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Frederick C. Hatfield, PhD


Frederick C. Hatfield, PhD

Sal Arria, DC, MSS

Patrick S. Gamboa, MBA, MSS

Josh Bryant, MS, MFS

Paul O. Davis, PhD, FASCM

Michael Yessis, PhD

James A. Peterson, PhD

Charles Staley, BS, MSS

John Berardi, PhD

Brian St. Pierre, MS, RD

Ryan Andrews, MS, MA, RD

Karl Knopf, EdD

Thomas D. Fahey, EdD

Darin Rell, BS, CFT, AHA, BLS Instructor


Cameron Baker, BS, MFS

Josh Bryant, MS, MFS


Peter A. Balaskas

Joanna Hatzopoulos

Graphics and Illustration

Sarah McDonough, Art Director

Karen Williams, Senior Artist, Illustrator

Alex Gundersen, Illustrator

Samantha Hird, Photography (Flexibility)

Fitness: The Complete Guide (Edition 9.0)

Official course text for: International Sports Sciences Association’s Certified Fitness Trainer Course

10 9 8 7 6 5 4 3 2 1

Copyright © 2015 TXu1-157-866 International Sports Sciences Association.

Published by the International Sports Sciences Association, Carpinteria, CA 93013.

All rights reserved. No part of this work may be reproduced or transmitted in any form or by any electronic, mechanical, or other means, now

known or hereafter invented, including xerography, photocopying, and recording, or in any information storage and retrieval system without

the written permission of the publisher.

Direct copyright, permissions, reproduction, and publishing inquiries to:

International Sports Sciences Association, 1015 Mark Avenue, Carpinteria, CA 93013

1.800.892.4772 • 1.805.745.8111 (local) • 1.805.745.8119 (fax)


This text is informational only. The data and information contained herein are based upon information from various published and

unpublished sources that represents training, health, and nutrition literature and practice summarized by the author and publisher.

The publisher of this text makes no warranties, expressed or implied, regarding the currency, completeness, or scientific accuracy of

this information, nor does it warrant the fitness of the information for any particular purpose. The information is not intended for use

in connection with the sale of any product. Any claims or presentations regarding any specific products or brand names are strictly the

responsibility of the product owners or manufacturers. This summary of information from unpublished sources, books, research journals,

and articles is not intended to replace the advice or attention of health care professionals. It is not intended to direct their behavior or

replace their independent professional judgment. If you have a problem or concern with your health, or before you embark on any health,

fitness, or sports training programs, seek clearance and guidance from a qualified health care professional.


Frederick C. Hatfield, PhD

Sal Arria, DC, MSS

Patrick S. Gamboa, MBA, MSS

Josh Bryant, MS, MFS

Paul O. Davis, PhD, FASCM

Michael Yessis, PhD

James A. Peterson, PhD

Charles Staley, BS, MSS

John Berardi, PhD

Brian St. Pierre, MS, RD

Ryan Andrews, MS, MA, RD

Karl Knopf, EdD

Thomas D. Fahey, EdD

Darin Rell, BS, CFT, AHA, BLS Instructor


Cameron Baker, BS, MFS

Josh Bryant, MS, MFS


Peter A. Balaskas

Joanna Hatzopoulos

Graphics and Illustration

Sarah McDonough, Art Director

Karen Williams, Senior Artist, Illustrator

Alex Gundersen, Illustrator

Samantha Hird, Photography (Flexibility)

Fitness: The Complete Guide (Edition 9.0)

Official course text for: International Sports Sciences Association’s Certified Fitness Trainer Course

10 9 8 7 6 5 4 3 2 1

Copyright © 2015 TXu1-157-866 International Sports Sciences Association.

Published by the International Sports Sciences Association, Carpinteria, CA 93013.

All rights reserved. No part of this work may be reproduced or transmitted in any form or by any electronic, mechanical, or other means, now

known or hereafter invented, including xerography, photocopying, and recording, or in any information storage and retrieval system without

the written permission of the publisher.

