocostalis (erector spinae group)
Figure 3.9e Midsection
MUSCLES OF THE MIDSECTION
1. Pectoralis major
2. Serratus anterior
3. Exernal oblique
4. Internal oblique
5. Rectus abdominis
6. Transverse abdominis
7. Linea alba
8. Linea semilunaris
9. Rectus sheath
10.Quadratus lumborum
11. Psoas
12. Erector spinae
Figure 3.9f Chest
MUSCLES OF THE CHEST
1. Pectoralis major
2. Subclavius
3. Pectoralis minor
Figure 3.9g Upper legs
MUSCLES OF THE UPPER LEG
1.
2.
3.
4.
5.
6.
Psoas
Iliacus
Gluteus medius
Gluteus minimus
Tensor fasciae latae
Sartorius
7. Adductor longus
8. Gracilis
9. Rectus femoris
10.Vastus lateralis
11. Vastus medialis
12. Gluteus maximus
13. Biceps femoris
14. Semitendinosus
15. Semimembranosus
Figure 3.9h Lower legs
MUSCLES OF THE LOWER LEG
1.
2.
3.
4.
5.
Tibialis anterior
Peroneus longus
Extensor digitorum longus
Extensor hallucis longus
Gastrocnemius
6. Soleus
7. Peroneus brevis
8. Tibialis posterior
MUSCLE TERMINOLOGY
Locating muscles and knowing their relationship to the joints is critical in understanding
the effects that they have on joints. When a muscle contracts, it tends to pull both ends
toward the belly (middle) of the muscle. If neither of the bones to which a muscle is
attached were stabilized, then both bones would move toward one another during
contraction. However, in the body, one bone is more stabilized by a variety of factors,
which results in the less stabilized bone moving during contraction. The points of
attachment are known as the insertion and the origin of the muscle.




Origin: The proximal attachment. The origin is generally considered the least movable
part or the part that attaches closest to the midline (vertical center in the anatomical
position) of the body.
Insertion: The distal attachment. The insertion is generally considered the most movable
part or the part that attaches farthest from the midline of the body.
Action(s): The specific movements that each muscle is capable of and/or responsible for
(listed in biomechanical terms).
Innervation: The specific distribution or supply of nerves to a particular part of the
body.
TRAINER FOCUS: INSERTION AND ORIGIN
Figure 3.10a Origin and insertion: upper body
Figure 3.10b Origin and insertion: rotator cuff
Figure 3.10c Origin and insertion: upper arm
Figure 3.10d Origin and insertion: quadriceps group
Figure 3.10e Origin and insertion: hamstring group
Figure 3.10f Origin and insertion: lower leg
Figure 3.10g Origin and insertion: midsection
STRUCTURE AND FUNCTION OF MUSCLE
Muscles are largely composed of protein, with a hierarchical system of organization from
large groups to small fibers. A muscle is a group of motor units that are physically
separated by a membrane from other groups of motor units. A muscle is connected to
bones through tendons. See Figure 3.11 for a diagram of muscle composition.
A motor unit consists of a single neuron and all of the muscle fibers innervated by it. The
ratio of nerves to fibers determines the fine motor control available to that muscle. For
example, the hand has fewer fibers per motor unit than do the muscles of the calf.
The muscle fiber is composed of myofibrils, which are small bundles of myofilaments.
Myofilaments are the elements of the muscle that actually shorten upon contraction.
Myofilaments are made up mainly of two types of protein, myosin (short, thick filaments)
and actin (long, thin filaments). Two other important proteins comprising myofibrils are
troponin and tropomyosin, involved in the contractile response.
myofilaments: The elements of the muscle that actually shorten upon contraction; made
up mainly of two types of protein: actin and myosin.
myosin: Short, thick contractile filaments.
actin: Long, thin contractile filaments.
The main function of muscle tissue is contraction. This contraction of muscle can be
brought about by either involuntary or voluntary stimuli. Voluntary muscle
tissues receive nerve fibers from the somatic nervous system. Therefore, their contraction
can be voluntarily controlled. Skeletal muscles are the major voluntary muscle
tissue. Involuntary muscle tissues receive nerve fibers from the autonomic nervous
system and cannot be voluntarily controlled, except in a few rare cases. The eternal pump,
the heart, is an example of an involuntary muscle tissue.
voluntary muscle tissues: Receive nerve fibers from the somatic nervous system that
can be voluntarily controlled (e.g., skeletal muscles).
involuntary muscle tissues: Receive nerve fibers from the autonomic nervous system
and cannot be voluntarily controlled, except in a few rare cases. (e.g., the heart).
Figure 3.11 Organization of human skeletal muscle
With few exceptions, single muscles never contract by themselves. Rather, specific sets of
muscles contract together or in sequence. The production of complex movements
responsible for even the simplest of tasks depends on a correspondingly subtle control
mechanism. This is the responsibility of the nervous system, which neutralizes the actions
of muscles that are not required and causes the contraction of muscles that are required.
The spinal cord and brain exercise this control through the motor nerve fibers.
Each muscle cell does not have an individual line from the central nervous system (CNS).
Impulses travel down the nerve axon from the CNS, branching off to supply a group of
muscle cells that contract together. In order to coordinate muscular movement, the CNS
must be supplied with information about the length of the muscle and the tension of the
tendons, which attach it to the skeleton. This information is provided by special sense
organs called muscle spindles, that measure the strain in the muscle and can be used to
preset the tension of muscles.
muscle spindles: Sensory receptors within the belly of a muscle that primarily detect
changes in the length of this muscle. Measures and delivers the quantity of muscle force
needed to perform a given action.
Skeletal muscles must contract rapidly in response to signals from the CNS, and they must
develop adequate tension at the same time in order to produce an effective mechanical
force. Examination of skeletal muscle reveals a junction between the nerve fiber and the
muscle surface. The surface acts as an amplifier, increasing the effect of the tiny current
coming down the nerve fiber to stimulate the larger muscle fiber. The arrival of the nerve
impulse triggers the release of a chemical called acetylcholine from the motor nerve
ending. This passes across the gap to stimulate the membrane
of muscle fiber. This stimulation, in the form of an electric current, passes along the
surface of the muscle and causes it to contract. It takes only one thousandth of a second for
the current to pass along the surface of the muscle fiber. The fiber releases unless yet
another impulse arrives. If this chemical mechanism were blocked, the result would be
paralysis.
Mechanics of Muscle Contraction
To the naked eye, the external skeletal muscles appear grainy because they are made up of
small fibers. These fibers are cylinder-like and may be several centimeters long. In length,
they are divided into bands (striations), much like coins stacked in a pile. Each individual
fiber is surrounded by a thin plasma membrane: the sarcolemma. Some 80 percent of the
fiber’s volume is filled with tiny fibrils, known as myofibrils, which may number from
several hundred to several thousand per fiber. These fibrils are the structures, which are
directly involved in contraction of the muscle fiber. The remainder of the muscle fiber is
filled with a jellylike intracellular fluid called sarcoplasm. The sarcoplasm contains many
nuclei and other cell constituents, such as mitochondria, within which energy-producing
biochemical reactions take place.
myofibrils: Tiny fibrils that make up a single muscle fiber.
sarcoplasm: Jellylike intracellular fluid found in the muscle fiber.
Further examination of the fibrils has revealed that they are made of two types of protein—
actin and myosin—which are in the form of long filaments. The thick ones consist of
myosin and the thin ones are made of actin. These filaments are able to interlock and slide
over each other to accommodate the stretching of the muscle. During shortening
(contraction), they slide into one another and it appears that cross-links are made between
the actin and myosin filaments. These cross-links are almost instantaneously broken and
new links are set up further along the filaments. The process of breaking these cross-links
causes the two filaments to move toward one another, causing the muscle to shorten
(contraction). This process is known as the sliding filament theory.
sliding filament theory: Theory stating that a myofibril contracts by the actin and
myosin filaments sliding over each other.
Figure 3.12 Muscle cross section
Figure 3.13 Structural rearrangement of actin and myosin myofilaments while fully
stretched, at rest, and contracted
The sliding filament theory states that a myofibril contracts by the actin and myosin
filaments sliding over each other. Chemical bonds and receptor sites on the myofilaments
attract each other, allowing the contraction to be held until fatigue interferes (see Figure
3.13). The strength of contraction in a gross muscle depends, in large part, upon the
number of muscle fibers involved: The more muscle fibers, the stronger the contraction.
The term “contraction” does not always refer to the shortening of a muscle. Technically, it
refers to the development of tension within a muscle. Mainly two contractions occur in the
muscle. A contraction in which the muscle develops tension but does not shorten is
called isometric. A contraction in which the muscle shortens but retains constant tension
called isotonic. For example, a person trying to curl a heavy barbell strains against the
weight. The arm muscles develop tension but do not shorten, because the amount of
resistance generated by the heavy barbell is greater than the muscle’s tension. If plates are
removed, the load is lightened and the working muscles shorten as they contract. This is
an isotonic contraction. When muscles shorten by overcoming resistance to a load
(weight), the isotonic contraction is said to be concentric. When the biceps lengthen
while the barbell is let down but they maintain a constant tension during the lengthening
movement, this type of isotonic contraction is termed eccentric. The muscles lengthen as
they act to maintain tension.
isometric: A contraction in which the muscle develops tension but does not shorten.
isotonic: A contraction in which the muscle shortens but retains constant tension.
concentric: A contraction in which a muscle shortens and overcomes a resistance.
eccentric: A contraction in which a muscle lengthens and is overcome by a resistance.
The energy for contraction is derived from the chemical reaction between the food
components consumed and the oxygen breathed. Therefore, blood is needed in order to
bring the essential nutrients and oxygen to the muscles and remove waste products. The
biochemical process of energy production involves the breakdown of glucose (fatty acids or
fructose) to eventually just carbon dioxide and water. This breakdown releases the energy
used by muscle proteins to cause contraction. This specific chemical reaction requires an
abundant supply of oxygen, which is often unavailable. Even during intense exercise, the
blood supply is often insufficient to carry enough oxygen to the muscles. The muscles solve
this problem by converting glucose into lactic acid, without oxygen, which still gives an
ample release of energy.
lactic acid: A byproduct of glucose and glycogen metabolism (glycolysis) in anaerobic
muscle energetics.
Lactic acid accumulation, however, limits the intensity with which the body can exercise
muscles. Ultimately it prevents continuation of the exercise at the same intensity; fatigue
prevails. The excess lactic acid eventually enters the bloodstream and is circulated to the
liver, where it can be reassembled into glucose and returned into the bloodstream or
stored as glycogen. Some of the lactic acid can also be converted back into the molecule
pyruvic acid and enter into the mitochondria to be completely broken down for energy.
Figure 3.14 Skeletal muscle contraction
Muscles (and other tissues) store glucose in a form of complex carbohydrate called
glycogen. The body calls upon this storehouse of energy during a high-intensity, lowduration activity such as weightlifting (as opposed to caloric draw during a low-intensity,
high-duration activity such as long-distance running, which uses a mixture of glucose from
glycogen and fatty acids from fat stores).
Muscle Fiber
When muscle fibers contract, they have the ability to generate force. Their alignment,
general type, and stimulus for recruitment have an effect on this forge-generating ability.
Arrangement of Muscle Fiber
The alignment of the muscle fibers has a distinct effect on their ability to generate force.
Fusiform arrangement occurs when the fibers are parallel to the tendons and therefore can
contract at great speeds with a loss in total force output. A unipennate muscle has fiber
alignment going from one side to the other in regards to the tendon while a bipennate
muscle has alignment of fibers on both sides of the muscle. Muscles with a unipennate,
bipennate, or multipennate arrangement are capable of producing higher amounts of force
than a fusiform arrangement can, but at the expense of contractile velocity. It is believed
that fiber arrangement is determined by genetics; however, it may be altered somewhat
with training.
pennate: A muscle in which fibers extend obliquely from either side of a central tendon
fast-twitch: Muscle fiber type that contracts quickly and is used mostly in intensive,
short-duration exercises.
Figure 3.15 Muscle fiber arrangements
Types of Muscle Fiber
Skeletal muscle tissue is composed of two general types of muscle fibers: fasttwitch and slow-twitch. Fast-twitch fibers are selectively recruited when heavy
workloads are demanded of the muscles and strength and power are needed. They are
recruited for high-intensity, short-duration work. They contract quickly, yielding short
bursts of energy, and they are recruited in high numbers during brief, intense exercises
such as sprinting, weightlifting, shot putting, or even swinging a golf club. But these fasttwitch muscle fibers exhaust quickly. Pain and cramps settle in rapidly as they become
vulnerable to lactic acid buildup, a byproduct of their own metabolism.
slow-twitch: A muscle fiber characterized by its slow speed of contraction and a high
capacity for aerobic glycolysis.
Slow-twitch muscle fibers produce a steadier, low-intensity, repetitive contraction that is
characteristic of endurance activities. They are capable of sustaining workloads of low
intensity and long duration, such as long-distance running. Athletes of high-intensity
sports, such as weightlifting, wrestling, and sprinting, tend to have a greater percentage of
fast-twitch muscle fibers. Athletes of low-intensity sports, such as longdistance running,
tend to have a higher percentage of slow-twitch muscle fibers.
Three distinct types of muscle fiber are found in skeletal muscle: Type I are slow-twitch
fibers, and Type IIa and Type IIx are fast-twitch fibers (see Table 3.3). The
type I: A slow-twitch muscle fiber that generates ATP predominantly through the aerobic
system of energy transfer.
type IIa: A fast-twitch fiber subdivision characterized by a fast shortening speed and
well-developed capacity for energy transfer from aerobic and anaerobic sources.
type IIx: A fast-twitch fiber subdivision characterized by the most rapid shortening
velocity and greatest anaerobic potential.
percentage of each varies from person to person and from one muscle to another in the
same person. Type I muscle fibers (slow-twitch, red fiber) are highly resistant to fatigue
and injury, but their force output is very low. Activities that are performed in the aerobic
pathway call upon these muscle fibers. Type IIa muscle fibers (fast-twitch, intermediate
fibers) are larger in size and much stronger than Type I fibers. They have a high capacity
for glycolytic activity; they can produce high force output for long periods. Type IIx muscle
fibers (fast-twitch muscle fibers) are often referred to as “couch potato fibers” because of
their prevalence in people who are sedentary. Research has shown that 16 percentof a
sedentary person’s total muscle mass is of this fiber type. It has been hypothesized that
Mother Nature gave deconditioned folks these explosive fibers so that they could cope with
emergency situations.
Type IIx fibers are extremely strong, but they have almost no resistance to fatigue or
injury. In fact, they are so strong and susceptible to injury that when they are used, they
often are damaged beyond repair. Unless the body can repair the muscle cell, it is broken
down and sloughed off into the amino acid pool. In most cases, sedentary people
immediately lose their Type IIx fibers when beginning a training program.
A fourth type of fiber (Type IIc) is the result of Type IIx fibers fusing with surrounding
satellite cells. As noted earlier, Type IIx fibers are destroyed when they are used because of
their fast-twitch capacity and poor recovery ability. When muscle fibers are damaged from
training stress, a highly catabolic hormone called cortisol is released to facilitate the
“cleanup” operation. If cortisol is blocked, however, the Type IIx fibers fuse with
surrounding satellite cells (noncontractile muscle cells, which help support or bulwark the
tenuous IIb fibers). The result of the fusion is a Type IIc fiber. Insulin-like growth factor1
(IGF-1) stimulates the fusion process. Professional bodybuilders have learned how to
facilitate this process in order to achieve greater muscle hypertrophy. The implications of
fusion for other individuals are discussed later in this text.
type IIc: A fast-twitch fiber that results from the “fusion” of Type IIx with surrounding
satellite cells.
Fast-twitch fibers are serviced with thicker nerves, giving them a greater contractile
impulse (measured in number of twitches per second). Slow-twitch fibers have smaller
nerves (thus twitch fewer times per second), but they have a high degree of oxygen-using
capacity stemming from the greater number of mitochondria (the cells’ “powerhouses,”
where ATP is synthesized) and a higher concentration of myoglobin and other oxygenmetabolizing enzymes.
Size Principle of Fiber Recruitment
Force output of muscle is related to the stimulus it receives. Recalling from Table 3.3,
different muscle fibers have different liability to recruitment; Type I fibers have the
highest liability, Type IIa and IIc have a moderate liability, and Type IIx have a low level of
liability. The size principle of fiber recruitment (also called the Henneman
principle) states that fibers with a high level of liability are recruited first, and those with
lower levels of liability are recruited last. According to the size principle, motor units are
recruited in order according to their recruitment thresholds and firing rates. Since most
muscles contain a range of Type I and Type II fibers, force production can be very low or
very high. Therefore, to get to a high-threshold motor unit, all of the motor units below it
must be sequentially recruited. Picking up the phone versus curling a 75-pound dumbbell
exemplifies this principle. The lower-threshold motor units are recruited to pick up the
phone while the higher-threshold motor units are recruited to curl a 75-pound dumbbell.
size principle of fiber recruitment: Principle stating that motor units are recruited in
order according to their recruitment thresholds and firing rates.
NEUROMUSCULAR CONCEPTS
All-or-None Theory
When a nerve carries an impulse of sufficient magnitude down to the muscle cells that
comprise the motor unit, the myofibrils do the only thing they know how to do—contract.
Each myofibril does not do this by degrees, but rather it contracts totally. It responds with
an all-or-none reaction. In other words, a unit is either completely relaxed or fully
contracted; it is never partly contracted. A muscle fiber (including myofibrils) and its
corresponding motor unit respond to a nerve stimulus with the all-or-none reaction.
all-or-none reaction: Concept stating that a unit is either completely relaxed or fully
contracted; it is never partly contracted.
However, not all of the motor units comprising a muscle are activated during any given
movement. You are able to exercise a gradation of response by increasing or decreasing
the amount of chemoelectrical impulse to the muscle. That’s why you can lift a fork to your
mouth or curl a heavy dumbbell. Both are similar movements, but curling a fork involves
only those motor units with a very low excitation threshold; curling the dumbbell requires
many more motor units.
Stretch Reflex
The stretch reflex is a built-in protective function of the neuromuscular system in the
muscle spindle, a proprioceptor found in the belly of a muscle. In contrast to the Golgi
tendon organ, which is in series with the force plane of the muscle, the muscle spindle is in
parallel with the force plane. The action is similar to that of the Golgi tendon organ in that
it protects against overload and injury in what is known as the stretch reflex action
(example: the knee-jerk response used by physicians to test your muscle’s response
adequacy).
stretch reflex: A built-in protective function of the neuromuscular system in the muscle
spindle.
proprioceptor: Specialized sensory receptors located in tendons and muscles sensitive
to stretch, tension, pressure, and position of the body. Proprioceptors include muscle
spindles and Golgi tendon organs.
The stretch reflex serves as a regulatory mechanism that enables the muscle to adjust
automatically to differences in load and length without having to receive messages from
higher-order centers (your brain) of the nervous system. Other proprioceptors are located
in and around all the joints of the body. These sensors provide constant information to the
nervous system regarding the special relationship of the joint to the rest of the body in
terms of movement, position, and speed, among other factors.
Figure 3.16 Knee jerk reaction
ADAPTATIONS TO TRAINING
Exercise stimulates a series of metabolic responses that affect the
body’s anatomy, physiology, and biochemistry. The magnitude of changes is driven
primarily by whether the exercise is anaerobic or aerobic. The type and duration of
exercise physically stimulate muscles to develop more fast- or slow-twitch muscle fibers,
and in turn dictate the primary energy mix used. High-intensity exercise simulates fast-
twitch muscle fiber development, while low-intensity exercise results in slow-twitch
muscle fiber development. In addition, a series of hormonal changes occur on an overall
basis during periods of exercise and periods of nonexercise. These changes also are
benefited and facilitated with a nutrient profile that matches the type of metabolic flux.
anatomy: The science of the structure of the human body.
physiology: The science concerned with the normal vital processes of animal and
vegetable organisms.
biochemistry: the branch of science concerned with the chemical and physicochemical
processes that occur within living organisms.