Direct copyright, permissions, reproduction, and publishing inquiries to:

International Sports Sciences Association, 1015 Mark Avenue, Carpinteria, CA 93013

1.800.892.4772 • 1.805.745.8111 (local) • 1.805.745.8119 (fax)


This text is informational only. The data and information contained herein are based upon information from various published and

unpublished sources that represents training, health, and nutrition literature and practice summarized by the author and publisher.

The publisher of this text makes no warranties, expressed or implied, regarding the currency, completeness, or scientific accuracy of

this information, nor does it warrant the fitness of the information for any particular purpose. The information is not intended for use

in connection with the sale of any product. Any claims or presentations regarding any specific products or brand names are strictly the

responsibility of the product owners or manufacturers. This summary of information from unpublished sources, books, research journals,

and articles is not intended to replace the advice or attention of health care professionals. It is not intended to direct their behavior or

replace their independent professional judgment. If you have a problem or concern with your health, or before you embark on any health,

fitness, or sports training programs, seek clearance and guidance from a qualified health care professional.

About the Author | iii


Frederick C. Hatfield, MSS, PhD, is co-ounder and

president o the ISSA. Dr. Hatfield, (aka “Dr. Squat”)

won the World Championship three times in the

sport o powerlifing and perormed a competitive

squat with 1014 pounds at a body weight o 255

pounds (more weight than anyone in history had

ever lifed in competition). Dr. Hatfield’s ormer

positions include an assistant proessorship at the

University o Wisconsin (Madison) and senior vice

president and director o research and development

or Weider Health and Fitness, Incorporated. Dr.

Hatfield was honored by Southern Connecticut State University when they presented

him with the 1991 Alumni Citation Award. He has written over 60 books (including

several best-sellers) and hundreds o articles in the general areas o sports training, ing,

fitness, bodybuilding, and perormance nutrition. He has been coach a nd training

consultant or several world-ranked and proessional athletes, sports governing

bodies, and proessional teams worldwide. Dr. Hatfield qualified or the 1998 World

Championships in Olympic Lifing and competed in the Masters Division.

International Sports Sciences Association


Introduction, p. 1



1 Metabolism, p. 11

2 Basic Anatomy and Physiology, p. 29

3 Musculoskeletal Anatomy

and Physiology, p. 71



4 Kinesiology of Exercise, p. 115

5 Biomechanics of Exercise, p. 131

6 Musculoskeletal Deviations, p. 149

7 Muscle Mechanics, p. 161



8 Strength, p. 183

9 Cardiovascular Training, p. 301

10 Flexibility Training, p. 333

11 Body Composition, p. 359



12 Drawing-In Phase, p. 383

13 Basic Assessment of

Fitness Participants, p. 393

14 Training Principles, p. 415

15 Periodization, p. 459

16 Determining Training Loads, p. 477



17 The Big Picture of Nutrition, p. 497

18 Nutritional Physiology, p. 517

19 Nutritional Science, p. 545

20 Nutritional Coaching, p. 575



Topics in Fitness for Special Populations , p. 615

21 Exercise and Older Adults, p. 617

22 Exercise and Adaptive Fitness, p. 627

23 Exercise and Our Youth, p. 635

24 Exercise and Hypertension, p. 641

25 Exercise and Diabetes, p. 647

26 Exercise and Arthritis, p. 653

27 Exercise and Coronary

Heart Disease, p. 659

28 Exercise and Pregnancy, p. 665

29 Exercise and Asthma, p. 671

30 Sports Medicine

in the Trenches, p. 677

31 Basic First Aid, p. 715

References, p. 725

Glossary, p. 737

Index, p. 759


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




2 | Introduction

U.S. President Theodore Roosevelt


oday’s fitness industry is a multibillion-dollar business.

Personal training is its ever-growing offspring. Te roots

o 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 o recorded

history. While the proession and terminology associated

with personal training were not yet in existence, the

concept o optimal health (which is the motivation behind

the proession) 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.”