AEROBIC ADAPTATIONS
Aerobic exercise, whether it is aerobic endurance training or some form of cardiovascular
work on a treadmill, stepper, or bike, has numerous benefits, including fat burning,
enhancement of cardiovascular health, and improved recovery abilities. Many trainees
may stay away from aerobic exercise fearing that it will result in muscle loss. This muscle
loss is usually a direct result of an inadequate supply of calories to sustain the aerobic
work rather than the aerobic exercise itself. For example, a bodybuilder who loses muscle
during a period of aerobic training is not eating enough to compensate for the calories
expended.
aerobic: Occurring with the use of oxygen, or requiring oxygen.
Aerobic exercise forces oxygen through the body, increasing the number and size of the
blood vessels. Blood vessels transport oxygen and nutrients to muscles and carry waste
products away for muscular growth, repair, and recovery. Without aerobic exercise in the
training program, the body cannot create any new supply routes for newly developed
muscles. Type I fibers are said to possess an oxidative capacity greater than that of Type II
fibers both before and after training. Whereas strength and hypertrophy training produce
somewhat similar muscular adaptations, aerobic training adaptations are different. A
gradual conversion of Type IIx fibers to Type IIa fibers may occur. This type of adaptation
is significant because Type IIa (fast oxidative glycolytic) fibers possess a greater oxidative
capacity than Type IIx (fast glycolytic) fibers, as well as being more similar
characteristically to Type I fibers. The result is a greater number of muscle fibers that can
contribute to endurance performance.
Some important metabolic changes take place inside the body through aerobic training.
First at the cellular level, aerobic exercise adaptations include an increase in the size and
number of mitochondria and greater myoglobin content. Mitochondria (cellular “furnaces”
where fat and other nutrients are burned) are the organelles in cells that are responsible
for aerobically producing ATP by way of oxidation of glycogen. When the larger and more
prevalent mitochondria are combined with an increase in the quantity of oxygen that can
be delivered to the mitochondria through higher levels of myoglobin, the aerobic capacity
of the muscle tissue is enhanced.
Second, aerobic exercise appears to increase levels of myoglobin. Myoglobin is a protein
that transports oxygen from the bloodstream into the muscle fibers. Finally, this
adaptation increases the level and activity of the enzymes involved in the aerobic
metabolism of glucose. Larger mitochondria in greater numbers, increased levels of
aerobic enzymes, coupled with increased blood flow all boost the fat burning capabilities of
the muscle fibers.
ANAEROBIC SYSTEM CHANGES
Anaerobic training greatly increases the body’s functional capacity for development of
explosive strength and maximization of short-term energy systems. Some of the major
changes measured as a result of anaerobic exercise include an increased size and number
of fast-twitch muscle fibers. In addition, anaerobic work results in an increased tolerance
to higher levels of blood lactate, an increase in enzymes involved in the anaerobic phase of
glucose breakdown (glycolysis), and an increase in muscle resting levels
of ATP, CP, creatine, and glycogen content. Finally, anaerobic changes include an
increase in growth hormone and testosterone levels after short bouts (45–75 min) of highintensity weight training. Growth hormone, testosterone, insulin, and insulin-like growth
factor are the four hormones that are directly responsible for muscle hypertrophy, which is
discussed next.
anaerobic: Occurring without the use of oxygen.
adenosine triphosphate (ATP): An organic compound found in muscle which, upon
being broken down enzymatically, yields energy for muscle contraction
creatine phosphate (CP): A high-energy phosphate molecule that is stored in cells and
can be used to immediately resynthesize ATP.
creatine: Organic acid generally found in the muscle as phosphocreatine that supplies
energy for muscle contraction.
MUSCLE HYPERTROPHY
Muscle hypertrophy is an important consideration in training for many reasons. The first
is that when a person trains, the intensity and duration of training influence the
physiology of muscle tissue and development of muscle fibers. The long-distance runner
tends to develop slow-twitch muscle fibers, while the powerlifter tends to develop fasttwitch muscle fibers. One reason the fast-twitch muscle fibers increase in size is to
increase the storage capacity for more adenosine triphosphate and creatine phosphate
(ATP and CP). ATP and CP are needed for explosive energy that lasts only a few seconds.
The second reason is that the physiological conditioning of muscle tissue determines
which fuel source is used. Power athletes need more muscle glycogen to fuel their muscles,
while endurance athletes need both muscle glycogen and fatty acids.
Muscle hypertrophy is simply the increase in the size of muscle fibers. Muscle fibers
increase in size in response to adaptive overload stress. Adaptation takes place in several
ways. The principal mechanism for muscular hypertrophy is by individual muscle cells
increasing the number of their myofibrils. This probably occurs as a result of increased
amino acid transport into the cells (caused by tension), which enhances their
incorporation into contractile protein. However, muscle hypertrophy also occurs as a
result of proliferation (in size and number) of mitochondria, myoglobin (storage protein),
extracellular and intracellular fluid, capillarization (tiny blood vessels surrounding
cells), and fusion between muscle fibers (principally Type IIx) and surrounding satellite
cells.
hypertrophy: An increase in the cross-sectional size of a muscle in response to strength
training.
capillarization: An increase in size and number of tiny blood vessels surrounding cells.
In addition to increasing the size of the muscle fibers, increasing the number of muscle
fibers also seems to be a logical mechanism of muscle growth. Researchers have reported
the possibility of fiber splitting in their research reports (longitudinal division of muscle
fibers resulting in new muscle cells). But some researchers have criticized the methodology
used in their studies, and the issue remains unresolved, probably until visual evidence of
the phenomenon is available. Healthy weight gain programs should promote increases in
muscle mass (hypertrophy) and only increase body fat mass to the correct percentage for
health and performance. Section 5 includes more detailed discussion on the nutrition
aspect of healthy weight gain.
CONTROVERSIAL THEORIES
One of the more controversial theories of muscle adaptation focuses on changes in fiber
type distribution. Whether one muscle fiber type can change to another has been shown in
certain studies but not in others. Furthermore, sport scientists have often argued whether
changes take place or merely a fiber takes on different characteristics closer to another
fiber type.
Several studies have suggested that a Type II fiber can change to or take on characteristics
of a Type I fiber with increased endurance activity. This seems highly reasonable in that
endurance training has been shown not to increase (and may even decrease) the amount
and size of heavy-chain myosins as well as increase mitochondrial density. With this
training, even the powerful Type II fibers will decrease in maximal power output.
It is also widely held that Type I fibers cannot change to Type II fibers. However, studies
have shown that in training above the anaerobic threshold, Type I fibers decreased while
Type II (especially Type IIc) increased. Rival studies suggest that in such training, an
increase in Type II fiber area is possible, as opposed to actual fiber conversion.
Type IIx to Type IIa or IIc fiber conversion is also a possibility (as discussed earlier in this
unit). Studies have shown that untrained subjects have 16 percent of their total muscle
mass in Type IIx fiber type. However, after 1 week of training, this 16 percent disappeared.
Other studies have shown that Type IIx fiber distribution decreases with training while
Type IIa distribution increases (with little change in Type I or IIc). Not many studies have
specifically looked at Type IIx or Type IIc fibers. However, if such Type IIx fiber
conversion is possible in any aspect, it must involve keeping the muscle cell from
destroying itself (recall that Type IIx fibers produce an extremely high amount of force)
and cortisol must be blocked before such conversions are possible.
CONCLUSION
This unit introduced you to the structure and function of the skeletal system and the
muscular system which work together as one system. The body works in harmony; every
system and subsystem is vital to growth and development. Tissues of the neuromuscular
system (from the brain to the tendons and ligaments) produce movement. The brain uses
the central and peripheral nervous systems to deliver messages to the body, the muscles
produce force, and the connective tissues (particularly the tendons) regulate that force.
Teach the brain to ask for more, and it will. Allow the rest of the nervous system to deliver
more, and it will. Demand the muscles to produce more, and they will. Finally, ask the
tendons and ligaments to allow more, and they will.
Of course, adaptations require an integrated approach to training, so you will have to
demand more from recovery abilities in order to optimize training. The respiratory system
will have to deliver more oxygen. The digestive system will have to process more nutrients.
The cardiovascular system will have to deliver the oxygen and nutrients as well as take
away waste products. The endocrine system will have to do a better job at regulating
hormonal output in order to allow better utilization of energy and encourage tissue
growth.
Key Terms
actin
action
adenosine triphosphate (ATP)
aerobic
all-or-none reaction
anaerobic
anatomy
appendicular skeleton
axial skeleton
ballistic movements
biochemistry
capillarization
cartilage
collagen
concentric
creatine phosphate (CP)
creatine
eccentric
elastin
feedback loop
hypertrophy
innervation
insertion
involuntary muscle tissues
isometric
isotonic
lactic acid
ligament
muscle spindles
musculoskeletal system
musculotendinous
myofibrils
myofilaments
myosin
origin
pennate
physiology
proprioceptor
sarcoplasm
size principle of fiber recruitment
skeletal system
sliding filament theory
slow-twitch
stretch reflex
synovial fluid
tendon
type I
type IIa
type IIc
type IIx
voluntary muscle tissues
Unit Summary
Movement of the body is contingent on the interaction of the muscular system and the
skeletal system. These two systems are commonly referred to as the musculoskeletal
system and consist of bones, joints, connective tissue, and muscles.
I. The skeletal system consists of bones and connective tissue that help support and
protect the body.
A. The average human adult skeleton has 206 bones; 80 bones in the axial skeleton
and126 bones in the appendicular skeleton.
1. There are five main categories of bones: flat bones, short bones, long bones, sesamoid
bones, and irregular bones.
B. A joint is formed when two bones connect. Joints are classified as either synarthrodial
or diarthrodial.
1. Diarthroidal joints are classified in six categories: arthrodial (gliding), condyloidal
(ellipsiod), enarthrodial (multiaxial ball-and-socket), ginglymus (uniaxial hinge), sellar
(saddle), and trochoidal (pivot) joint.
C. Tendons are extensions of the muscle fibers that connect muscle to bone.
D. Ligaments connect bone to bone.
E. Cartilage is a firm, elastic, flexible, white material. It is found at the ends of ribs,
between vertebrae (discs), on joint surfaces, and in the nose and ears.
II. The muscular system consists of cardiac muscle in the heart, smooth muscle of the
internal organs, and large skeletal muscles that allow the body to move. The average
human body has approximately 600 muscles that work together with the support of the
skeletal system to create motion.
A. The anatomical position is the most widely used reference point for analyzing the body.
1. Anatomical terms include the following: superior (toward the head), inferior (toward the
feet), anterior (toward the front), posterior (toward the back), medial (toward the
midline), lateral (toward the side), proximal (closest to the center of the body), and distal
(furthest from the center of the body).
B. A muscle is a group of motor units with the main purpose of contraction. The points of
muscle attachment are known as the insertion and the origin of the muscle.
1. Three distinct types of muscle fiber are found in skeletal muscle: Type I (slow-twitch),
Type IIa (fast-twitch), and Type IIx (fast-twitch) fibers. In addition, it has been theorized
that a Type IIc fiber exists due to satellite cell fiber fusion.
2. The all-or-none theory states that a unit is either completely relaxed or fully contracted.
3. According to the size principle, motor units are recruited in order according to their
recruitment thresholds and firing rates.
4. Skeletal muscle contraction occurs when the brain sends out an electrical signal that
travels through the spinal cord, to the spinal nerves, to the motor neurons, and sends an
electrical current through the muscle fiber. The electrical signal triggers the release of
calcium, which binds to actin, permitting actin to interact with myosin. ATP provides the
energy that permits the sliding of myosin across the actin. This pulling results in the
shortening of the muscle fiber, an action known as muscle contraction.
C. Resistance exercise results in contractile protein adaptations while cardiovascular
exercise results in mitochondrial and capillary capacity adaptations.
1. Muscular hypertrophy is an increase in the size of muscle fibers and is one contractile
protein adaptation.
2. Muscle hypertrophy is the commonly accepted cause of increase in muscle size.
SECTION TWO
Kinesiology and Biomechanics
Kinesiology of Exercise
Biomechanics of Exercise
Musculoskeletal Deviations
Muscle Mechanics
INTRODUCTION
As an ISSA trainer and fitness educator, you should understand not only the various
techniques of movement, but also how movement impacts posture, body mechanics, and
body musculature. Regardless of student motivation (e.g., improving physique, strength,
endurance, and muscle tone), a basic understanding ofkinesiology and biomechanical
principles plays an important role in establishing fitness training programs for beginners.
kinesiology: The science or study of movement, and the active and passive structures
involved.
Kinesiology is the study of human motion, and it deals primarily with the muscles and
muscle functions. It describes movement, which muscles are involved in the movement,
and how they are involved. Kinesiology explores the muscular involvement in strength
exercises and sport-specific techniques, whilebiomechanics looks at the physical factors
involved in the movement. By applying basic scientific laws, it is possible to come up with
accurate descriptions not only of what should take place in the exercise, but also the role
that each key joint action and muscle plays. Thus by studying the physical characteristics
of the human body and the principles of mechanical physics, you can better guide
workouts. You will also have the basis for selecting and using specific exercises to produce
desired results.
biomechanics: The study of the mechanical aspects of physical movement, such as
torque, drag, and posture, that is used to enhance athletic technique.
Biomechanics is the study of movement more specifically, the movement involved in a
strength exercise or in the execution of a sport skill. It deals mainly with physical factors
such as speed, mass, acceleration, levers, and force, and with the physical functions of the
movement. So, you can think of biomechanics as the science of movement based on
principles derived from physics and anatomy. It explains the why of a movement and how
the movement can be improved through science-based modifications.
Kinesiology tells you exactly which muscles are involved in the particular actions that take
place in an exercise, and biomechanics shows you the way to do exercises most effectively.
Thus, a basic understanding of kinesiology and biomechanics helps you to determine what
exercises a person should do, how the workouts should be conducted, how effective
exercise execution is, and whether the exercises are safe.
UNIT 4
KINESIOLOGY OF EXERCISE
Frederick Hatfield, PhD, MSS & Michael Yessis, PhD
TOPICS COVERED IN THIS UNIT
Kinesiology
Types of Muscle Contractions
Roles of Muscles
Types of Movements
Unit Outline
I. Kinesiology
A. Types of Muscle Contractions
1. Concentric Contraction
2. Eccentric Contraction
3. Isometric Contraction
B. Roles of Muscles
1. Prime Mover (Agonist)
2. Assistant Mover
3. Antagonist
4. Stabilizer
5. Synergy
C. Types of Movements
1. Sustained Force Movement
2. Dynamic Balance Movements
3. Ballistic Movement
4. Guided Movement
5. Planes of Motion
6. Fundamental Movements of Major Body Segments
Learning Objectives
After completing this unit, you will be able to do the following:



Define kinesiology and understand the role it plays in creating effective fitness training
programs.
Understand how the body moves in space and is able to perform complex movements.
Distinguish between different types of muscle contractions.


Know the various types of muscles and their roles in producing movement.
Communicate with clients and fellow health professionals using kinesiology terms.
KINESIOLOGY
Proper exercise selection plays an important role in the overall process of program
development. However, before going into a detailed analysis of exercises and the muscles
involved, you should have a good understanding of how muscles function. It is important
to have a solid comprehension of the various types of muscular contractions, as well as the
different dynamic and static regimes in which the muscles must operate during execution
of strength and explosive exercises. This basic understanding will enable you to effectively
evaluate exercises and exercise execution.
TYPES OF MUSCLE CONTRACTIONS
Muscles perform three types of contractions: concentric, eccentric, and isometric. These
three types are defined next and depicted in Figure 4.1. When executing a strength
exercise, all three of the muscle contractions are involved. As you perform a movement,
the main muscles undergo a concentric contraction while the opposite muscles
undergo an eccentric contraction. The adjacent parts of the body that are not in use are
stabilized via the isometric contraction. Thus, all three operate simultaneously, each
with a very important purpose.
concentric contraction: A type of muscle activation that increases tension on a muscle
as it shortens.
eccentric contraction: A type of muscle activation that increases tension on a muscle as
it lengthens.
isometric contraction: A muscle activation in which the muscle fires but there is no
movement at the joint and no change in length of the muscle.
stabilization: The act of being stable or balanced.
Figure 4.1 Types of muscular contractions
Concentric Contraction
In a concentric contraction, the muscles shorten to produce movement. It is sometimes
known as overcoming strength. In other words, when the muscle contracts, it overcomes
the resistance and the cause of the resistance is set into motion. An example is the biceps
curl. When you contract the biceps and other elbow flexor muscles, you get movement of
the forearm, which raises the weight held in the hand. Concentric strength is usually
measured by the maximum amount of weight that can be overcome in one repetition (also
called one-repetition maximum, or 1RM).
Eccentric Contraction
In an eccentric contraction (often known as a yielding contraction), the muscle lengthens
(stretches) as it contracts. The more the muscle lengthens or the faster it is stretched, the
greater the tension that is developed. The eccentric contraction plays a very important role
in controlling and stopping movement and in preparing the muscles for an explosive type
contraction. For example, in the biceps curl exercise, when you return to the initial
position, the same muscles are involved and they remain under contraction as they
lengthen when you lower the weight. Because gravity is the force involved in lowering the
weight, the eccentric contraction counteracts the pull of gravity to guide the movement.
The intensity of the contraction depends on the resistance being handled. In a ballistic
movement, as the muscle lengthens, it increases in the intensity of its contraction. When it
is strong enough, it stops the movement. The eccentric contraction can generate up to 50
percent greater tension than the concentric. This is why the eccentric contraction is so
powerful not only in controlling and stopping movement, but also in generating sufficient
tension in the muscles in order for them to contract explosively.
Isometric Contraction
In an isometric contraction, the muscle exhibits strength but the limbs do not move. The
muscle develops tension and some shortening of the muscle fibers and tendons occurs, but
the limbs and body do not move. This type of contraction is seen in the stabilization of a
joint or body as when you hold a particular position to execute an exercise. You can
generate approximately 20 percent greater strength in an isometric contraction than you
can in a concentric contraction.
ROLES OF MUSCLES
Prime Mover (Agonist)
A muscle is called a prime mover or agonist when it is the main muscle involved in a
concentric contraction. Thus in the biceps curl, the biceps brachialis and brachioradialis
are agonists for elbow flexion. Also, many muscles are prime movers in more than one
action. For example, the biceps is also the prime mover in forearm supination.
prime mover (agonist): Denoting a muscle in a state of contraction, with reference to
its opposing muscle, or antagonist.
Assistant Mover
An assistant mover usually plays a secondary role to the prime mover muscles involved.
However, secondary muscles sometimes play a main role in certain ranges of motion or
certain exercises. An example is the pronator teres in elbow flexion. It is a prime mover in
pronation and an assistant in elbow flexion. Usually secondary or assistant muscles are not
as powerful in the movement as the main agonists (prime movers).
assistant mover: Muscle that plays a secondary role to the prime mover involved.
Antagonist
An antagonist muscle has an action directly opposite to that of the agonist. When an
agonist undergoes a concentric contraction, an antagonist undergoes an eccentric
contraction to guide the movement and to stabilize the joint. As the movement goes
through the full range of motion (ROM), the antagonist muscle develops greater tension
and stops the movement before it goes beyond the normal ROM.
antagonist: Something opposing or resisting the action of another.
Keep in mind that the role of antagonist and agonist can change depending on the action
thats taking place. For example, in the biceps curl illustrated in Figure 4-2 the biceps is a
prime mover while the triceps is an antagonist. When the triceps is involved in elbow
extension, however, it becomes a prime mover and the biceps becomes its antagonist.
Figure 4.2 Muscle roles: agonist and antagonist
During a muscular contraction, especially when the weights are very heavy, both the
agonist and antagonist undergo contraction (known as co-contraction). This
simultaneous contraction is needed to stabilize (hold in place) the joint while the action
occurs. When the resistance is very light, the agonist and antagonist are not strongly
contracted. The antagonist undergoes a strong eccentric contraction mainly to slow down
and stop movement injury from occurring. When the weights are very heavy and both
agonist and antagonist are under contraction, the antagonist contracts eccentrically,
lengthening in order to make the movement possible.
co-contraction: When both the agonist and antagonist undergo contraction.
Stabilizer
Usually a stabilizer muscle holds a body part in place. It anchors the bone so that the
prime mover has a firm base against which to contract (i.e., for the muscle to pull against).
In order to create precise movements, stabilization of the limb or body part is important in
all movements.
stabilizer: Muscle that steadies or holds a body part in place.
The stabilizer muscle usually undergoes an isometric contraction to hold the bone in place.
At times, there may be slight movement of the body part, but it is still considered
stabilization. For example, in the knee extension exercise with rubber tubing (in which you
hold the thigh at a 45-degree angle and then extend the leg), there may be some natural
movement of the thigh. However, the thigh is still considered as stabilized by the muscles
around the hip joint.
When doing an overhead press, the quadriceps and especially the erector spinae of the
lower back contract to hold the trunk erect as you raise the weights overhead. If these
muscles did not contract, you would have a loose spine that was very susceptible to injury.
You would also lack a firm base against which the muscles could contract. Breath holding
at this time also contributes greatly to stabilizing the trunk. Thus the muscles and
breathing play an important role in stabilization when doing strength exercises, especially
when the weights are heavy.
Because the isometric contraction is used in stabilization, the muscles involved can
become fairly well developed. However, you should not ignore other exercises and exercise
regimes to strengthen the muscles involved. Keep in mind that the isometric contraction is
not as effective as the concentric contraction in developing strength, mass, or definition.
Synergy
Because this term has been used in many different ways, its meaning has become
somewhat diffused. Most often it is used in two ways. First is helping synergy, in which
two muscles contract simultaneously to produce one movement while their other actions
cancel each other out. For example, in the sit-up exercise, when the internal and external
oblique muscles contract, they have a tendency to not only perform spinal flexion but to
rotate the shoulders. In order to prevent the rotation, the internal and external oblique
muscles cancel out their rotational action and the resultant force is used for spinal flexion.
helping synergy: When two muscles contract together to create one movement.
Second is true synergy, in which a different muscle contracts to stop the secondary
action of another muscle. For example, the biceps brachii is both a supinator of the
forearm and a flexor of the elbow joint. Thus, in elbow flexion, the pronator quadratus
comes into play to cancel the supinating tendency of the biceps so that only flexion occurs.
The pronator teres also comes into play, but because it is a flexor of the elbow, it acts as a
helping synergist.
true synergy: When a muscle contracts to stop the secondary action of another muscle.
Synergy can also be used synonymously with the term neutralizer. In other words, a
muscle acts as a neutralizer when it contracts to counteract or neutralize an undesirable
action of another muscle during its contraction.
neutralizer: When a muscle contracts to counteract an undesirable action of another
muscle.
TYPES OF MOVEMENTS
A muscle can contract with different amounts of force and in different ways in order to
produce different types of movement. These types of movements, as well as the planes and
directions in which they move, are described next.
Sustained Force Movement
Sustained force movement is movement in which continuous muscle contractions occur in
order to keep moving a weight. In other words, its the prime muscles involved throughout
the ROM that apply force. It is usually seen in the slow lifting of a heavy weight and
usually involves co-contraction of the antagonists. Sustained force can apply to holding a
weight with no movement (isometric contraction).
Dynamic Balance Movements
Dynamic balance movements are movements in which constant agonist-antagonist muscle
contractions occur in order to maintain a certain position or posture. For example, if you
stand on one leg, you will not be able to stand perfectly still, because the body constantly
makes slight correctional movements. For example, as you begin to lose balance in one
direction, the antagonists contract to pull you back into position. The pull usually takes
you slightly beyond the beginning position, at which time the muscles on the opposite side
contract to bring you back in alignment. Thus there are constant low-level contractions to
keep you in a posture or in balance.
Ballistic Movement
Ballistic movement is movement in which inertial movement exists after an explosive or
quick, maximum-force contraction. Usually there is pre-tensing of the muscle in the
eccentric contraction so that the muscle can contract concentrically with maximum speed
and quickness. The weight is put into acceleration and continues movement on the
momentum generated. No additional force has to be applied to keep the limb or object in
motion. To stop the movement, there is deceleration due to gravity and/or to the eccentric
contraction of the antagonist muscles. The tension the antagonists develop as the ROM
increases becomes strong enough to stop the moving limb. If the limb does not stop, the
weight must be released before you can go into a follow-through phase to dissipate the
forces and come to a complete stop.
Guided Movement
Guided movement is movement that occurs when both the agonist and the antagonist
contract to control the movement. Guided movement is seen most often in fine skills such
as when you are writing or when you must move a limb through a specific movement
pattern. What is very important here is the eccentric contraction of the antagonist muscles
because they are responsible for most of the guiding work. The prime movers are
responsible for putting and keeping the limb in motion.
Figure 4.3 Planes of motion
Planes of Motion
Human movements are commonly described in terms of the planes that they occupy. A
plane is a flat surface. The human body has three imaginary planes that pass through it;
each plane is perpendicular to each of the other two.
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
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The sagittal (anteroposterior) plane is a vertical plane passing through the body from
front to back, dividing the body into left and right portions.
The frontal (coronal) plane is a vertical plane passing through the body from left to
right, dividing it into front and back portions.
The transverse (horizontal) plane passes through the body in a line parallel to the
ground, dividing the body into upper and lower portions.
sagittal (anteroposterior) plane: Separates the body into right and left sections.
frontal (coronal) plane: Separates the body into anterior (front) and posterior (back)
parts.
transverse (horizontal) plane: Separates the body into superior (top) and inferior
(bottom) sections.
Two examples that may help describe the orientation of movement are given here. The
first is a typical biceps curl. Concentric contraction of the biceps occurs in the sagittal
plane. Second, abduction of the arm, as in a lateral dumbbell raise, occurs in the frontal
plane. The standardized reference position from which movements of the body are
described is the anatomical position, in which the body is facing forward, arms at the sides
and palms forward.
Now that you have a basic understanding of muscles and muscle functions as they relate to
human motion, you will now enter the study of movement, more specifically, the
movement involved in strength exercises and other exercises.
Table 4.1
Fundamental Anatomical Movements
PLANE OF
MOTION
ACTION
DEFINITION
Frontal
Abduction
Movement away from the midline of the body
Adduction
Movement toward the midline of the body
Elevation
Moving to a superior position at the scapula
Depression
Moving to an inferior position at the scapula
Inversion
Lifting the medial border of the foot (insole)
Eversion
Lifting the lateral border of the foot
Sagittal
Transverse
Multiplanar
Flexion
Decreasing the angle between two bones
Extension
Increasing the angle between two bones
Dorsiflexion
Moving the top of the foot toward the shin at the
ankle joint
Plantarflexion
Moving the top of the foot away from the shin at
the ankle
Rotation
Internal or external turning about the vertical axis
of a bone
Pronation
Rotating the hand and wrist medially from the
elbow
Supination
Rotating the hand and wrist laterally from the
elbow
Horizontal
adduction
From a 90° abduction arm position, the humerus
is flexed toward the midline of the body in the
transverse plane
Horizontal
abduction
From a 90° adduction arm position, the humerus
is extended away from the midline of the body in
the transverse plane
Circumduction
Combination of flexion, abduction, extension, and
adduction in a sequence
Fundamental Movements of Major Body Segments
Several movements are possible in many joints. Six primary movements occur at the joints
between the body segments: flexion, extension, abduction, adduction, rotation, and
circumduction (defined next). As a trainer, you must become familiar with the terminology
of these fundamental anatomical movements.

Flexion is a decrease in the angle between two body segments. Flexion occurs at the
shoulder, elbow, hip, and knee joints. For example, on the arm curl machine, flexion takes
place at the elbow. Special flexions occur at the trunk (lateral flexion or bending sideways);
the wrist (ulnar flexion or bending toward the pinky side of the hand, and radial flexion or






bending toward the thumb side); and the ankle (dorsiflexion, or toes up,
and plantarflexion, or toes down).
Extension is an increase in the angle between two body segments, or the return from
flexion. For example, extension occurs at the knee on the leg extension
machine. Hyperextension is the increase in the angle beyond the anatomical point of
normal joint movement. Hyperextension occurs during the back swing in bowling
(shoulder joint), in a neck bridge in wrestling (neck), and on the standing hip machine
when the leg is lifted behind the body (hip joint).
Abduction is the movement of a body segment away from the midline. Examples
include a dumbbell lateral raise, spreading of the fingers or toes, or the legs moving apart
on a hip abductor machine.
Adduction is the movement of a body segment toward the midline, or the return from
abduction, as on the hip adductor machine when the legs come together.
Rotation is the circular movement of a body segment about a long axis. Inward rotation
occurs when a body segment moves towards the midline (the upper arm when throwing a
screwball), while outward rotation occurs when a body segment moves away from the
midline (the upper arm in a backhand tennis stroke). Right and left rotation defines the
directional rotation of the head or trunk.
Special rotations occur at the forearms and feet. Pronation is the rotation of the forearm
to the palms-down position (as in a basketball dribble or on the seated chest press
machine). Supination is the rotation of the forearm segment to the palms-up position (as
in doing a standard curl on the arm curl machine). Eversion (also called pronation of the
foot) is the outward tilting of the sole of the foot, while inversion (also called supination
of the foot) is the inward tilting of the sole of the foot—a common cause of ankle injuries.
Circumduction is the sequential combination of movements outlining a geometric cone.
Examples include circles of the trunk, shoulder, hip, ankle, and thumb.
flexion: A decrease in the angle between two body segments.
dorsiflexion: Turning upward of the foot or toes or of the hand or fingers.
plantarflexion: Extension of the ankle, pointing of the foot and toes.
extension: An increase in the angle between two body segments, or the return from
flexion.
hyperextension: Extension of a limb or part beyond the normal limit.
abduction: Movement of a body part away from the midline.
midline: An imaginary longitudinal line that travels down the center of the body.
adduction: Movement of a body part toward the midline.
rotation: Circular movement of a body segment about a long axis.
pronation: Assuming a facedown position. Of the hand, turning the palm backward or
downward. Of the foot, lowering the inner (medial) side of the foot so as to flatten the
arch. The opposite of supination.
supination: Assuming a horizontal position facing upward. In the case of the hand, it
also means turning the palm to face forward. The opposite of pronation.
eversion: Turning outward, as of the sole of the foot.
inversion: Turning inward, as of the sole of the foot.
circumduction: Movement of a part, e.g., an extremity, in a circular direction.
Table 4.1 on the previous page includes these fundamental movements and defines more
detailed movements as well. Figures 4.4 through 4.6 illustrate these movements according
to their planes of motion.
Figure 4.4 Movements occurring in the frontal plane
Figure 4.5 Movements occurring in the sagittal plane
Figure 4.6 Movements occurring in the transverse plane
Key Terms
abduction
adduction
antagonist
assistant mover
biomechanics
circumduction
co-contraction
concentric contraction
dorsiflexion
eccentric contraction
eversion
extension
flexion
frontal (coronal) plane
helping synergy
hyperextension inversion
isometric contraction
kinesiology
midline
neutralizer
plantarflexion
prime mover (agonist)
pronation
rotation
sagittal (anteroposterior) plane
stabilization
stabilizer
supination
transverse (horizontal) plane
true synergy
Unit Summary
Kinesiology is the study of human motion, dealing mainly with the muscles and muscle
functions.
I. There are three main types of muscle contractions: concentric, eccentric, and isometric.
A. In a concentric contraction, the muscle shortens to produce movement.
B. In an eccentric contraction, the muscle lengthens (stretches) as it contracts.
C. In an isometric contraction, the muscle exhibits strength, but the limbs do not move.
II. As you perform a movement, the agonist muscles undergo a concentric contraction
while the antagonist muscles undergo an eccentric contraction. The adjacent parts
stabilize the body via the isometric contraction. Thus, all three operate simultaneously,
each muscle with a specific muscle role.
A. A prime mover (agonist muscle) is the main muscle involved in a concentric
contraction, such as the biceps during biceps curl.
B. An assistant mover usually plays a secondary role to the prime mover muscles involved.
For example, the pronator teres is a prime mover in pronation and an assistant in elbow
flexion.
C. An antagonist muscle has an action directly opposite that of the agonist. For example,
the triceps is antagonist to the biceps.
D. A stabilizer muscle is a muscle that holds a body part in place.
E. Muscles can exhibit helping synergy or true synergy.
1. Helping synergy occurs when two muscles contract simultaneously to produce one
movement while their other actions cancel each other out, such as internal and external
obliques during a crunch.
2. True synergy occurs when a different muscle contracts to stop the secondary action of
another muscle. For example, the pronator quadratus cancels the supinating tendency of
the biceps so that only flexion occurs.
III. A muscle can contract with different amounts of force and in different ways to produce
different types of movement.
A. A sustained movement is one in which there is continuous muscle contraction to keep
moving a weight.
B. Dynamic balance movements are movements in which there are constant agonistantagonist muscle contractions to maintain a certain position or posture.
C. Guided movement is movement that occurs when both the agonist and the antagonist
contract to control the movement.
D. A ballistic movement is one in which there is inertial movement after an explosive or
quick, maximum force contraction.
E. Six primary movements occur at the joints between body segments: flexion, extension,
abduction, adduction, rotation, and circumduction.
1. Flexion is a decrease in the angle between two body segments.
2. Extension is an increase in the angle between two body segments.
3. Abduction is movement away from the midline of the body.
4. Adduction is movement toward the midline of the body.
5. Rotation is the circular movement of a body segment around a long axis. Special
rotations occurring at the forearms and feet include pronation, supination, inversion, and
eversion.
6. Circumduction is the sequential combination of movements outlining a geometric cone.
F. Human movements are commonly described in terms of the planes they occupy. There
are three imaginary planes that pass through the human body: the sagittal, frontal, and
transverse plane.
UNIT 5
BIOMECHANICS OF EXERCISE
TOPICS COVERED IN THIS UNIT
Biomechanics and Personal Training
Key Concepts of Biomechanics
Stability
Force
Angle of Muscle Pull
Work
Power
Newton’s Laws of Motion
Levers
Wheel and Axle
Pulley Systems
Torque
Pushing
Pulling
Gravity
Kinesthesis
Vision
Conclusion
Unit Outline
I. Biomechanics and Personal Training
II. Key Concepts of Biomechanics
A. Stability
B. Force
C. Angle of Muscle Pull
D. Work
E. Power
F. Newton’s Laws of Motion
1. Newton’s First Law: Inertia
2. Newton’s Second Law: F = MA
3. Newton’s Third Law: Action–Reaction
G. Levers
1. First-class Lever
2. Second-class Lever
3. Third-class Lever
H. Wheel and Axle
I. Pulley Systems
J. Torque
K. Pushing
L. Pulling
M. Gravity
1. Center of Gravity
2. Line of Gravity
N. Kinesthesis
O. Vision
III. Conclusion
Learning Objectives
After completing this unit, you will be able to do the following:


Understand what occurs during execution of strength and other exercises.
Define the mechanical and physical factors involved in exercise and movement.
BIOMECHANICS AND PERSONAL TRAINING
Now that you understand the basics of kinesiology, you can move on to biomechanics,
which is the physical study of movement. Knowledge of joints, muscles, and their possible
actions leads to a better understanding of what occurs during the execution of strength
and other exercises. As a trainer, you must understand the mechanical and physical factors
involved in exercise and movement. These factors determine how effectively and safely an
exercise is executed. When you combine your knowledge of anatomy with kinesiology and
biomechanics, you have powerful tools for creating personalized programs for your clients
and executing them in effective, efficient ways.
biomechanics: The study of movement.
KEY CONCEPTS OF BIOMECHANICS
Your knowledge of biomechanics will help you to create safe, effective, efficient personal
training programs for your clients. The following sections provide brief descriptions of key
biomechanical concepts. Examples of specific exercises are used where applicable but will
be discussed in detail in Unit 8.
STABILITY
Stability is the ability to maintain a balanced state. In order to ensure safety during
exercise execution, stability in the body is necessary. Stability helps produce the desired
results when using free weights; you must stabilize yourself in order to isolate the desired
movement and perform it correctly. With machine weights, when you assume the
necessary position, there is little need to balance your body as you execute the exercise; the
machine stabilizes itself along the movement path so that its user can perform the exercise
correctly.
stability: The ability to maintain a balanced state.
For example, when doing an overhead press, the muscles of the legs and trunk must
contract in order to hold the body in place. The trunk must be rigid in order to provide a
stable base for effective contraction of the shoulder muscles. If not, any change in the
balance of the weights overhead may lead to a loss of balance, which in turn could cause
injury, especially if you lose control of the weights.
The basic principles of stability are simple. One such principle is that the larger the base of
support, the greater the body’s stability. This is why you should most often assume a
position with the feet at approximately shoulder width or wider. Standing with your feet
together results in a narrow base of support, which does not provide the foundation
needed for stability when doing heavy lifts, especially overhead lifts.
Another basic principle of stability is that the lower the body is, the more stable it
becomes. Bending the knees helps to lower the body’s center of gravity (where the
bodyweight is concentrated). For example, in order to prevent lower-body movement and
keep the spine vertical during shoulder (upper-body) twisting, it is important to bend the
knees to stabilize the lower body and hips. This position keeps the spine from falling out of
alignment and limiting the movement to the shoulders. The bent-knee position also helps
to prevent knee injuries.
Foot placement also plays an important role. If the feet are parallel and shoulder-width
apart (A), the weight should be close to you or overhead. This is the preferred stance in
most exercises because you have good stability in a left to right direction. In a stride
position (B), you can better balance the weight in a forward–backward direction.
When lying on a bench, always place the feet on the floor (C) in order to increase sideward
stability. Keeping the feet on the bench creates an unstable position, especially when using
heavy weights or a barbell. It becomes even more important to keep the feet on the floor
when doing explosive or throwing actions.
FORCE
Force is the interaction that creates work, action, or physical change. Muscular force is
exhibited in a push or pull type motion. Only the muscles (or, more accurately, muscle
strength) can create the force needed in order to put an object into motion. When moving
a weight in a strength exercise, you must take four components of force into consideration:
magnitude, direction, point of application, and line of action.
force: The interaction that creates work, action, or physical change.
Magnitude refers to how much force is applied to the dumbbells, barbells, or machine
handles. For example, if you wish to lift a barbell weighing 100 pounds, you must apply
more than 100 pounds of force to lift it. Keep in mind that additional force is needed in
order to overcome the weight of the limbs and body involved and to overcome resting
inertia.
magnitude: How much force is applied to the dumbbells, barbells, or machine handles.
Direction refers to the way in which the force is applied. For example, is it applied
horizontally, vertically, or a combination of both? This information is especially important
in sports such as running, swimming, and in the throwing events.
direction: The way in which the force is applied.
Point of application refers to where the force is applied on the body or implement being
used. It plays a role in many exercises including the overhead press and the squat. For
example, if you hold a barbell in the middle of the bar with your hands close to one
another, the force applied is close to the center of mass of the bar and the exercise
becomes more effective. But in this situation, greater balance is also needed, especially if
the barbell is long (such as an Olympic bar). In this case, you must assume a wider grip, in
which you apply force at two points to raise one barbell. This position loses efficiency but
enhances safety and enables you to do the exercise. In sports, the point of application of
force is where the hand or fingers are in contact with a ball when shooting (basketball) or
throwing (baseball). In hitting, it is where the ball and hitting implement make contact; for
example, a golf ball on the club head, a baseball on a bat, or a tennis ball on a racquet.
point of application: Where the force is applied on the body or implement being used.