O all o the leaders o the United States, Teodore

Roosevelt was one o the strongest presidents, both

physically and mentally. However, he did not start that

way. As a child, Roosevelt was small or his age and quite

sickly. He had debilitating asthma, had poor eyesight, and

was extremely thin. When he was 12 years old, his ather

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: Teodore

Roosevelt’s strength in mind and body contributed to his

strength as the leader o his nation.

Another great leader was U.S. President John Kennedy.

Like Roosevelt, Kennedy acknowledged the benefits o

physical activity or 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.”

Fitness: The Complete Guide

The Who, What, Why, and How of Personal Training | 3



According to the International Health, Racquet & Sports

Club Association and American Sports Data (IHRSA/

ASD) Health Club rend Report, since 1998, the number

o Americans belonging to health clubs has grown

45 percent (about 14 million members). Health club

memberships among children under 18 years o age have

jumped by 187 percent since 1987. Te number o 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 o health clubs. Over 12 percent o

these members pay or the services o a personal trainer

and over 6 million health club members alone paid or

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:

• 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:


1–6 47%

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

6–11 22

12–17 26

18–34 15

35–54 14

55 + 24


Tese statistics support the growing trend and need or

personal training services. While those 4 million people

who purchased personal training services are sold on the

need or personal training, let’s explore what exactly is a

personal trainer?



Te proession o personal training is a relatively new

field that continues to expand its boundaries and redefine

itsel. Prior to the early 1980s, no minimal requirements

existed to qualiy or identiy a person as a personal

trainer. Tose engaged in training were still an esoteric

group. Many learned about training solely through

personal experiences in the gym. Recognizing the need

or standardization and credibility, Dr. Sal Arria and Dr.

Fred Hatfield pioneered a program o personal fitness

training that merged gym experience with practical and

applied sciences.

oday, a personal fitness trainer can be defined as a person

who educates and trains clients in the perormance o sae

and appropriate exercises in order to effectively lead them

to optimal health. Personal trainers can be sel-employed

or work in health clubs, physicians’ offices, physical

therapy clinics, wellness centers, hospitals, rehabilitation

acilities, and private studios.



Te U.S. Surgeon General’s Report on Physical Activity

and Health supports the role o physical activity or

good health and disease prevention. Te National

Institutes o Health released a consensus statement on the

importance o physical activity or cardiovascular health

(US Department o Health and Human Services,). In

addition, the Centers or Disease Control and Prevention

(CDC) launched the Healthy People Initiative, which

lists physical activity, fitness, and nutrition at the top o

twenty-two priority areas. Finally, the American Heart

Association included physical inactivity and low fitness

levels as primary risk actors, along with smoking,

hypertension, and high cholesterol.

Unortunately, although the resounding benefits o

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 o people remain

sedentary. o make matters worse, ederal resources

and unds or physical activity have lagged ar behind

other aspects o 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 ofen the first to be cut.

International Sports Sciences Association

4 | Introduction

Consider the ollowing: Each year in the United States,

people spend $2.5 trillion on health care. Tis meteoric

figure translates into an expenditure o almost $7,000 or

each member o the U.S. population. Regrettably, this

financial commitment has neither shown signs o abating

nor has it produced satisactory results with regard to

treating a wide variety o chronic health problems.

Attempts to identiy the actors that have been major

contributions to this virtual epidemic o medical

problems have produced a litany o probable reasons

why such a large number o individuals are so apparently

unhealthy, including poor eating habits, sedentary

liestyle, stress, and poor health habits (e.g., smoking). At

the same time, a number o studies have been undertaken

to identiy what, i anything, can be done to diminish

either the number or the severity o medical problems

affecting the public. Tese studies have provided

considerable evidence that exercise has substantial

medicinal benefits or people o all ages.