Line of action (also line of force) refers to an imaginary straight line drawn from the
point of application of force through the direction of force. The more directly the force is
applied in exactly the same direction as the intended movement, the greater the amount of
force that goes in this direction. It is important to understand that you can push in one
direction to get motion in another direction, usually a side component. For example, if you
have a very wide stance in the squat, as in the sumo style, you have less distance to rise up
when doing the squat. However, the force generated by each leg does not go straight
upward; it is at an angle to the body. As a result, only a portion of the total force raises you.
To raise all of the applied forces that go through the body’s center of gravity, you must
keep the feet under the hips. In sports, the legs must drive the hips upward or forward or a
combination of both in various jumping and running actions. Thus, it is important that the
feet remain directly under the hips when the force is applied in the intended direction.
line of action (line of force): An imaginary straight line drawn from the point of
application of force through the direction of force.
ANGLE OF MUSCLE PULL
When you do a strength exercise, the strength exhibited at different points in the range of
motion varies because of the angle at which the muscle pulls. For example, if you do a
biceps curl beginning with fully extended arms, it is more difficult to generate sufficient
force in order to start moving the weight than when you start with the arms bent. When
your arm is straight, the biceps muscle inserts at an angle of approximately 10 degrees on
the radius bone of the forearm. When the muscle shortens (i.e., when you begin the curl),
most of the muscle’s force goes into the joint
angle of pull: The angle at which a muscle pulls relative to the long axis of the bone on
which it pulls.
in order to stabilize the elbow rather than to raise the forearm with the weight. When the
angle of insertion approaches 90 degrees, all the force of the muscle is used in raising the
weight (all the strength generated is used to rotate the forearm). So, you are much
stronger when there is approximately a 90-degree angle in the elbows than when the arms
are extended. This is known as having a mechanical advantage, which means that you can
do more work at this angle of muscle pull.
If you use a weight that is the heaviest you can overcome in the early range of motion, it
may appear light when you approach the 90-degree angle in the elbow. To overload the
muscle in this range you must use more weight or go through a shorter ROM resulting in
your arms not fully straightening in the bottom position. Doing only this over a long
period of time, however, results in loss of flexibility.
The body is best suited for speed, not force. Thus, even though you are weak at the
beginning of a straight-arm elbow flexion movement, you possess the ability to develop
great speed in the hand (if the resistance is not too great). Very little shortening of the
muscles produces a large movement of the hand. This is known as having a physiological
advantage, which is very important in speed and quick movements.
WORK
In physics, work refers to what happens when a force is applied to an object. The actual
amount of work that you do is measured by the formula W = F × D, where W= work, F=
force, and D= distance or displacement of the object being moved. The greater the force
and the greater the distance over which the force is being applied (the weight is moved),
the more work is done. When you hold a weight in the hands with an isometric
contraction—even though the muscles are generating great tension and you may use a lot
of energy to hold the position, you are not doing any work because you are not moving the
weight any distance. For work to be done, there must be movement. If not, you are only
expending energy, which is not work. Energy is more physiological, while work is more
mechanical.
work: Force times distance. Measured in foot-pounds and similar units. Example: Lifting
a 200-pound barbell 8 feet and lifting a 400-pound barbell 4 feet each require 1,600 footpounds of work.
POWER
The term power is often misused in fitness and sports literature. Power is often equated
with the amount of force one generates, but this is only partially correct. In physics and in
most sports, power is defined as the work done in a unit of time. To calculate it, you must
first consider the time involved in executing the movement. For example, if you do a squat
with a 300-pound barbell and you move the barbell three feet from the bottom position to
the top position, you will have done 900 foot-pounds of work (W = 300 lb × 3 ft = 900
fi•lb). In reality, you actually lifted more. But for simplicity, your body weight and external
factors are not taken into consideration.
power: The work done in a unit of time.
To calculate power, you can use the same example, but consider the amount of time it took
to lift the weight 3 feet. For simplicity, assume it took 3 seconds. Therefore, 900 footpounds of work divided by 3 seconds equals 300 foot-pounds of work per second. If you
executed the squat in approximately 2 seconds, then the amount of power generated
would be 450 foot-pounds per second. Thus you can see how the amount of power
generated depends very much on the amount of time it takes to accomplish the work. The
faster the work is done, the greater the amount of power; the slower the work is done, the
lesser the amount of power.
Much confusion has arisen in this area because of powerlifting. In this sport, maximal
weights are lifted slowly, so it should be considered a pure strength sport (rather than a
power sport). The amount of power is not great in comparison to that of a weightlifter,
who lifts maximal weights as quickly as possible. The weightlifter exhibits much greater
power than the powerlifter, but the powerlifter exhibits greater strength than the
weightlifter.
NEWTON’S LAWS OF MOTION
Isaac Newton’s three laws of motion contribute to the key principles of biomechanics by
describing inertia; the relationship between force, mass, and acceleration; and the
relationship between equal and opposing forces. Understanding these three laws and how
they apply to training will help you create thoughtful training sessions.
Newton’s First Law: Inertia
Newton’s first law states that an object at rest tends to stay at rest, and an
object in motion tends to stay in motion; this is the essence ofinertia. There are
two types of inertia: resting inertia and moving inertia. Resting inertia means
that when an object is at rest, it will stay at rest unless acted upon by some
outside force. For example, a loaded barbell or dumbbell lying on the ground has resting
inertia. In order to lift it, you must apply a force greater than the weight of the implement
itself.
inertia: The tendency for an object to remain in its current state (in motion or at rest).
resting inertia: An object is at rest, it will stay at rest unless acted upon by some outside
force
Moving inertia means that when an object is in motion, it will remain in motion
unless acted upon by some outside force. Thus, once you put a barbell or dumbbell
into motion, it will continue on its own accord without additional application of force to
keep it moving. This can easily be seen with lighter weights. For example, when doing
lateral arm raises with straight arms and light weights, you will experience the weights
“flying” upward without your effort if you apply a vigorous thrust in the bottom position.
moving inertia: An object that is in motion will stay in motion unless acted upon by
some outside force.
When you use heavy weights in a strength exercise, the movement is slow so that you must
apply force through the entire range of motion (ROM) in order to keep the weights in
motion. In this case, although the heavy weights are moving, they will quickly stop because
of the constant force of gravity. Gravity pulls down and thus creates the slow speed.
However, if the weight moves too fast (like when you “throw” a heavy weight, such as a
medicine ball), it may require great force to stop it at the end of the ROM. If your muscles
are not capable of generating this stopping force, injuries can occur if you do not release
the weight. The role of the eccentric contraction is especially important here.
range of motion (ROM): The movement of a joint from full flexion to full extension.
Figure 5.1 Newton’s first law of motion
The further away the mass of the object is during weightlifting, the greater the inertia,
especially on the return. This means that when the weight is moving, it is more difficult to
control regardless of whether it is moving up or down, although it is especially difficult on
the down return when gravity pulls. Because of this fact, you should always position
yourself as close as possible to the weight you are lifting. The closer the weight, the easier
it becomes to control; it has less lateral rotational inertia. The further away the mass, as in
straight-arm front or lateral arm raises, the more difficult it is to move the weights with
control.
Note also that with straight arms, you can use a lighter weight and it will feel the same as a
heavy weight held at half the distance. Because of this fact, most bodybuilders bend their
elbows to bring the weights closer to their bodies. A bent-elbow position also allows them
to use more weight. However, it is important to understand that when you bend the elbow,
you may be putting the arm in a different position, which will change the muscular
involvement. In the front-arm raise when you bend the arms, the elbows may turn out
approximately 45 degrees. You will therefore be doing a combination of front and lateral
arm-raise exercises.
The use of heavy weights is not always best for precise strength development. By using a
long lever arm to create greater rotational inertia, you can create great resistance with
lighter weights. Also very important to consider is that the stress on the spine is
considerably less when lighter weights are used. This consideration is especially important
for beginners.
Newton’s Second Law: F = MA
Newton’s second law of motion deals with force and its relationship
to mass and acceleration. In essence, in order to create a force, you must place a
mass into motion with acceleration and a change in velocity. Note that mass
multiplied by velocity is known as momentum. Thus in the previous weightlifting
example, when a weight (mass) is moving (has velocity), it has momentum.
mass: A body of coherent matter.
acceleration: The rate of change of velocity per unit of time.
velocity: The speed of something in a given direction.
momentum: The quantity of motion of a moving body, measured as a product of its mass
and velocity.
Momentum is seen in many exercise machines that use weight stacks attached to a cable.
When you do the exercise, you must adjust the speed of your movement to how fast the
weights move up and down. If you move the resistance levers at a very fast rate, the weight
stack will continue to move when you stop. Thus, at times, the weight may be going up
when it should be going down, or vice versa. When this happens, the cables may bind or
snap off the pulley. Therefore, to do an exercise quickly, you must use machines that allow
for quick movements, or you must use free weights or rubber tubing (resistance bands).
Figure 5.2 Newton’s second law of motion
A key point to keep in mind while training is that when the muscle generates a force, there
must be acceleration of the weight. In other words, the speed of the object must be
increasing in order to be a true force. When first starting an exercise, you must generate
force. When the weight is stationary and you begin movement, you accelerate the weight.
However, once the weight is in motion, it only has velocity. You are no longer creating
force unless you are changing the speed of the object.
In essence, you must place the weight into acceleration in order to get it moving. Once the
weights are in motion, they have momentum. For some reason, acceleration and
momentum of weight have become unacceptable to many trainers. They consider
acceleration and momentum dangerous—to be avoided at all costs. Rather than avoiding
it, though, you should understand what is taking place and thus prepare the body to
handle the forces that are encountered. Force, acceleration, and momentum can be your
allies rather than your enemies. The key is to learn how to work with them in order to
make the best use of them.
If a force is maximal or if a weight is accelerated at a maximal speed, then you must
release it in a throwing or pushing action because it will be impossible for the muscles of
the body to stop the weight or the limb from continuing its movement. The heavier the
weight or the greater the acceleration of the weight, the more difficult it is to stop it. It is
because of this that most strength exercises are performed at a slow to moderate speed.
Note that even lighter weights can generate a lot of force when they are accelerated, as in
some aerobic routines. A 5-pound weight with extended arms moving rapidly can generate
a tremendous amount of force that must be stopped by the eccentric contraction of the
antagonist muscles. If the muscles are not sufficiently strong to stop the movement, an
injury may occur. In general, you can increase speed of execution in some exercises
(usually at the beginning of the movement) so that momentum will carry the weight
through the remaining range before damage is done to the joints. However, a strong
eccentric contraction of the antagonist muscles is still needed in order to stop the
movement.
In addition to creating force to move a weight against the pull of gravity, it is also
necessary to create a force to counteract gravity when lowering weights. In this case,
gravity is the major force pulling the weight down. The muscles contract eccentrically in
order to create the force needed to control the downward movement of the weight. Keep in
mind that gravity causes a weight to go into motion at increasingly greater rates of speed.
Gravity exhibits an acceleration of approximately 32.2 feet per second squared (32.2
ft/sec2). Thus for every second of downward fall, a weight gains greater speed.
Care must be taken when handling weights, especially heavy weights. If they drop from a
high height, the amount of force upon landing can be extremely high. Even the height of a
few feet can cause a weight to have a force of several times its actual weight. Because of the
acceleration produced by gravity, you must always control the weights on the (negative)
return with the eccentric contraction.
Newton’s Third Law: Action–Reaction
Newton’s third law of motion is also known as the equal and opposite reaction
principle and it applies to weightlifting and bodybuilding exercises. The law states
that objects in contact exert equal and opposite forces on each other. When
doing an exercise such as the push-up, you must push against the floor with your hands.
The floor, in turn, pushes against you and as a result you raise the trunk. This is known as
reactive force. The same concept applies when jumping. When you land on the ground,
you apply a force against the ground; in turn, the ground applies an equal and opposite
force against you to propel you into the air.
Figure 5.3 Newton’s Third Law of Motion
LEVERS
A lever is a rigid bar that turns about an axis of rotation, called a fulcrum. In the body,
bones represent bars, joints represent fulcrums, and muscle contractions represent force.
The lever rotates about the fulcrum as a result of the force being applied to it, causing its
movement against a resistance (e.g., a weight). The amount of resistance can vary from
maximal to minimal. In fact, the bones themselves or the weight of the body segment may
be the only resistance applied. All lever systems have each of these three components in
one of three possible arrangements. The arrangement of these points and the direction in
which the force is being applied will determine the type of lever being used.
lever: Rigid bar that turns about an axis of rotation or a fulcrum.
fulcrum: The point on which a lever rests or is supported and on which it pivots.
Figure 5.4 Lever and fulcrum with effort and resistance applied
First-class Lever
The first-class lever (see Figure 5.5A) is similar to the seesaw, in that it has its fulcrum
between the force and the resistance. When you sit on one end, you apply a downward
resistance on one side, of the fulcrum and an upward force on the other side. If someone
else sits on the opposite side another downward resistance is brought into play. And if the
weights are equal and the distance from the fulcrum is equal, you will be in balance with
no movement occurring. In order to get movement, you will have to make your body
heavier (or lighter) to place it into motion. Nodding the head is an example of a first-class
lever. The head is the resistance, and the contraction of the neck muscles lifts the weight
around the fulcrum (the joints of the neck). First-class levers do not produce a great
amount of force. They do produce a maximum ROM and speed of movement.
first-class lever: Fulcrum in the middle, the effort is applied on one side of the fulcrum
and the resistance on the other.
Second-class Lever
In the second-class lever (see Figure 5.5B), the weight (resistance) is distributed
between the axis of rotation (fulcrum) and the application of force. This type of lever is
most suited for a gain in force. Picture a wheelbarrow: The fulcrum is the wheel, and the
weight is in the bucket located in the middle; the action of your arms pulling upward on
the handles generates the force. The second-class lever is exemplified when you rise up on
your toes. This type of leverage allows you to walk and run, and is effective for overcoming
resistance. One weight-training exercise that utilizes the second-class lever is the push-up.
In this case, the fulcrum is the balls of the feet in contact with the floor, the weight is the
center of gravity of your body mass, and the force is in the arms, pushing you upward.
second-class lever: A lever in which the load lies between the fulcrum and the effort.
Figure 5.5 (A) First-class lever. An example is nodding your head. This lever works like
a teeter-totter. (B) Second-class lever. This lever works like a wheelbarrow. When going
up on your toes, this lever system allows you to lift your body weight with very little
effort. (C) Third-class lever. This lever works like a piston in an engine.
Third-Class Lever
In the third-class lever (see Figure 5.5C), the force is applied between the fulcrum and
the resistance. This is the most common type of lever found in the body. For example, in
the biceps curl, the biceps inserts approximately 1 inch below the elbow joint. The point of
attachment is known as the point of application of force. The elbow is the axis of rotation
(fulcrum), and the resistance is the forearm and weight held in the hand. Thus the distance
from the point of application of force to the fulcrum (called the force arm) is very short
and mechanically inefficient. The key reason for this inefficiency is that the resistance arm
(the distance from the fulcrum to where the weight is located) is quite long. This
configuration places the weight far from the application of force. A short force arm and a
long resistance arm is a
third-class lever: A lever in which the effort is placed between the fulcrum and the load.
most advantageous configuration for speed but not for the production of force. In the case
of speed, a short contraction of the muscle can move the end of the limb (hand) a great
distance, even though little movement occurs at the actual insertion of the muscle on the
bone. This relationship is also advantageous for ROM. The speed advantage of the thirdclass lever system is most important in sports, not when lifting weights. People with short
limbs have an advantage in lifting heavier weights because of their shorter resistance
arms. However, exceptions do exist. For example, in the deadlift, longer arms allow you to
raise the weight a shorter distance.
WHEEL AND AXLE
Wheel and axle–like arrangements in the body are needed for the transmission of force. A
good illustration of this arrangement is shoulder joint medial and lateral rotation. For
example, hold the upper arms in line with the shoulders, elbows bent 90 degrees, and the
forearms vertical and holding a weight or ball in the hands. Lower the forearm downward
behind the head, maintaining the 90-degree angle (or greater) in the elbow in order to
execute lateral rotation with the fulcrum along the long shaft of the humerus.
When you raise the hand in the opposite action, you execute medial rotation in which the
humerus rotates in the opposite direction on its long axis. In this case, a short radius of
rotation of the humerus exists. But with the forearm bent at a 90-degree angle, you
generate considerable speed or force at the end of the forearm (the hand). Many strength
exercises involve some rotation of the arms (or legs). To prevent injury when executing
medial and lateral rotation, you should not execute other actions in the same joint at the
same time.
PULLEY SYSTEMS
Another muscular-structural arrangement is the pulley. Pulleys are very common in
exercise machines—such as in the lat pull-downs—to create a greater mechanical
advantage and to move the limbs freely. In the body, a pulley-type system exists in the
knee joint, more specifically, with the patella. The quadriceps tendon (patellar ligament)
goes over the patella to insert on the tibia bone in the shin. Because of the patellar
protrusion, the quadriceps tendon inserts a greater angle in order to create more of a
straight-line force when the knee is in the bent position. As a result, you can generate
greater force, which goes around the patella to change the direction of pull. Few such
pulley-type arrangements exist in the body.
Most pulley (cable) systems in weight machines create the ability to guide and move the
resistance handles in various directions. Depending on the configuration of the pulley or
pulleys, you can increase or decrease the amount of effective resistance. Some pulley
machines even have an extremely strong negative component. After you do the exercise
and the weight stack is raised, the amount of force involved in lowering the weights can be
extremely high. Thus, care must be taken on different exercise machines. To prevent
injury, examine them before using appreciable weight.
TORQUE
The concept of torque is important in understanding how force is produced in weighttraining exercises. Its definition is simple: It is the magnitude of twist around an axis of
rotation (fulcrum). Thus, torque (twist) is rotary (angular) movement in any plane about
an axis. Torque is seen in almost all movements of the body as, for example, when you do
single-joint actions. In isolated movements, the axis of rotation is fixed so that the bony
lever moves in a circular arc. For example, in knee-joint extension, the foot circumscribes
an arc of a circle because it is moving on an angular pathway. When you twist the
shoulders, they rotate around a stationary vertical axis and make an arc of a circle when
viewed from above.
torque: The magnitude of twist around an axis of rotation (fulcrum).
When torque is produced, the force is applied at some distance away from the axis of
rotation. For example, picture yourself driving a car and turning the steering wheel. The
hand applies a force on the wheel (rim) with the axis in the center of the steering column.
This is known as an off-center force or, more accurately, an eccentric force. But the
rotating (turning) force is called torque. Note that the axis of rotation could also be in
motion. This is sometimes needed for safety.
For example, in the seated leg extension exercise in which the thigh is immobile, the forces
generated in the knee joint are extremely high when the leg straightens. Consequently, this
exercise has been negatively criticized as being potentially dangerous. Exercises with
rubber tubing counter this danger. Assume a standing position and hold the thigh up at
approximately 45 degrees. Then straighten the leg against the resistance of rubber tubing.
In this action, the thigh moves slightly as the leg is extended and the axis therefore moves.
Thus the thigh is a “safety valve,” helping to decrease the negative forces and making the
movement more natural, especially for sports such as running.
PUSHING
In some compound (multi joint) exercises, rather than solely using a rotary component to
move the weight, you use a push pattern in which the hands or feet move in a straight line.
This pushing action is seen in exercises such as the leg press, overhead press, dips, and
triceps pushdown. To move the extremity in a straight line, you must involve more than
one joint action. For example, in the leg press, there are simultaneous rotary actions at the
knee (extension) and hip (extension) joints to move the feet in a straight line. In the
overhead press, the shoulder joints undergo flexion (elbows in front) or abduction (elbows
out to the side) as the elbow joints undergo extension. The hands then move in a straight
line upward.
PULLING
Pulling is the opposite of pushing. The hands or feet move in a straight line while two or
more joints are in rotary action. For example, in the seated row, your body is stable and
your hands move in a straight line as you pull them in toward the body. Extension in the
shoulder joint along with flexion in the elbow joint occurs simultaneously in order to allow
the hands to move in a straight line. The same occurs when doing a chin-up or pull-up. In
this case, the body moves in a straight line upward while the hands remain in place, and
there is flexion in the elbow joint together with extension or adduction in the shoulder
joint.