wo o the most widely publicized efforts to investigate

the possible relationship between exercise and disease

were longitudinal studies, each o which involved more

than 10,000 subjects. In a renowned study o 17,000

Harvard graduates, Ralph Paffenbarger, MD, ound that

men who expended approximately 300 calories a day (the

equivalent o walking briskly or 45 minutes) reduced

their death rates rom all causes by an extraordinary 28

percent and lived an average o more than 2 years longer

than their sedentary classmates. Another study conducted

by Steven Blair, PED, o the Institute o Aerobics

Research in Dallas documented the act that a relatively

modest amount o exercise has a significant effect on

the mortality rate o both men and women. Te higher

the fitness level, the lower the death rate (afer the data

were adjusted or age differences between subjects in this

8-year investigation o 13,344 individuals). An analysis

o 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 o medical problems

and in decreasing your ultimate costs or health care is

critical. Despite the vast number o individuals who lead a

sedentary liestyle, the need or and the value o exercising

on a regular basis is an irreutable act o lie (and death).

For example, afer a detailed review o the results o his

long-term investigation, Dr. Paffenbarger concluded that

not exercising had the equivalent impact on a person’s

health as smoking one and a hal packs o cigarettes a

day. Fortunately, with ew exceptions, most people are too

sensible to ever consider ravaging their health by smoking

excessively. Unortunately, many o these same people ail

to recognize the extraordinary benefits o exercise in the

prevention o medical problems.

Any listing o 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 o these health concerns and the

manner in which exercise is thought to help alleviate each

condition are the ollowing:

• 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.

• Cholesterol. Exercise helps to raise HDL (highdensity

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.

Fitness: The Complete Guide

The Who, What, Why, and How of Personal Training | 5

• Diabetes. Exercise helps lower blood sugar

levels, strengthen the skeletal muscles and heart,

improve circulation, and reduce stress.

• Fatigue. Exercise can help alleviate the fatiguecausing

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


• 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.

• 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


• 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.

International Sports Sciences Association

6 | Introduction

Are the positive effects that result rom exercising

regularly worth the required effort? Absolutely. Should

you make exercise an integral part o your daily regimen?

O course, you should. In countless ways, your lie may

depend on it. Te meteoric rise o health care and

health problems makes your success as a personal

trainer predictable.

Implications for Certified Fitness

Trainer Professionals

Te need or personal training services continues to grow.

As uture ISSA fitness proessionals, it is imperative that

we keep up with the evolving recommendations or health

and physical fitness that have a direct application or

fitness programs and exercise recommendations. With

the emergence o the latest technologies, inormation

regarding health and fitness is easily accessible. However,

because o the nature o the media’s use o vague and

brie headlines in conjunction with radio and television

sound bites that provide only limited, conusing, and

ofen conflicting recommendations, it is important that

we can help our clients, riends, and amily 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 post-rehabilitation,

corporate wellness, youth fitness, senior fitness, and preand

postnatal specializations to better serve their clients

in achieving and living the fitness liestyle. As you can see,

we as personal trainers have an inherent responsibility

to positively influence the health and fitness attitudes

o those around us. Individually and collectively, we

can bring health and fitness to the masses and make the

dream o optimal health a reality or all.



As the industry continues to expand its boundaries and

the realm o scientific knowledge concerning the human

response and adaptation to exercise continues to g row, it

is essential that personal fitness trainers be competent in

the ollowing:

• 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 proessionals to educate and

effectively draw our clients into the fitness liestyle

and optimal health comes rom a plan that is based in

the aorementioned areas as well as the knowledge o

Fitness: The Complete Guide

The Who, What, Why, and How of Personal Training | 7

muscular, cardiopulmonary, and metabolic adaptations.

Tese adaptations are known as the training effect . Te

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. Te heart and capillaries

become stronger and more dispersed in order to allow a

more efficient flow o oxygen and nutrients. Te muscles,

tendons, and bones involved with this activity also

strengthen to become more proficient. In time, the body

releases unnecessary at rom its rame, and stride and

gait become more efficient. Additionally, resting heat

rate and blood pressure drop. Tese adaptations can be

achieved through an educated trainer who can develop an

appropriate fitness and health plan.