GRAVITY
Gravity is the downward pulling force that creates resistance. For maximum resistance
when using free weights, body position should be adjusted so that the weight that you are
handling is moving as much as possible against the pull of gravity. For example, in the
triceps kickback, only when your arm is almost fully extended does the triceps work fully
against gravity in the upward phase of movement. When the forearm is vertical, there is
very little resistance to overcome. The resistance increases as the arm straightens because
you are now working more against the pull of gravity.
gravity: The downward pulling force that creates resistance.
To make the triceps kickback most effective, the body should be horizontal so that the
ending ROM is against gravity. Since the triceps is also involved in shoulder extension, you
should then raise the straight arm upward above the level of the back. This makes the
movement much more difficult since you now have a long lever when raising the dumbbell
against the pull of gravity. This action goes completely against gravity and you will find
that is more difficult than all the preceding movements.
Figure 5.6 Center and line of gravity
Center of Gravity
Center of gravity is referred to as the point in the body around which your weight is
equally distributed. It is considered to be the point where all your weight is concentrated
(balanced). This point is usually located in the hips, but it can also fall outside the body, as
for example, when the body is rotating in space in a pike position.
center of gravity: The point in the body around which your weight is equally
distributed.
Line of Gravity
When you drop a vertical line straight down from the center of gravity, it is known as
the line of gravity. It should fall within your base of support (formed by an outline
around your feet (in order for you to be in balance. If it falls outside the base of support,
you will be in motion: The motion of falling. When doing strength exercises, it is critical
that the line of gravity falls within your base of support in order for you to remain in
balance.
line of gravity: A vertical line straight down from the center of gravity.
KINESTHESIS
Kinesthesis is the ability to perceive your position and movement of the body or body
limbs in space. Kinesthesis relies on the use of various receptors in the joints, muscles, and
tendons. For example, the muscle spindle, which lies in parallel with the muscle fibers, is
activated when the muscle is stretched during an eccentric contraction. (This action is
known as the stretch reflex.)
kinesthesis: The ability to perceive your position and movement of the body or body
limbs in space.
The Golgi tendon organs are other receptors located at the junction of the tendon and the
muscle. They respond to the amount of stretch taking place in the tendon and the muscle.
It is important to understand that when a muscle stretches, the tendon also stretches. It is
very elastic tissue and can withstand great tension. When activated, the Golgi tendon
organs trigger the antagonist muscle groups to stop the movement and to inhibit the
agonist muscle contraction. This response occurs to avoid possible injury to the muscle–
tendon relationship. Because of their actions, it is much easier to fully stretch a muscle
when the Golgi tendon organs are shut down.
Receptors are also located in the joint capsules and ligaments that relay information to the
brain, such as a change in position, speed of movement, or the acceleration of the limbs
that occur at the joints. These receptors are very sensitive and fire when a small change
(up to 2 degrees) occurs in joint position. Many pressure receptors exist that are very
active in posture. When any deviation in position occurs, they are fired so that a correction
can be made to bring you back into the normal position.
VISION
Related to kinesthesis is the use of visual reference points or visual cues when doing
exercises. For example, focusing on a particular object during an exercise enables you to
better balance the body and to keep yourself oriented to your surroundings. Try doing an
exercise with your eyes shut and notice how difficult it is to control your movements.
visual reference point: A chosen point of focus to aid in stability and balance.
The visual cue must be such that it does not change the position of your head, which also
relates to the balance mechanisms in your ears. For example, many weight trainees look
up at the ceiling when doing a squat in order to maintain an arch in the lower back. In so
doing, they have difficulty orienting the body. More effective is to have stronger back
muscles to maintain an arched position and to look directly ahead when doing the
exercise. You can then maintain the arch more easily and yet have good balance.
CONCLUSION
Now that you have a solid base of understanding with regard to muscles and muscle
functions as they relate to human motion, you can deduct that deviations in normal body
mechanics can adversely affect human movement and, more importantly, your clients’
fitness success. Before delving into the specifics of human movement and the relationship
between various muscles in the body, we will uncover postural deviations as they relate to
sound body movement.
Key Terms
acceleration
angle of pull
biomechanics
center of gravity
direction
first-class lever
force
fulcrum
gravity
inertia
kinesthesis
lever
line of action (also line of force)
line of gravity
magnitude
mass
momentum
moving inertia
point of application
power
range of motion (ROM)
resting inertia
second-class lever
stability
third-class lever
torque
velocity
visual reference point
work
Unit Summary
I. Biomechanics is the study of movement. More specifically, it is the movement involved
in a strength exercise or execution of a sports skill. It deals mainly with physical factors
such as speed, mass, acceleration, levers, and force along with the physical functions of the
movement.
A. Stability is the act of maintaining your body to ensure safety and effectiveness when
using free weights.
B. Muscular force is broken down into the components of magnitude, direction,
application of force, and line of force. It is exhibited in a push- or pull-type motion.
C. The angle of pull is the variance of force at different points in the range of motion of an
exercise. When you do a strength exercise, the strength exhibited at different points in the
range of motion will vary according to the angle at which the muscle pulls.
D. Work is defined by the equation W = F × D, where W= work, F= force, and D= distance
or displacement of the object being moved.
E. Power is defined as the work done in a unit of time.
F. Torque (twist) is rotary (angular) movement in any plane around an axis.
G. Newton’s first law of motion states that an object remains at rest or continues to move
with constant velocity in a straight line unless compelled by forces acting upon it.
1. Resting inertia means that when an object is at rest, it tends to stay at rest unless acted
upon by some outside force.
2. Moving inertia means that when an object is in motion, it will remain in motion unless
acted upon by some outside force.
H. Newton’s second law of motion deals with force and its relationship to mass and
acceleration. The greater the force and the greater the distance over which the force is
being applied (the weight is moved), the more work will be done.
I. Newton’s third law of motion states that objects in contact exert equal and opposite
forces on each other. This law can be demonstrated by jumping off a box. When you land
on the ground, your body applies a force against the ground and the ground in turn applies
an equal and opposite force against you to propel you into the air.
J. A lever is a rigid bar that turns around an axis of rotation or fulcrum and can be
categorized as first, second, or third class.
1. A first-class lever has its fulcrum or balance point between force and resistance.
2. A second-class lever is one in which the weight (resistance) is distributed between the
axis of rotation and application of force.
3. A third-class lever is one in which the force is applied between the axis and resistance.
K. Force transmission arrangements in the body include wheel and axle, pulley, pushing,
and pulling.
L. Gravity is the downward pulling force that creates resistance.
1. The center of gravity is the point in the body around which your weight is equally
distributed.
2. The line of gravity is the vertical line that falls from the center of gravity.
M. Kinesthesis is the ability to perceive your position and movement of the body or body
limbs in space.
N. Vision as it relates to kinesthesis is the use of visual reference points or visual cues
when doing exercises to better balance your body and to keep yourself oriented to your
surroundings.
UNIT 6
MUSCULOSKELETAL DEVIATIONS
TOPICS COVERED IN THIS UNIT
Understanding Good Posture
Benefits of Good Posture
Postural Self-check
Recognizing Postural Deviations
Role in Athletic Performance
Tonus
Spine
Feet
Pelvis
Conclusion
Unit Outline
I. Understanding Good Posture
A. Benefits of Good Posture
B. Postural Self-check
II. Recognizing Postural Deviations
A. Role in Athletic Performance
B. Tonus
C. Spine
1. Effects of Sitting on Spinal Posture
2. Workplace Ergonomics for Spinal Posture
D. Feet
E. Pelvis
Learning Objectives
After completing this unit, you will be able to do the following:



Know what good posture is, why it is important, and how to look for postural
misalignments in your clients.
Understand the importance of workplace ergonomics on spinal health.
Use your knowledge of posture to effectively design programs for clients with
musculoskeletal deviations.
UNDERSTANDING GOOD POSTURE
Posture is the way the body holds itself when sitting, standing, lying down, or moving. In
the past, the analysis of posture and exercises to correct posture were strongly
emphasized. In the present, posture appears to be mostly ignored. Proper musculoskeletal
alignment creates good posture. When you have good posture, your muscles and bones are
basically in balance and your body is symmetrical. When a deviation in posture exists, it is
often due to a lack of strength of particular muscles to hold the body in the needed
position. For example, weak erector spinae muscles of the lower back are the main culprits
in not being able to maintain an erect trunk in standing and walking, or maintain proper
back posture when lifting weights. As a trainer, you must learn to recognize good posture
and postural deviations in your clients and in yourself.
posture: The way the body holds itself when sitting, standing, lying down, or moving.
Most people with postural deviations are usually unaware of their posture. More startling
is that they show little concern about having good posture. However, for athletes and
fitness-minded people, posture should be of great concern. The reason is quite simple:
Posture can determine the outcome of performance and well-being. Before relating how
this can happen, it is necessary to first examine some of the benefits of good posture.
BENEFITS OF GOOD POSTURE
Good posture is important to health. It is needed in order to keep the organs in place and
to allow them to work efficiently and effectively. For example, if you have swayback, the
intestines press against the floor of the abdominal cavity instead of
being held in place. This position interferes with their normal work. If you have rounded
shoulders and an excessively rounded upper back, constriction occurs in the chest cage.
Because of this constriction, it becomes impossible to completely fill the lungs with air,
which is vital in athletic performance and fitness activities.
Posture affects how you walk, run, jump, lift weights, and execute other skills. For
example, if you have rounded shoulders, your arms may be slightly in front of your body
instead of hanging alongside your body. As a result, you may find that instead of lifting the
arms sideways directly overhead, you are lifting them up and in front of the body. This
adaptation changes the muscular movement and the movement pathway.
If you cannot hold your trunk erect during running, you will not have an effective push-off
or knee drive for a long stride length. Even in walking, if your feet or thighs are excessively
rotated outward, greater stress will be placed on the hip and knee joints. If walking in this
manner is carried on for a long period of time, injuries to these joints can occur.
Posture plays an important role in the prevention and rehabilitation of back problems. For
example, tight hip flexors may keep your pelvis tilted forward, causing swayback. If the hip
flexors are too weak while the abdominal muscles are strong, it may cause flattening of the
curve in the lower spine. If the upper portion of the hamstrings is too tight, they do not
allow you to hold the arch in your lower back when doing exercises such as the squat, or
when bending over to lift something. When your abdominal muscles are too tight, they
may flatten the spine, which places excessive pressure on the anterior aspects of the spinal
discs. If they are too weak, they may cause swayback.
By strengthening and stretching the necessary muscles to create good posture, you not
only prevent injuries but also rehabilitate them. Merely correcting posture is often all that
is needed in order to relieve back pain. For example, pulling the head back into proper
alignment is often sufficient to produce the normal curvature of the vertebral column. By
lifting the head and looking forward, you can activate the low-back muscles to hold the
spine in place and alleviate the problem.
Good posture makes you feel good. Because of its many benefits, such as ease of
movement, good balance of muscle strength and flexibility, proper positioning of the
spine, and proper functioning of the internal organs, your body feels good and you feel
good. You feel vibrant, confident, and ready to perform. Thus, posture should be of prime
focus in all fitness activities.
Posture is dynamic. Good posture is relatively easy to attain and maintain. Part of creating
good posture is learning new habits of sitting, standing, and walking. However, the major
factor is strengthening the key muscles that hold you in the proper posture.
Figure 6.1 Postural self-check
POSTURAL SELF-CHECK
Knowing the status of your own posture will help you to assess the posture of your clients.
To assess your posture, perform this self-check (see Figure 6.1):
Stand with your back against a wall. Your heels, backs of the calves, buttocks, upper back,
and head should comfortably touch the wall. If you must strain to make all points of
contact, then you probably have some deviations.
Also effective is to secure a string to the ceiling and hang a weight at the end of the string.
Stand so that the string is lined up with your nose, and then have a front-view picture
taken (or look in a mirror). Notice whether your shoulders are leaning to one side or
another or if more of your body is on one side of the line. With good posture, you should
be symmetrical on both sides of the string.
To get a graphic representation of how your weight is distributed in front of you and
behind you, try lining up the string in the middle of your shoulder down to the floor. This
method of postural self-check also shows whether you have any major deviations in spinal
curvature or positioning of the hips.
RECOGNIZING POSTURAL DEVIATIONS
The relative strength and flexibility of the spinal muscles play a role in the alignment of the
trunk and pelvis. When imbalances exist, three abnormal conditions
result: lordosis, scoliosis, and kyphosis. Table 6.1 includes these conditions as well as
other muscle misalignments and summarizes the muscles involved in them. Figure 6.2
illustrates these conditions as well as proper posture for comparison. When you learn to
recognize these imbalances in your clients and where they come from, you can help them
take steps to improve their posture.
lordosis: A spinal disorder in which the spine curves significantly inward at the lower
back. Also called ‘Swayback.’
scoliosis: A spinal disorder in which there is a sideways curve to the spine. The curve is
often S-shaped or C-shaped.
kyphosis: A spinal disorder which is characterized by an abnormally rounded upper back
(more than 50 degrees of curvature).
Table 6.1
Postural Deviations and Associated Muscle Imbalances
MALALIGNMENT POSSIBLE TIGHT
MUSCLES
POSSIBLE WEAK
MUSCLES
Lordosis
Lower back (erectors), hip
flexors
Abdominals (especially
obliques), hip extensors
Flatback
Upper abdominals, hip
extensors
Lower back (erectors), hip
flexors
Swayback
Upper abdominals, hip flexors
Oblique abdominals, hip
extensors
Kyphosis
Internal oblique, shoulder
adductors (pectorals and
latissimus), intercostals
Erector spinae of the thoracic
spine, scapular adductors (mid
and lower trapezius)
Forward Head
Cervical extensors, upper
trapezius
Neck flexors
Figure 6.2 Postural deviations
In lordosis, the superior iliac crests of the pelvis move forward and downward from the
normal anatomical position. This position is known as anterior tilt of the pelvis. In most
cases, the hip flexor muscles are shortened and the abdominal muscles are lengthened or
severely relaxed.
In posterior pelvic tilt, the hip flexor and low-back muscles stretch while the abdominal
and hamstring muscles shorten. Posterior tilt is not as common as anterior tilt and is
rarely brought about by lack of muscular strength. Both anterior and posterior pelvic
tilt place the lumbar vertebrae in potentially dangerous positions because of increased disc
pressure and a change in the line of gravity of the trunk.
In scoliosis, excessive lateral curvature of the spinal column exists. If the curvature is
relatively minor, you can do exercises to stretch the concave side and strengthen and
shorten the convex side of the curve. These exercises usually bring about straightening of
the spine. If rotation of the vertebral column also exists, the affected abdominal oblique or
erector spinae muscles must be strengthened.
Kyphosis is an exaggerated anterior-posterior curvature of the spinal column. It occurs
most frequently as excessive forward bending of the thoracic area and is seen most
frequently in older adults. It is usually associated with osteoporosis and osteoarthritis and
can result in the hunchback position. It also appears to occur more frequently with
younger adults as a result of practicing poor posture and performing an excessive number
of crunches through a shortened range of motion.
The term flatback is used frequently in conjunction with a kyphotic condition because the
exaggerated curvature of the thoracic spine creates a reduction in the natural lumbar
curvature. The flattening creates a posterior tilt condition of the pelvis.
Rounded shoulders are sometimes associated with kyphosis of the thoracic vertebrae, but
it is not the same condition. A round shoulder condition is technically abduction or
protraction of the scapulae. This position creates a “hollow” chest condition. You can have
abducted scapulae without having a kyphotic condition, or you can have both conditions.
ROLE IN ATHLETIC PERFORMANCE
Most people have some alignment deviation. As a result, the body does not work at
maximum efficiency. It is analogous to a machine. When a machine is properly aligned,
the working parts act efficiently. The machine will last much longer than one that is out of
alignment. In a misaligned machine, wear and tear on the bearings increases and stress
and strain on the working parts produce general depreciation.
As with any machine, when optimal performance is desired in the body, you must pay
attention to the alignment of the body parts. The balance of all the muscles acting on any
joint or body part affects proper maintenance of alignment.
Faulty posture indicates a shift of a body segment in relation to the other segments. In
addition, a shift of joint positions (or alignment) occurs in relation to the normal
gravitational line. Under optimal conditions, all body segments are lined up properly so
that undue stress does not fall on any one particular joint. When misalignment exists,
stress is placed on particular joints. For example, if your shoulders drop forward, your
head goes back and
your pelvis rotates to the rear. If you constantly lean to one side, your pelvis tilts sideways
and your spine curves to the opposite side, sloping one shoulder. Therefore, if you assume
and maintain an out-of-line position, your body must adjust the controlling ligaments and
muscles. In other words, if one body part is out of alignment, another body part must
likewise get out of alignment in order to balance it. Keep in mind that approximately 75 to
80 percent of the work of the muscles is involved in merely obtaining and maintaining
joint stability.
A high development of the agonists–antagonist function is essential to the development of
coordinated, skilled movement since antagonists control the speed, range, and force of the
action of agonists. This is true of the main muscles involved and of all the stabilizers of the
joints that are activated. This includes the stabilizer muscles that hold the joint of the nonmoving part in place to allow for movement at the other end of the muscle. Good balance
must exist between the opposing muscles.
When you have faulty posture, the normal length of the opposing muscles is changed so
that if one is shortened, its opposing muscle must be stretched or lengthened.
Therefore, any skill that you execute is affected by the performance of these muscles.
When faulty posture exists, movement is abnormal.
For example, if you have round shoulders, you may have adaptive shortening of the
pectoralis major and the serratus anterior, as well as tight anterior shoulder joint
ligaments. The opposing muscles (the mid-lower trapezius and rhomboids) are
overstretched. Thus the scapulae will not only swing apart but also rotate, resulting in the
lowering of the tips of the shoulders. Consequently, the more muscle mass is developed,
the greater the force that is applied to the joint. Because of this relationship, the stress on
the joint increases and the imbalance is increased even more.
Two factors operate in round shoulders. First, the arm weight and head weight fall forward
of the line of gravity. Therefore, an increase in the dorsal curve of the spine must
compensate. In turn, this increase must be balanced by a forward position of the pelvis
and increased lumbar lordosis (arching). Such a shift of body weight onto the forefoot
tends to increase pronation and depression of the foot arch.
Second, all arm work (shot put, discus, javelin, baseball pitching, golf swing, or exercise
execution such as the bench press or dumbbell fly) will show decreased efficiency, because
the weakened rhomboids have become long and the pectorals short. As a result, the arm
cannot be moved back to the maximum shoulder joint range, because the contractile
length of the pectoralis major will not allow it.
Deficiencies can also be seen in the shoulder girdle rotation (e.g., when twisting with a
barbell on the shoulders). This is because the spinal column cannot rotate on a “straight”
axis, as the spine is now bent. Thus more attention should be given to the antagonist
musculature instead of only trying to develop the agonist. You must restore the muscle
balance. This is essential to arm and shoulder girdle performance.
In the lumbar area, you must strengthen the abdominal muscles, especially the internal
and external oblique muscles that are mainly responsible for forward shoulder rotation
and flattening the abdominal wall. In addition, you must stretch and strengthen the
erector spinae by doing back raises to a position above level. You can also do the reverse
sit-up and reverse trunk twist to stretch the erectors even more, and at the same time
strengthen the abdominal muscles. Other muscle group pairs should be corrected in a like
manner if there is any imbalance.
The key to having a well-aligned and balanced body is to proportionally develop the
muscles (agonists) on one side of the joint with the muscles on the other side of the joint
(antagonists). This way the muscles will keep the joints in their natural state and prevent
deviations from occurring, allowing for more efficient and sustainable athletic
performance.
TONUS
Muscular tonus is associated with blood circulation and economy in movement.
Improper alignment results in additional muscular effort and strain, especially since it
creates rotary movements at the various joints. If excess muscular effort is sufficient to
produce fatigue, it can eventually affect your health. In more severe cases, the strain on the
joints can be sufficient to alter structure. There is also evidence to indicate that chronic
strain contributes to the development of arthritic types of ailments in later life. Such
alterations mean limited use of body parts and continued fatigue and strain.
muscular tonus: A state of partial contraction present in a muscle in its passive state
which, in skeletal muscles, aids in the maintenance of posture and in the return of blood to
the heart.
SPINE
The spine is the keystone of body structure. It must support the weight of the head, trunk,
and upper extremities. In addition, it is the solid point of attachment for most of the
muscles, anchoring and controlling the pectoral-shoulder girdle as well as the latissimus
dorsi and other muscles of the back, which move the arm. These functions require a
strong, well-supported spinal unit. In addition, the spine encloses and protects the spinal
cord and the nerves, which lead to and from it.
To allow for its functions, the spine should be firm, carefully articulated, and not too
flexible. You should be able to maintain the four natural curves of the spine at all times.
The ROM will vary from person to person but in general, it should be approximately 30 to
40 degrees of spinal flexion forward and 15 to 20 degrees of spinal extension to the rear.
Going beyond these limits is usually indicative of excessive flexibility, which leads to
additional spinal problems.
Effects of Sitting on Spinal Posture
Perhaps the most common oversight that bodybuilders and other athletes make is failing
to consider the risks of day-to-day, non-training activities. Typically, most trainees will be
very careful about their form when exercising (which comprises, at most, 20 percent of all
daily activities), yet totally ignore the potential consequences of other activities that make
up a much greater portion of our lives. When problems arise, blame is usually assigned to
the training activity.
Everyone spends a considerable amount of time sitting. Given this fact, it is prudent to
study this postural position and, in particular, its effects on the spine. People are usually
surprised to learn that pressures on the vertebral discs are higher when sitting than when
standing or lying down. In fact, some experts suggest that intradiscal pressure when
seated is up to 11 times greater than when lying down. This risk is particularly insidious
because sitting is not normally associated with back pain, whereas standing often is.
Figure 6.3 The spine
Many people who experience back pain while standing for long periods of time will feel
better when they sit down. It is difficult for them to understand just how sitting can place
undue pressure on the vertebral discs. In order to understand this concept better, consider
the following facts:
First, the distinction must be made between the back muscles and the vertebral discs.
When you stand for long periods, the disc pressure is relatively low, but you nevertheless
feel pain. The pain results from fatigued low-back muscles.
Second, increased pressure on the discs in and of itself does not necessarily cause
immediate pain. Thus, people are often unaware of this pressure, which in the long term
can lead to deformative changes in the discs.
Now to the real mystery: How can sitting create higher intradiscal pressure than
standing? It is because when standing, your body weight is distributed over a wide variety
of structures, including muscles, tendons, ligaments, and joints. Upon sitting down,
however, the abdominal “corset” relaxes, which causes a majority of your body weight to
load the discs. As mentioned earlier, you probably will not feel any pain at all when this
happens. Over the long term, though, the constant, increased load upon the discs can
result in a multitude of problems, from impinged nerve roots to degenerative
osteoarthritic changes.
intradiscal pressure: Pressure present between vertebral disks.
Workplace Ergonomics for Spinal Posture
Because sitting is inescapable for most people, the best advice is to (1) limit time spent
sitting as much as possible, and (2) design your workplace with the following in mind:
ergonomics: A science that deals with designing and arranging things so that people can
use them easily and safely.






Chairs with lumbar supports (sufficient to maintain but not exaggerate the normal
lordosis, or sway, of the spine) have been shown to lower intradiscal pressures compared
to chairs without these supports.
Chairs with arm rests also reduce pressure on the discs.
Sitting in a reclined position (120 degrees is optimal) lowers disc pressure, so make sure
your chair allows you to alternate positions.
Since keeping the knees close together makes you more prone to “slumping,” choose a
chair that is wide enough to keep your knees apart. Also, if you sit at a desk for long
periods of time, make sure that it allows you enough space to open your knees.
When selecting a chair, adjustability is crucial. Because people come in different shapes
and sizes, they have unique needs for their workstation setup. An adjustable chair will
ensure that you can optimize your own workstation for the best possible ergonomic effect.
At your workstation, your chair and desk arrangement should be such that your forearms
rest on the desk with your elbows at a 90-degree angle close to your sides. This position
reduces stress on the trapezius and surrounding muscles of the upper back and neck.
Spinal disorders are preventable! Although the dangers of sitting for prolonged periods of
time may not seem like a pressing issue at the moment, it has a cumulative effect on the
spine over the years.
FEET
Seemingly small, insignificant deviations can lead to major changes in the entire body. For
example, if the feet are not sufficiently strong to keep the body in balance and the shins in
line with the feet, the knees can change their position. This change can affect the hips,
which in turn will affect the spine, which can then affect head position. Each joint will then
be limited in the actions that it is capable of, especially when the deviation is coupled with
tight muscles on one side and weak muscles on the other.
Even being able to balance your weight has a very profound bearing on the feet. How the
legs are used in activities such as running is directly related to the influence of the joints,
ligaments, and muscles in the limbs above it. Thus, any problems in the lower body affect
the upper body and vice versa.
For example, many athletes including bodybuilders have a lateral tilt of the pelvic girdle.
This tilt usually occurs to compensate for deviations above or below the pelvis. Studies
have shown that up to 50 percent of individuals can have a lateral tilt of the pelvis of 1/4
inch or more. It can be caused by having one arch of the foot lower than the other, greater
angulation of the knee on one side, an increase or decrease in the angle on the neck of the
femur (the angle that the bone runs from the hip to the knee in a normal standing
position), rotation of the femoral shaft (which can have the knee pointed outward or
inward), and the size and shape of one ilium (flat bone on either side of the pelvis) as
compared with the opposite one.
Such asymmetry and tilting of the pelvis will result in asymmetrical muscle lengths and a
tilt in both hip axes, which produce an eccentric action between the two joints. The
transmission of weight and forces acting on the legs and feet will be different.
Consequently, the wear and tear on the ligaments and joints will be different.
PELVIS
Even more common among bodybuilders and athletes is a forward tilt of the pelvis, which
results when the upper pelvis drops forward, resulting in excessive arching of the lower
spine. If this is coupled with a slight lateral tilt of the pelvis, there is torsional force from
the twisting of the spinal column. When this occurs, one hip socket as well as one side of
the hip will be further forward than the other. In this case, the hip-joint flexor muscles will
be shortened and the lower back muscles will be tightened.
Excessive arch in the lower back can result from low-back problems or from deviations of
the pelvic girdle. The pelvis and spine are so interrelated that it is almost impossible to say
which is primarily at fault in causing any particular problem. However, note that the
vertebral column is flexible and often compensates for any pelvic faults by changing
position in corresponding planes. In a well-muscled person these changes can be easily
overlooked.
An increase in the forward tilt of the pelvis in relation to the adaptive shortening of the hip
flexors and the lower trunk extensors upsets the normal antagonism in the forward and
backward direction. But this antagonism must be brought into a balanced action for the
best performance when lifting weights. In this case, shortening the abdominal muscles in
front and the gluteal muscles in back is essential to attaining the best position of the pelvis
in relation to the trunk.
In addition, the hip lifting action of the quadratus lumborum and latissimus dorsi hold the
leg on the same side up during the swing phase in walking and running, while the
rotational action of the internal and external obliques brings that side of the hip forward.
Not only must the one side be pulled forward, but the alternating action of the opposite
oblique must also relax enough to allow the serratus anterior and the shoulder girdle to be
rotated backward. The balance of these trunk muscle torque groups is a vital element in all
locomotor progression.
When there is any structural pelvic asymmetry, there cannot be symmetrical action of the
lower trunk muscles because of the torque in the pelvis and the compensatory curvature
and torque of the spinal column. The latissimus dorsi, quadratus lumborum, iliopsoas, and
abdominal obliques are all affected, and there must be an imbalance in the length and
strength of the contralateral muscles.
CONCLUSION
Deviations in the musculoskeletal system must be assessed and then modified to correct or
prevent further deviation from occurring. Now that you can accurately assess some of the
more common deviations that you may encounter with your clients, you are ready to learn
about the musculoskeletal system, including joint action, joint makeup, muscle
involvement, and the associated relationships between various muscle groups in the body.
Key Terms
ergonomics
intradiscal pressure
kyphosis
lordosis
muscular tonus
posture
scoliosis
Unit Summary
I. Musculoskeletal deviations can result in poor muscle balance, poor flexibility, and
improper spinal alignment, and they can predispose you to injury.
A. When you have good posture, your muscles are in balance and your body is
symmetrical.
1. Good posture makes you feel good. Because of its many benefits, such as ease of
movement, good balance of muscle strength and flexibility, proper positioning of the
spine, and proper functioning of the internal organs, your body feels good, therefore you
feel good.
2. To evaluate your posture, stand with your back against a wall. Your heels, backs of
calves, buttocks, upper back, and head should comfortably touch the wall. If you must
strain to make all points of contact, then you probably have some deviations.
3. The relative strength and flexibility of the spinal muscles play a role in the alignment of
the trunk and pelvis. When imbalances exist, three abnormal conditions can result:
lordosis, scoliosis, and kyphosis.
4. The key to having a well-aligned and balanced body is to proportionally develop the
muscles (agonists) on one side of the joint with the muscles on the other side of the joint
(antagonists). Only in this way will the muscles keep the joints in the natural state and
prevent the occurrence of deviations.
5. Muscular tonus is associated with blood circulation and economy in movement.
6. The spine is the keystone of body structure. It must support the weight of the body.
a. Intradiscal pressure when seated is up to 11 times greater than when lying down.
b. Sitting is inescapable for most people, so the best advice is to (1) limit time spent sitting
as much as possible, and (2) design your workplace according to correct ergonomics.
7. For correct ergonomics, feet must be sufficiently strong to keep the body equally
balanced and the shins in line with the feet, head, trunk, and upper extremities.
8. Pelvic asymmetry results in a deviance of symmetrical action in the lower trunk muscles
because of the torque in the pelvis and the compensatory curvature and torque of the
spinal column.
UNIT 7
MUSCLE MECHANICS
TOPICS COVERED IN THIS UNIT
Introduction
Knee
Muscles of the Knee Joint
Ankle and Foot
Muscles of the Ankle Joint
Spine
Muscles of the Spine (Midsection)
Shoulder
Muscles of the Shoulder Joint
Shoulder Girdle
Elbow
Relationship Between the Shoulder and the Elbow
Forearm
Radioulnar Joint
Wrist
Muscles of the Wrist Joint
Conclusion
Unit Outline
I. Introduction
II. Knee
A. Muscles of the Knee Joint
1. Relationship Between the Gastrocnemius and the Hamstrings
2. Relationship Between the Quadriceps and the Hamstrings
III. Ankle and Foot
A. Muscles of the Ankle Joint
IV. Spine
A. Muscles of the Spine (Midsection)
1. Relationship Between the Abdominal Muscles and the Hip Flexors
V. Shoulder
A. Muscles of the Shoulder Joint
B. Shoulder Girdle
1. Relationship Between the Shoulder Joint and the Shoulder Girdle
VI. Elbow
A. Relationship Between the Shoulder and the Elbow
VII. Forearm
A. Radioulnar Joint
VIII. Wrist
A. Muscles of the Wrist Joint
1. Relationship Between the Wrist Muscles and the Elbow
IX. Conclusion
Learning Objectives
After completing this unit, you will be able to do the following:


Identify the functions of the musculoskeletal system in the body.
Understand how to apply knowledge of muscle mechanics to exercises.
INTRODUCTION
Exercises are usually described in very general terms in books, magazines, and websites.
These generalities lead to misunderstandings, which more often than not lead to injury.
However, an exercise analysis answers questions such as these:
If the exercise is effective, why is it effective?
What is the role of each joint action?
Which actions can be changed to make the technique more effective?
How can joint body or limb movements be changed to bring in greater involvement of
specific muscles?
How can specific actions be made more powerful?
Should the exercise be modified? If so, how?
Most sources of standard instruction fail to address important points such as these. The
most accurate way to determine the key actions and muscles involved in a strength
exercise is to analyze movement in terms of kinesiology and biomechanics. Only in this
way can you, as a future fitness educator, determine which joint actions and muscles play a
major role and whether the exercise is effective and safe.
This unit discusses muscle mechanics for the major joints and muscle groups that are
involved in personal training. It looks at the musculoskeletal system with regard to joint
action, joint makeup, muscle involvement, and the associated relationships between
various muscle groups in the body.
KNEE
The knee joint is made up of the end of the femur and tibia bones. The ends of these bones
consist of two shallow convex surfaces into which semicircular-shaped femoral condyles
fit. Because of the shape, the bony stability of the knee is extremely weak. To improve
stability, many ligaments surround the knee joint. For example, the posterior cruciate
ligament prevents forward displacement of the femur on the tibia. The anterior cruciate
ligament prevents backward displacement of the femur on the tibia. The medial and lateral
ligaments provide stability on the medial and lateral sides. The knee joint is stabilized
posteriorly by the popliteal ligament and anteriorly by the patellar ligament.
The knee joint must allow movement yet be stable enough to absorb and withstand the
forces created by the weight of the body and the forces generated while participating in
various activities. For example, the knee must counteract the negative landing forces in
running and jumping and in weightlifting exercises.
Because of the roles the knee must play, ligament and muscular stability assume
important roles. For example, when the knee is extended, it remains stable because it is
surrounded by fairly taut ligaments from all sides and from within. However, when the
knee is flexed, some of the ligaments loosen to allow for greater movement. Because of this
response, the muscular arrangement around the knee is extremely important in
maintaining the stability needed in order to prevent injury.
The knee is stabilized on the anterior side by the quadriceps, on the medial side by the
sartorius and gracilis, on the lateral side by the tensor fasciae latae (TFL), and on the
posterior side by the hamstring muscle group from above and the gastrocnemius from
below. Because of the small angle of attachment of the quadriceps to the tibia, a large
stabilizing component is always acting on the knee joint. This is particularly important
when the hamstrings are contracting strongly and the knee is flexed beyond 90 degrees, at
which point the hamstrings have a backward dislocating component. To counteract this
force, there is usually hip flexion, which serves to maintain hamstring length so that
tension is maintained.
When the leg is bent 80 to 90 degrees or more and the sartorius, gracilis, and
gastrocnemius muscles contract, they create a dislocating component at the knee joint.
From 180 degrees (straight leg) to 90 degrees of flexion (bent leg), most of the muscles
crossing the knee provide a rotary and stabilizing effect. When knee flexion is
Figure 7.1 The knee joint, anterior view
less than 90 degrees, a dislocating component occurs in some of the muscles. The knee
also has weak bony and ligamentous arrangements, increasing its vulnerability.
The major movements that are possible in the knee joint are flexion and extension. Medial
rotation and lateral rotation take place only when the knee is flexed. This configuration
allows the foot to turn when it is free to move, and the trunk to turn when the foot is fixed
to the ground, such as when wearing cleats or spikes. If rotation occurs when the leg is
straight, it may cause knee injury.
MUSCLES OF THE KNEE JOINT
The muscles of the knee joint are predominantly two-joint muscles, which also cross
and act at the hip joint. They include the hamstrings, rectus femoris of the quadriceps
group, gracilis, sartorius, and TFL muscles. The gastrocnemius is another two-joint muscle
of the knee, which also crosses the ankle joint. The two-joint muscle arrangement provides
efficiency of movement in walking and running. However, a two-joint muscle cannot
stretch enough to allow full range of motion at both joints at the same time. Nor can it
contract enough to produce complete movement at both joints at the same time. A
common example is when you try to flex the hip and extend the knee fully at the same time
or to simultaneously extend the hip and flex the knee fully. The hamstrings cannot
contract or stretch enough to allow either of these combinations to be performed in total.
Although the hamstring muscles are usually considered as one group, important
differences exist between them. The biceps femoris (attached on the lateral side) and the
semimembranosus and semitendinosus (attached on the medial side of the knee) produce
lateral and medial rotation, respectively, when the knee is flexed. If an imbalance in
strength exists, such as when the biceps is stronger than the semimembranosus and
semitendinosus, lateral rotation at the knee occurs during knee flexion.
You can see this relationship when doing leg extension and leg curl exercises. The
hamstrings work to
Figure 7.2 Muscles of the knee joint
flex the knee. But because of the imbalance, the biceps femoris overpowers the
semimembranosus and semitendinosus and causes the lower leg to be laterally rotated as
the knee is flexed. To correct this condition, you must work the hamstrings while keeping
the lower legs medially rotated. If the medial hamstring muscles are weaker than the
lateral muscles, the lower leg will be medially rotated, as it swings forward.
two-joint-muscles: Muscles that cross two joints rather than just one, such as the
hamstrings, which cross both the hip and the knee.
A similar situation exists when an imbalance occurs in the strength of the quadriceps
muscles, particularly the vastus medialis and lateralis. The vastus muscles must be strong
enough to stabilize the patella and keep it in its groove during knee extension, especially in
forceful contractions of the quadriceps. If the vastus medialis is weak, the patella becomes
laterally displaced because of the pull of the vastus lateralis. In this case or if the reverse
imbalance exists and continues over a long period of time, it can
cause chondromalacia (degeneration of cartilage).
chondromalacia: The degeneration of cartilage.
Relationship Between the Gastrocnemius and the
Hamstrings
The gastrocnemius, the major muscle of the posterior shin, functions to extend the foot
(plantar flexion). It ties in with the hamstrings at the knee joint where they are both
involved in knee joint flexion. In addition, the insertion of the gastrocnemius on the femur
helps to provide greater stability.
To be most effective, the gastrocnemius must be taut in order to have a strong contraction
at the knee joint. This means you must put the foot into flexion (dorsiflexion) in order to
stretch the Achilles tendon and to make the gastrocnemius muscle taut. Thus, when it
contracts, it will shorten the upper tendons at the knee immediately. In this case, the
muscle shortening will not result in taking up the slack of a relaxed Achilles tendon if the
toes are pointed when the knee flexion takes place.
The practice of putting one end of a two-jointed muscle on stretch in order to elicit a
strong contraction at the other end is very important for maximal development of twojointed muscles. These muscles include the hamstrings, the rectus femoris of the
quadriceps group, the biceps, the long head of the triceps, and others.
Relationship Between the Quadriceps and the
Hamstrings
It is not uncommon to hear that the strength of the hamstrings must equal that of the
quadriceps. Many personal trainers and strength coaches strive to create an equal balance
of strength between these two muscle groups. However, the quadriceps should always be
stronger than the hamstrings in almost all instances. The exact ratio should depend on the
angle in the knee and the position of the thigh at the hip joint.
For example, the quadriceps has four separate muscles, three of which are fairly large. The
muscle mass of the quadriceps is much greater than that of the hamstrings, and its
workload is also much greater. The quadriceps muscles are antigravity muscles that must
contract to not only keep you erect but to move you in walking, running, and jumping
activities. The hamstrings (at the knee joint) are hardly involved in these activities. In
regard to size, only one of the hamstrings (the biceps femoris) has two heads and a
substantial amount of muscle mass. The semitendinosus and semimembranosus have very
small muscle bellies; thus, from the sheer size of the quadriceps and its functions, it stands
to reason these muscles should be stronger.
Figure 7.3 Hamstring group and quadriceps group
Note that at the hip joint, the hamstrings are stronger than the one muscle of the
quadriceps (rectus femoris). Also, other muscles come into play at the hip joint for both
flexion and extension.
In the knee joint (leg) extension exercise, all four heads of the quadriceps are involved.
Since the rectus femoris is a two-jointed muscle, the hip end must be placed on stretch for
the lower end to act strongly at the knee. If not, the main function of the remaining three
heads (vastus lateralis, vastus medialis, and vastus intermedius) is knee joint extension.
They are not affected by the position of the leg at the hip in order to have an effective or
maximal contraction.
The rectus femoris (the two-jointed muscle of the quadriceps group) plays a major role in
knee joint extension when it is placed on stretch at the hip joint. To do this, the leg must
be in line with the body when the knee joint extension takes place. If you are in a seated
position (in which most testing and exercise is done), there is slack at the upper end of the
rectus femoris. When it contracts in knee joint extension, the initial shortening takes up
the slack of the upper muscle tendons and, as a result, its contribution to knee extension is
not as great as possible.
For a stronger contraction of the hamstrings in the knee (leg) curl exercise, the hip joint
end of the hamstrings must be placed on stretch. (This is why the seated knee curl seems
easier than the more popular lying variant). However, the hamstring muscles cannot
generate the same amount of strength exhibited by the quadriceps (all other training
factors being equal).
More important than the strength ratio between the quadriceps and the hamstrings is to
develop these muscles as needed for bodybuilding or for sports performance. Keep in
mind that as you increase the strength of the quadriceps, you are then capable of getting
greater strength of the hamstrings and vice versa. Thus, both of these muscles should be
fully developed.
ANKLE AND FOOT
The ankle joint is made up of the tibia and the talus bones. Because the end of the tibia is
somewhat concave and the talus below it is convex, the bony stability is fairly strong. Since
the ankle must withstand great stress, strong ligaments surround the joint to provide even
greater stability.
Movements possible at the ankle are flexion (dorsiflexion) and extension (plantar flexion).
The axis of rotation for the ankle is not in a true frontal plane. It is oriented slightly
backward and downward on the lateral side. The tilt creates a slight disorientation of the
foot from true anterior–posterior plane motion during plantar flexion
Figure 7.4 Muscles of the ankle and foot
and dorsiflexion; in other words, the foot does not remain in the same position during its
up-and-down movement.
The subtalar joint is located between the talus and calcaneus. This joint is typically
involved in ankle sprains or strains. It is an intertarsal joint (involves several bones of the
foot), while the ankle joint has only two bony parts: one in the shin and one in the foot.
The subtalar joint allows for various positions of the foot and leg in response to weight
bearing, particularly when running on uneven or curved paths. It is the main connection
between foot mobility and stability of the ankle and leg.
In plantar flexion, there are simultaneous movements of the foot around the subtalar and
ankle axes (i.e., a combination of eversion at the subtalar joint and extension at the ankle
joint). There is a combination of inversion at the subtalar joint and dorsiflexion at the
ankle when executing ankle joint flexion.
Having muscle strength on both sides of the ankle and foot is important in maintaining
joint integrity. Any imbalances in the strength or flexibility of the surrounding
musculature result in misalignment. This in turn must be counteracted by muscular
contractions or ligament tension. If not, postural imbalances occur.
People with shin splints usually have significantly greater plantar flexor (extensor)
strength than dorsiflexor (flexor) strength and greater movement of the calcaneus during
the support phase of walking and running. Overdevelopment of the ankle extensors tends
to also cause a muscular imbalance between the strength of the foot supinator and
pronator muscles, which may result in lateral ankle sprains, particularly when landing
after being airborne.
MUSCLES OF THE ANKLE JOINT
The gastrocnemius is the major ankle extensor muscle of the shin. It is located on the
upper posterior side of the lower leg and gives the rounded form to the calf. At the upper
end are two tendons that attach to the posterior side of the condyles of the femur, while at
the lower end, the tendons from the two heads of the muscle run diagonally downward to
attach to the Achilles tendon.
Lying directly beneath the gastrocnemius is the soleus, which has similar functions to the
gastrocnemius. Its upper attachment is on the tibia and fibula and its lower attachment
blends into the Achilles tendon on the calcaneus. The soleus is slightly wider than the
gastrocnemius, and together they form a functional unit sometimes called the triceps
surae. Collectively, these muscles are extremely strong; when combined with the Achilles
tendon, they are even stronger. They can exert a force of over 900 pounds in ankle
extension.
The tibialis anterior is the main muscle on the anterior side of the shin. Its muscle mass is
located high on the shin, while its tendon at the lower end crosses the ankle joint and
inserts on the inner and under surface of the foot arch. This is one reason why the tibialis
anterior not only dorsiflexes the foot but also turns the sole of the foot inward. It plays a
major role in maintaining the foot arch.
SPINE
The most important functional unit of the body is the vertebral (spinal) column. It
provides the main framework and foundation for most of the movements of the body and
extremities. The spinous and transverse processes serve as attachments of the deep and
superficial muscles of the back, which produce forward, backward, and lateral bending,
and small amounts of rotation of one vertebra on another. The sizes of the processes and
the corresponding muscles increase as you move down the vertebral column, and they are
largest in the lumbar area.
The movements of the spinal column include movements of one vertebra on another
separated by the intervertebral discs. There are also movements between the facets of
successive vertebrae, which are freely movable. The intervertebral discs allow slight
movement and function in shock absorption. Although the joint between any two adjacent
vertebrae does not allow a great deal of motion, multiple vertebral joints produce a great
range of motion in flexion, extension,hyperextension, lateral flexion to both sides, and
rotation. Note that movement is limited in the thoracic area because of the attachment of
the ribs and the longer spinous processes on the thoracic vertebrae.
The vertebral column lacks great bony stability and relies to a great extent on the
ligaments and muscles for support. If they become stretched or weakened, the integrity of
the column is weakened and the vertebrae must absorb the forces. This force absorption
sometimes results in vertebral disc damage, especially in high impact activities.
The ligaments can hold the vertebral column together, but continued reliance on them as a
result of weak muscles or a strength imbalance between antagonist groups of muscles can
result in excessive stretching of the ligaments, which becomes permanent. This response
often occurs during excessive static or passive stretching and, as a result, damage may
occur to the discs and spinous processes.
MUSCLES OF THE SPINE (MIDSECTION)
The abdominal musculature (rectus abdominis, internal and external obliques, transverse
abdominis) acts to prevent the vertebral column from continually hyperextending. The
rectus abdominis (and, to a limited extent, the internal and external obliques) acts to pull
the anterior pelvis toward the sternum or to pull the rib cage down toward the pelvis. Both
of these actions result in spinal flexion in which the rectus abdominis has a large
Figure 7.5 Muscles of the midsection
stabilizing component because its line of action is parallel to the spinal column. The
obliques have a rotary component, but they cancel out this action when the muscles on
both sides of the abdomen simultaneously contract.
hyperextension: Extension of a limb or part beyond the normal limit.
From physiology, it is known that when a muscle contracts, the entire muscle undergoes
contraction. This is true of the abdominal muscles. However, because the rectus
abdominis is relatively long, one end is stabilized when it contracts in order to produce
movement in the other end. For example, when doing a sit-up or crunch, the pelvic girdle
is held in place firmly through contraction of the hip joint muscles so that the shoulders
will rise toward the feet. Because of this, you experience shortening mainly of the upper
fibers of the rectus abdominis. The lower fibers do not undergo the same amount of
shortening. For the most part, it remains under isometric contraction and, as result,
mainly the upper fibers develop.
To produce shortening of the rectus abdominis in the lower fibers of the abdomen, it is
necessary to do exercises such as the reverse sit-up (reverse crunch) or hanging leg raises.
In these exercises, the pelvic girdle is in motion while the chest and shoulders are
stabilized. The upper fibers of the abdominal muscles remain isometrically tensed.
This principle appears to hold true in all exercises involving relatively long muscles. A
distinct difference exists in the amount of shortening or the intensity of the contraction
that can be seen in different parts of the muscle. When the muscle is relatively short, it is
not noticeable. The biggest difference may be in the shortening of the tendons at the end
that is involved in movement.
The internal and external obliques are unique in their functions. For example, when the
right side of the external oblique muscle contracts, it pulls the shoulders down and to the
left. When the left side of the external oblique muscle contracts, it pulls the shoulders
down and to the right. The internal obliques on each side have an opposite function. When
both the internal and external obliques contract on both sides simultaneously, they cancel
out their rotational effects and the movement results in flexion.
Because the lower fibers of the internal oblique muscle are relatively horizontal, it does not
appear to play a major role in movements. Its main function appears to be to hold in the
abdominal viscera together with the transverse abdominis. However, it is still possible to
see some contraction in this area when the internal oblique muscles work together with
the external oblique muscles to produce full rotation of the shoulders (or hips if they are
free to move).
For example, if the pelvis is stabilized, contraction of the upper right external oblique and
the lower left internal oblique creates a long pull down and to the left. Contraction of the
upper left external oblique and the lower portion of the right internal oblique produces
strong downward rotation to the right. If the shoulders are stabilized and the hips are in
motion, then movement occurs in the opposite direction. For example, the left external
and the right internal oblique muscles rotate the right hip up and to the left while the right
external and left internal oblique muscles rotate the left hip up and to the right.
Because of the overlapping functions of most muscles of the midsection, they provide for
more safety and strength of the core area of the body. For example, in lateral movements
of the spine, not only are the abdominal muscles involved, but also the erector spinae and
the quadratus lumborum located on both sides of the lumbar spine. When the pelvis is in
motion the lower latissimus dorsi—which attaches to the upper, outer surface of the
pelvis—is also involved. Thus there is some interplay between the muscles of the
midsection together with the muscles of the back.
There is also some interplay between the pectoralis major and the external obliques. Note
that the fibers of the pectoralis major in the very lowest section run downward at an angle.
In certain European literature, this is considered the abdominal portion of the pectoralis
major. In the United States, trainers usually only distinguish the upper and lower fibers of
the pectoralis major and do not divide it into three sections.
Examination of the lower fibers of the pectoral muscles shows that the fibers run
downward and are almost in line with the external oblique fibers as they come close to one
another. Thus, as the lower portions of the pectoralis major contract, they may also tie in
with contraction of the external obliques to create movement across the entire anterior
trunk. For example, you can see it happen while doing chin-ups and pull-ups as your body
rises in front and when doing pull-downs across the body.
The deep musculature on the posterior spine is composed of many small pairs of muscles
that span one or more vertebrae. All of the muscles are situated so that they have large
stabilizing components. The larger muscles are collectively known as the erector spinae.
They run from the sacrum of the pelvis to the head and are angled out somewhat to cover
both sides of the spine. The erector spinae muscles are biggest and strongest in the lumbar
area. They hold the trunk erect and are involved in spinal extension, hyperextension,
lateral flexion, and rotation to the rear. Therefore, maintaining strength of the spinal
musculature is important throughout life.
The pelvis connects the trunk with the lower extremity. During weight-bearing exercises
when the legs are fixed, the pelvis changes positions relative to the femur. However, as the
pelvis moves on the thigh, the vertebral column must change position since it is connected
to the pelvis at the sacrum. When you are airborne or when the lower body is free to move,
the pelvis moves with movement in the lumbar spine. The legs may move as a unit with the
hips or individually.
The extensor muscles of the spine are called antigravity muscles. They apply forces on
the skeletal framework to counteract the pull of gravity. As a rule, they are responsible for
posture, especially an erect trunk position.
antigravity muscles: A hypothetical force by which a body of positive mass would repel
a body of negative mass.
The muscles of the hip joint also control movement of the pelvis. They are involved in all
movements of the pelvis when the axis is in the hip joint. When the axis is in the waist, the
midsection muscles are involved. Thus, a multitude of muscles are involved with
movement and stabilization of the pelvis and spine; they can be considered the core body
areas. By keeping the hip and midsection strong and the body parts in good alignment, you
can have a pain-free, mobile, and functional spine for your entire lifetime.
Relationship Between the Abdominal Muscles and the
Hip Flexors
The abdominal and hip flexor muscles work together in a manner similar to the hip
extensors and the erector spinae muscles of the lower back. The abdominal muscles
(rectus abdominis, external and internal obliques) and the hip flexors (iliopsoas,
pectineus, and rectus femoris) work together in order to create maximum ROM in your
ability to raise the legs as high as possible.
When you are in good alignment in a standing position and raise one leg (keeping it
straight), the hip flexor muscles contract concentrically to raise the leg approximately 30
to 45 degrees (more if you have great hip joint flexibility). As you raise the leg, the erector
spinae muscles remain under isometric contraction in order to stabilize the pelvis. When
the leg goes higher than the 30 to 45 degree angle, the pelvic girdle then
rotates posteriorly (upper hips move backwards) to allow the leg to rise higher. At this
time, the rectus abdominis and oblique muscles undergo concentric contraction in order to
rotate the hips, and the hip flexor muscles switch to an isometric contraction in order to
maintain the hip and leg position as a unit. The erector spinae muscles switch to an
eccentric contraction in order to control the rotation of the pelvis.
If you begin with the leg well behind the body, then the abdominal muscles will have to
first undergo a concentric contraction in order to rotate the pelvis posteriorly and bring
the leg in alignment with the body. The hip flexor muscles at this time remain under an
isometric contraction to stabilize the hip-leg unit. When the leg is vertical, the muscular
contraction switches and the hip flexors undergo a concentric contraction in order to raise
the leg while the pelvis remains stable with an isometric contraction of the erectors. In
some cases, you may find some residual abdominal muscle contractions and the pelvis
may move somewhat. But it will be little in comparison to movement of the leg.
SHOULDER
The bony arrangement of the shoulder joint consists of a shallow socket (glenoid fossa)
into which the spherical head of the humerus fits. Less than half of the humerus is in the
socket at any one time, and the bony arrangement is therefore weak. Because it is a balland-socket joint, the shoulder joint is a multi-axial joint (the same as in the hip joint) that
allows for the following movements: flexion, extension/hyperextension, transverse
(horizontal) adduction and abduction, abduction and adduction, medial (inward) and
lateral (outward) rotation, and circumduction. The shoulder joint is designed for mobility
and therefore sacrifices bony and ligamentous stability.
MUSCLES OF THE SHOULDER JOINT
The musculature surrounding the shoulder joint is arranged so that it produces large
stabilizing components especially by the four rotator cuff muscles (supraspinatus, teres
minor, infraspinatus, and subscapularis). Regardless of the position of the arm, the
anterior, posterior, and middle deltoids also have large stabilizing components because of
their small angle of pull. Further stability is provided by the long heads of the biceps
brachii on the anterior shoulder and the triceps on the posterior side. As with the deltoid
muscle, the upward pull of these muscles is counteracted by the downward pull of the
rotator cuff muscles (except for the supraspinatus).
Most of the other muscles surrounding the shoulder joint also exert a stabilizing force, but
their main function is to move the arm. In addition, as the arm moves into motion,
Figure 7.6 Muscles of the shoulder
the muscles involved change their angles of pull considerably. Thus they may not always
be major stabilizers or movers of the shoulder joint.
The muscles that serve as the primary movers of the arm at the shoulder joint are the
deltoid, coracobrachialis, pectoralis major, latissimus dorsi, teres major, the long and
short heads of the biceps, and the long head of the triceps on the posterior side. The
muscles located on the front of the chest and shoulder are involved mainly in flexion and
horizontal adduction, while those on the posterior side are involved mainly in extension
and horizontal abduction.
The latissimus dorsi and teres major muscles on the posterior side rotate the arm medially
at the shoulder joint. In addition, the infraspinatus and the teres minor, also located on
the posterior side of the humerus, act in a wheel-and-axle like mechanism to laterally
rotate the arm around the longitudinal axis of the humerus. The subscapularis, located on
the anterior side of the humeral head, also functions in a wheel-and-axle like mechanism
to medially rotate the arm. The supraspinatus is attached to the top of the humeral head
and functions as a first class lever to pull the top of the humeral head inward. As a result,
the humerus moves into abduction.
The latissimus dorsi and teres major are located mostly on the upper sides of the back and
insert on the front side of the humerus. When they contract, they pull the front of the arm
medially in a wheel-and-axle arrangement, extend the arm, and retract the shoulder
beyond the level of the back. In the wheel-and-axle arrangement, the wheel is represented
by the forearm and hand if the elbow is extended. The ROM of the hand when the elbow is
flexed during shoulder joint medial rotation varies depending on the amount of elbow
flexion. It is greatest at 90 degrees of elbow flexion and smallest when the arm is straight.
Consider this when doing rotator cuff exercises, especially when you hold a strength bar in
the hands.
The positioning of the arms is also important. When the arms are all the way to the rear of
the body and the scapulae are retracted (i.e., moved close together), the initial contraction
of the muscles on the front of the body (pectoralis major and anterior deltoid) move the
head of the humerus more to the front in order to produce horizontal flexion in the
shoulder joint. The posterior rotator cuff muscles counteract this forward force
component. Problems arise in the shoulder joint if the stabilizing forces are not effective in
counteracting the dislocating forces of the muscles involved in the movement.
The action of arm abduction is complex. The supraspinatus initiates the first few degrees
of shoulder abduction. It is a first-class lever arrangement which gives a better angle of
pull than does the deltoid muscle. The deltoid does not come into play until the arm is
approximately 45 degrees out to the side and up. As shoulder joint abduction takes place,
the scapula upwardly rotates in coordination with the arm movement. In general, the
scapula rotates about 2 degrees for every 3 degrees of arm movement. In this way, the
acromion process of the scapula is moved out of the way as the greater tuberosity of the
humerus gets close to it.
Shoulder impingement usually occurs in activities that require the arm to be abducted
or flexed and medially rotated, such as in baseball pitching. Also susceptible are tennis
players and swimmers. In addition, this combination of actions occurs when you do lateral
arm raises to shoulder level with the arm medially rotated (thumb down).
impingement: Shoulder pain caused by connective tissue (a tendon) rubbing on a
shoulder blade.
Some people believe that the impingement syndrome is a rotator cuff impingement, but
the long head of the biceps can also become impinged. Most authorities agree that
inflammation occurs from the squeezing of the supraspinatus tendon, which passes
over the head of the humerus. Therefore, beware of doing lateral arm raises only to the
level position. It may be a contributing cause to shoulder impingement, especially when
done vigorously. It also limits your shoulder joint flexibility.
SHOULDER GIRDLE
The shoulder girdle is made up of the clavicle and the scapula. However, all movements of
the scapula are usually considered movements of the shoulder girdle. They include
elevation, depression, upward rotation, downward rotation, protraction (abduction), and
retraction (adduction).
Because the shoulder is designed for mobility, its stability is reduced. The muscular
arrangements of the shoulder girdle and the shoulder joint are such that they provide the
stability that is lacking as a result of the weak arrangements of the bones and ligaments.
However, the muscles must be strong enough to provide the necessary stability. A lack of
upper-body strength accounts for many of the injuries in the shoulder region.
Injury to the ligaments and muscles of the shoulder girdle is possible if the stabilizing
components of the muscles are not strong enough to hold the joint together. Also, since
the shoulder girdle is fairly mobile relative to the trunk, in many instances it must be a
stable base against which the muscles of the shoulder joint pull. During forceful overarm
motions, the strength of the agonist and antagonist muscles surrounding the shoulder
girdle prevents overuse strains on the surrounding tissues.
In most activities involving the upper extremity, the shoulder girdle is responsible for the
initiation of the movements. For example, elevation of the scapula initiates lifting the arm;
depression precedes pulling the arm downward; protraction occurs before reaching,
throwing, or pushing forward; retraction initiates pulling backward; upward rotation takes
place for increasing the range of overhead reaching; and downward rotation allows for
forceful arm adduction at the shoulder joint.
Relationship Between the Shoulder Joint and the
Shoulder Girdle
The shoulder joint muscles are responsible for moving the arm while the shoulder girdle
muscles (which work in synchronization with the shoulder joint muscles) are responsible
for moving the scapula (and clavicle). The muscles work closely with one another to ensure
smooth, full ROM in the shoulder joint.
In bodybuilding, the muscles of the back, shoulder, and chest are usually trained
separately. However, it is
Figure 7.7 Muscles of the shoulder girdle
impossible to isolate the muscles of the back, chest or shoulder. For example, execution of
the military press involves the clavicular pectoralis major of the chest, anterior deltoid of
the shoulder, and the trapezius and serratus anterior muscles of the shoulder girdle. All of
these muscles are prime movers for their actions. Thus, the military press strongly
involves chest, shoulder, and back muscles.
To truly understand the muscle mechanics in a particular exercise, you must learn how all
the muscles work together in concert rather than think about individual body parts in
isolation. In this way, you not only get a better understanding of how the exercise is
executed, which muscles play a major role, and how they can be best developed, you learn
how to prevent injury to the shoulder joint.
For example, when doing lateral arm raises, it is commonly believed that the arms should
only be raised to the level position because if you went above the level position, only the
trapezius (or some other muscle) is involved and the deltoid would no longer be active. In
reality, it is just the opposite. The deltoid is strongest from the level position to 180° (when
the arms are overhead) and the trapezius works through the full ROM of the arm (0 to 180
degrees). Keep in mind that the shoulder girdle muscles can only move the scapulae, and
shoulder joint muscles can only move the arm; they work together in all arm movements.
Without coordinated movement of the scapula and arm, it would be impossible to move
the arm through an appreciable ROM. Also, you will have great difficulty in moving the
arm comfortably and safely.
Before going into how the muscles are involved in moving the scapula and arm, it is
important to understand the functioning of the trapezius muscle of the upper back. This
very important muscle has four sections (see Figure 7.8), each of which has a separate
action. Yet they work together in most movements. For example, the very uppermost
portion of the trapezius (Part I) is involved in scapular elevation, as seen in the shrug
exercise.
Directly below this section (Part II) some of the trapezius muscle fibers are fairly vertical,
some are horizontal, and some are in between. The more vertical fibers are involved in
elevation of the scapula, while the more horizontal fibers are involved in upward rotation
of the scapula. To produce rotation (around an axis in the middle of the scapula), the
horizontal and partially horizontal fibers pull the upper part of the trapezius in toward the
spine.
Part IV of the trapezius, the very lowermost portion of the muscle where the fibers are
almost vertical, works together with Part II to pull down on the inner border of the scapula
to rotate the scapula upward. In addition, the serratus anterior, which is located under the
armpits and attaches to the outer border of the scapula, pulls the lower outer border to
also rotate the scapula upward. These three muscles pulling on different parts of the
scapula produce the upward rotation needed whenever you raise the arm upward, either
sideways or in front, such as when doing lateral or front arm raises and the overhead
press.
Figure 7.8 Four parts of the trapezius
Part III, the middle part of the trapezius, is involved in adduction of the scapula—
movement in which the scapula moves inward toward the spine. Parts II and IV assist in
this action, which is also indicative of the importance of this movement. In addition, the
rhomboid muscle—which is located directly underneath the trapezius—is also involved in
adduction of the scapula.
Part IV of the trapezius is also a prime mover for depression in which the scapula moves
directly downward. This is the opposite of elevation, which is performed by Part I.
Depression of the scapula is very important for initiating all downward movements of the
arm from an overhead position. For example, when you are doing the pull-up or chin-up,
the scapula must be pulled down before the arm can start coming down. Also involved in
depression of the scapula is the pectoralis minor, located on the chest beneath the
pectoralis major.
The pectoralis minor and rhomboid have another major action, which is opposite that of
the trapezius—downward rotation of the scapula. Thus it is possible to see how some of the
muscles work together as prime movers, yet they may have another directly opposite
action. This relationship is beneficial for controlling movement of the scapula. For
example, the serratus anterior is a prime mover for upward rotation and abduction of the
scapula. It works together with the trapezius in scapular upward rotation but against it in
abduction since the middle trapezius is a powerful adductor.
ELBOW
The elbow joint is made up of the ends of the humerus and ulna bones. Because the radius
also articulates with the humerus, it can also be considered part of the elbow. The annular
ligament, which encircles the head of the radius and attaches to the ulna, allows the radius
to rotate around the ulna on a longitudinal axis of the forearm to provide for pronation
and supination. The only movements possible at the elbow joint are flexion and extension.
The anterior muscles are the main elbow joint flexors (biceps, brachialis, brachioradialis,
and pronator teres), which are arranged mechanically around the elbow joint. Other
anterior muscles such as the wrist flexors and extensors pass over the elbow to insert on
the humerus. The lines of force of the wrist flexor (and extensor) muscles pass so close to
the elbow joint that their function at the elbow is mainly stabilizing.
The muscular stability of the elbow is considered strong due to the number of muscles that
act as stabilizers on the anterior side. Positions in which the muscles have dislocating
components (when they are at greater than 90 degrees of flexion) occur when the muscles
are so shortened that the tension is minimal. The main elbow flexors have stabilizing and
rotary functions.
The biceps is most often considered a two-joint muscle. However, it acts on three joints
(shoulder, elbow, radioulnar) and should be strengthened in all of these actions. This
includes shoulder joint flexion with the elbow extended, elbow flexion with the shoulder
joint held in extension, and supination with the elbow bent at a 90-degree angle.
The bony arrangement and muscular stability of the posterior elbow result in a strong
posterior elbow. The main muscle on the backside of the elbow is the triceps. From its
attachment on the olecranon process of the ulna, it covers the length of the humerus.
Because of the structure of the posterior elbow, the triceps helps to stabilize the elbow
when it pulls at an angle greater than 90 degrees to the long axis of the ulna. The triceps is
a first-class lever when it pulls at a 90-degree angle to the long axis of the ulna. In this
position, 100 percent of its effort goes to the rotary function.
Because the triceps is a two-jointed muscle, the long head of the triceps lengthens at the
shoulder when shoulder flexion takes place and simultaneously shortens at the elbow end
(elbow extension) to allow a full ROM at the shoulder. This is good for economy but not
maximum strength. To fully strengthen all three heads of the triceps, you should do
resistance exercises in which you extend the shoulder joint with the elbow extended and
extend the elbow with the shoulder joint flexed. An exercise in which you extend the
shoulder joint with the elbow extended is the two-part triceps kickback. The lying 45
degrees elbow extension exercise is an example of elbow extension with the shoulder joint
flexed.
Figure 7.9 Muscles of the elbow
RELATIONSHIP BETWEEN THE SHOULDER AND
THE ELBOW
The actions of the triceps and biceps muscles at the shoulder joint are secondary to those
at the elbow joint. Because of their attachment to the scapula, when doing elbow flexion or
extension exercises, the muscles of the shoulder joint must contract in order to stabilize
the shoulder and arm. If not, the muscles will have a tendency to perform their actions at
both the elbow and shoulder joints. A multitude of muscles come into play both for
shoulder stability and to allow for a well-executed movement at the elbow joint.
The two heads of the biceps cross the shoulder joint to attach on the scapula. However,
their action at the shoulder joint is relatively weak and they come into play only when the
resistance is sufficiently great. At this time, they act mainly as secondary movers and help
stabilize the shoulder joint. Since only the long head of the triceps crosses the shoulder
joint, it plays a role as a stabilizer and, even more importantly, as a prime mover for
shoulder joint extension. Thus, it plays a key role not only at the shoulder but also at the
elbow. The rotator cuff muscles handle most of the stabilization work on the posterior
shoulder.
FOREARM
RADIOULNAR JOINT
The radioulnar joint is a combination of three joints located at the wrist, elbow, and in
between the ulna and radius bones. These joints are not very stable and the surrounding
ligaments provide the needed support. The interosseous membrane, which is located
between the shafts of the radius and ulna along their entire length, makes up the middle
joint. This membrane helps to prevent the ulna and radius from sliding past each other.
Because the muscles are also attached to the interosseous membrane, it acts to transfer
stress from the radius and ulna.
The movements of the radioulnar joint consist of pronation and supination. At the elbow,
the radius rotates around the annular ligament and does not change positions relative to
the ulna. At the wrists, when the forearm is in pronation, the radius crosses over the ulna
so that it is then on the inner side of the ulna. When the forearm is in supination, the
radius is on the lateral side of the ulna.
The muscles of the radioulnar joint act as stabilizers and produce either pronation or
supination. These muscles include the biceps, supinator, pronator teres, and pronator
Figure 7.10 Muscles that perform supination and pronation
Figure 7.11 Muscles of the forearm
quadratus. The pronator quadratus and the supinator are situated so that they pull from
the ulna on the radius to produce pronation and supination respectively. The pronator
teres has a stabilizing component but also pulls across the elbow and is thus involved in
elbow flexion when the resistance is great. It also counteracts the pull of the biceps for
supination when performing elbow flexion.
The attachment of the biceps on the medial side of the radius allows the biceps to produce
supination when the forearm is in pronation. When the forearm is pronated, the tendon of
the biceps is wrapped around the radius. This positioning causes the biceps to be weak in
elbow flexion. This is why a pull-up is easier to perform when the forearm is supinated.
A similar situation occurs with the brachioradialis. Its attachments on the inner side of the
humerus and outer side of the radius make it a pronator to the neutral position. When the
forearm is pronated, the biceps and the brachioradialis work together in supination. The
brachialis plays no role in radioulnar movements because it is attached to the ulna. This
particular arrangement of the elbow flexors must be taken into account when analyzing
elbow flexion exercises such as pull-ups (forearm in pronation), chin-ups (forearm in
supination), neutral grip pull-ups, and others.
WRIST
The wrist joint consists of the ends of the radius and ulna bones of the forearm with the
carpal bones of the hand. The movements of the wrist joint include flexion and
extension/hyperextension, radial and ulna flexion (abduction), and adduction,
respectively. Although the bony stability of the wrist is weak, it has fairly strong ligaments
to supply stability. Many muscle tendons cross the wrist on all sides to provide additional
stability, especially if they are strong.
MUSCLES OF THE WRIST JOINT
The major flexors of the wrist are the flexor carpi radialis, flexor carpi ulnaris, and the
palmaris longus. These muscles are located on the front of the forearm (i.e., on the palm
side of the hand). The major extensor muscles of the wrist include the extensor carpi
radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris. They are located
on the back of the forearm (i.e., on the back-of-the-hand side of the forearm).
The main muscles involved in wrist abduction (radial flexion) include the flexor carpi
radialis and extensor carpi radialis longus and brevis. In ulnar flexion (wrist adduction),
the flexor carpi ulnaris and the extensor carpi ulnaris are the major muscles involved. Note
how both the flexor and extensor muscles participate in the lateral movements of the
hand.
The wrist flexors and some of the finger flexors have dual functions. Their muscle mass is
located within the forearm and their tendons cross the wrist joint to attach on the bones of
the hand. When the muscles contract and shorten, the tendons also shorten, producing an
action in the wrist.
Relationship Between the Wrist Muscles and the Elbow
The elbow and wrist are connected through the wrist flexor and extensor muscles. These
muscles cross the wrist and elbow joints (from their attachment on the hand to their
attachment on the humerus). Because of this relationship, they have a role at the elbow as
well as the wrist, although they are primarily wrist muscles. The reason for this is their
major function is at the wrist.
At the elbow joint, the muscles are relatively weak and their angle of pull is more into the
joint rather than in moving the forearm. Thus, their function is to act more as stabilizers
when you execute elbow joint exercises. The forces created by the wrist extensors are also
directed into the joint. Therefore, they act similarly to the wrist flexors at the elbow.
The elbow joint is used in most all upper-body exercises and movements. A common
injury is tendinitis felt on the back of the elbow. While most think it is their elbow hurting,
it is in reality the tendons from their hands, due to poor grip. Most people assume that this
is their triceps tendon in their elbow. Most likely, it is the tendon from the wrist flexor
muscles. This set of muscles originates from the rear side of the elbow (medial epicondyle
of the humerus) and inserts onto the fingers in different arrangements. During lying
triceps extensions (skull crushers), some trainees will allow the wrist to be bent backward.
This wrist extension will cause stress and chronic pain to the backside of the elbow. You
can fix it by maintaining a strong grip on the bar and keeping the wrist flexed or stiff.
Remember to keep a firm and correct grip on the bar.
CONCLUSION
When you understand muscle mechanics, you can look at specific exercises and more
clearly see exactly how muscles function together and how some biomechanical principles
apply during those exercises. A strong comprehension of the proper biomechanics and
kinesiology of the major muscles involved in resistance training exercises will help you to
successfully select appropriate exercises that will optimize the muscle potential for
yourself, your clients, and your loved ones.
Key Terms
antigravity muscles
chondromalacia
hyperextension
impingement
two-joint-muscle
Unit Summary
I. The most accurate way to determine the key actions and muscles involved in a strength
exercise is to biomechanically and kinesiologically analyze the movements.
A. The ends of the femur and tibia bones make up the knee joint.
1. The muscles of the knee joint are predominantly two-joint muscles, including the
hamstrings, rectus femoris of the quadriceps group, gracilis, sartorius, and the tensor
fasciae latae muscles. The gastrocnemius is another two-joint muscle of the knee, which
also crosses the ankle joint.
a. The gastrocnemius, the major muscle of the posterior shin, functions to extend the foot
(plantar flexion). It ties in with the hamstrings at the knee joint where they are both
involved in knee joint flexion. In addition, the insertion of the gastrocnemius on the femur
helps to provide greater stability.
b. The muscle mass of the quadriceps is much greater than that of the hamstrings. The
quadriceps should always be stronger than the hamstrings in almost all instances because
their workload is much greater.
B. The ankle joint is made up of the tibia and talus bones.
1. The gastrocnemius is the major ankle extensor muscle of the shin. The soleus has
similar functions to the gastrocnemius. The tibialis anterior is the main muscle on the
anterior side of the shin.
C. The spine (vertebral column) is the most important functional unit of the body. It
provides the main framework and foundation for most of the movements of the body and
extremities.
1. The abdominal musculature (rectus abdominis, internal and external obliques,
transverse abdominis) acts to prevent the vertebral column from being continually
hyperextended.
a. The abdominal muscles (rectus abdominis, external and internal obliques) and the hip
flexors (iliopsoas, pectineus, and rectus femoris) work together to create maximum ROM
in your ability to raise the legs as high as possible.
D. The bony arrangement of the shoulder joint consists of a shallow socket (glenoid fossa)
into which the spherical head of the humerus fits.
1. The muscles that serve as the primary movers of the arm at the shoulder joint are the
deltoid, coracobrachialis, pectoralis major, latissimus dorsi and teres major, the long and
short heads of the biceps, and the long head of the triceps on the posterior side. The
muscles located on the front of the chest and shoulder are involved mainly in flexion and
horizontal adduction, while those on the posterior side are involved mainly in extension
and horizontal abduction.
2. The shoulder girdle is made up of the clavicle and scapula. All movements of the scapula
are usually considered movements of the shoulder girdle. These movements include
elevation, depression, upward rotation, downward rotation, protraction (abduction), and
retraction (adduction).
a. The shoulder joint muscles are responsible for moving the arm while the shoulder girdle
muscles (which work in synchronization with the shoulder joint muscles) are responsible
for moving the scapula (and clavicle). The muscles work closely with one another to ensure
smooth, full ROM in the shoulder joint.
E. The ends of the humerus and ulna bones make up the elbow joint.
1. The anterior muscles of the elbow joint are the biceps, brachialis, brachioradialis, and
pronator teres. The posterior muscles on the backside of the elbow are the triceps and
anconeus.
a. The actions of the triceps and biceps muscles at the shoulder joint are secondary to
those at the elbow joint. Because of their attachment to the scapula, when doing elbow
flexion or extension exercises, the muscles of the shoulder joint must contract to hold the
shoulder and arm in place to be stabilized.
F. The radioulnar joint is a combination of three joints located at the wrist, elbow, and in
between the ulna and radius bones.
1. The muscles of the radioulnar joint act as stabilizers and produce either pronation or
supination. These muscles include the biceps, supinator, pronator teres, and pronator
quadratus.
G. The ends of the radius and ulna bones of the forearm, with the carpal bones of the hand,
make up the wrist joint.
1. The major flexors of the wrist are the flexor carpi radialis, flexor carpi ulnaris, and
palmaris longus, which are involved in wrist flexion, extension/hyperextension, and radial
and ulnar flexion (abduction) and adduction, respectively.
a. The elbow and wrist are tied in through the wrist flexor and extensor muscles and have a
role at the elbow as well as the wrist. Although they are primarily wrist muscles, the
muscles at the elbow joint are relatively weak and their angle of pull is more into the joint
rather than in moving the forearm. Thus, their function is to act more as stabilizers when
you execute elbow joint exercises.
SECTION THREE
Health and Physical Fitness
Strength
Cardiovascular Training
Flexibility Training
Body Composition
INTRODUCTION
Several studies have explored the relationship between physical activity and the overall
quality of life (Sheppard 1996), which includes variables such as social, mental, and
psychological well-being. Physical activity plays an essential role in quality of life. It
increases energy; it promotes physical, mental, and psychological well-being; and it serves
as preventive medicine, reducing the risk of developing premature health problems. These
are just some of the compelling reasons to promote health and physical fitness.
The Surgeon General’s Report on Physical Activity and Health (USDDHS 1996) reviews
the evidence relating physical activity to reduced risks of a variety of health problems.
Evidence shows that physical activity is related to a lower risk of the premature
development of many health problems, such as anxiety, atherosclerosis, back pain, cancer,
chronic lung disease, coronary heart disease, diabetes, obesity, hypertension, and
osteoporosis. Many of these topics will be covered in Section 6 of the text. Preventing or
delaying the premature development of the aforementioned health problems also means
improving quality of life.
COMPONENTS OF TOTAL FITNESS
Total fitness means striving for the highest quality of existence, including mental,
psychological, and physical components. Total fitness involves an integrated approach that
is dynamic, multidimensional, and also relates to heredity, environmental factors, and
other components described here:
Heredity: Even though heredity influences physical fitness and health, everyone can lead
a healthy or unhealthy life regardless of genetic makeup. It is not possible to establish the
relative portion of an individual’s health or fitness that is determined through heredity.
Therefore, genetic background neither dooms nor guarantees success in achieving total
fitness.
Environment: Environment includes physical factors such as climate, altitude, and
pollution, as well as social factors such as friends, parental values, and workplace
characteristics that affect fitness and health. Past and present environments affect
everyone. For example, some children do not have adequate food as part of their
surroundings and therefore cannot focus on other components of fitness until basic needs
are met.
Freedom from Disease or Injury: Years of living in a toxic environment, poor eating
habits, inactivity, and the myriad complications that result from these situations can cause
or exacerbate otherwise preventable disease and injury. One can certainly not consider
himself or herself totally fit if disease or injury is present. Think of the word “disease”
as dis-ease, or the absence of ease. Not so coincidentally, clients who are happy and at
ease are also generally more healthy and fit.
Personal Interest: One of the major components of fitness involves personal choices,
such as time spent in the sun, smoking, drinking, arguing, and worrying. Everything from
wrinkles to osteoporosis, from arthritis to atherosclerosis, and from dental care to
dermatosis, are signs of premature aging. Most are preventable to a far larger extent than
thought possible. Over a lifetime, people who cast caution to the wind in regards to health
and fitness practices suffer higher levels of disease compared with those who have lived a
fitness lifestyle.
Freedom from Stress: Many psychologists say that stress should be measured by how
well you are able to control outcomes in your life. For example, a busy corporate president
with a majority share of ownership is less likely to succumb to the physiological ravages of
stress than a much-scrutinized football trainer.
Mind–Body–Spirit Link: The YMCA adopted a symbol of a triangle (in which the
points of that triangle symbolized mind, body, and spirit) from Native American culture.
All religions in one way or another recognize the importance of this link. Will it help you
run faster? Fight through a tackle? Concentrate on a free throw? Well, miraculous things
have happened! However, any client who does not focus on his or her overall happiness
with life will not realize his or her full potential. Because this is true, this component of
total fitness is the most important of all!
It is difficult to separate health- and performance-related physical fitness. Certainly, they
overlap. For simplicity, health-related fitness components include cardiovascular
endurance, strength, flexibility, and body composition. Performance-related fitness
includes all of the above along with power, agility, speed, and balance. As a future ISSA
personal trainer, you should understand each fitness component with special attention
given to the components of strength, cardiovascular fitness, flexibility, and body
composition. The following units focus on these four components of physical fitness and
training.