Te fitness and health plan must account or the basic

principles o fitness training: overload, specificity,

individual differences, reversibility, periodization, rest,

overtraining, and stimulus variability. Te plan requires

a thorough understanding o the major muscles o the

body and how they work, as well as an understanding

o metabolism—how the body converts ood energy

into other orms o energy it can use at rest and during

exercise. In addition, trainers must learn about the

unction and regulation o 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 riends, amily

members, and uture clients into the fitness liestyle 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.

International Sports Sciences Association

8 | Introduction


Principles and Purposes

Upon receipt o the ISSA Certificate, members become, in effect, de acto representatives o the leader in the fitness

certification industry, and as such are expected to conduct themselves according to the highest standards o honor, ethics,

and proessional behavior at all times. Tese principles are intended to aid ISSA members in their goal to provide the

highest quality o 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


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


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


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


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.

Fitness: The Complete Guide


Anatomy and Physiology


Basic Anatomy and Physiology

Musculoskeletal Anatomy and Physiology




Understanding Metabolism

Metabolic Set Point

Food and Metabolism

Environment and Metabolism

Exercise and Metabolic Responses

Energy Metabolism

ATP Production

Monitoring Metabolism




12 | Unit 1

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:

• 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.

training effect: An increase in

functional capacity of muscles

and other bodily tissues as

a result of increased stress

(overload) placed upon them.

homeostasis: The automatic

tendency to maintain a relatively

constant internal environment.


As revealed in the book’s introduction, personal fitness trainers have a tremendous

influence on shaping the health and fitness attitudes and practices o those around

them. Te sphere o influence includes riends, amily members, coworkers, and, o

course, clients. As a fitness proessional, your ability to effectively draw your clients

into the fitness liestyle—including the ability to maintain optimal health—largely

depends on your knowledge o the muscular, cardiopulmonary, and metabolic

adaptations to exercise. Tese adaptations are known as the training effect.

Te training effect impacts the body in several ways. Te body begins to change

at the cellular level, allowing more energy to be released with less oxygen. Heart

unction improves and the capillaries prolierate in order to allow a more efficient

flow o oxygen and nutrients. Te muscles, connective tissues, and bones involved

with a particular physical activity strengthen to accommodate improved proficiency

at perorming the activity. Over time, the body’s composition changes (e.g., at 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 yoursel and learning how to develop appropriate

fitness and health plans or them.

Fitness: The Complete Guide

Metabolism | 13

Te 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 rom?

Where Does Energy Come From?

All energy on earth originates rom the sun. Plants use

the light energy rom the sun to orm carbohydrates, ats,

and proteins. Carbohydrates are sugars and starches used

by the body as uel. Fats are compounds that store energy.

Proteins are important components o cells and tissues;

they are large, complex molecules comprised o amino

acids. (Carbohydrates, ats, and proteins are discussed

in more detail in Section 5 o this text.) Humans and

other animals eat plants and other animals to obtain

energy required to maintain cellular activities. Te body

uses carbohydrates, ats, 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, ats,

and proteins into a biologically usable orm o energy

to both uel physical activity and provide the structura l

components o the body. Te ability to run, jump, and

lif weights is contingent upon, and limited by, the body’s

ability to transorm ood into biological energy. Tese

physical abilities are urther contingent upon thousands

o chemical reactions that occur throughout the body

all day long. Collectively, these reactions are known as

metabolism. Tese many chemical reactions occurring

in the body must be regulated in order to maintain a

balance. Te body consists o trillions o cells, which are

organized into tissues, organs, and systems. Tis intricate

organized system is covered in more detail in Unit 2. Te

body’s components work together in a highly organized

manner to maintain this balance. Metabolic activities are

continually occurring in the trillions o cells in your body

and must be careully regulated to maintain a constant

internal environment, or steady state. Tis steady state

must be maintained regardless o your ever-changing

external environment.


Homeostasis reers to the body’s automatic tendency

to maintain a constant internal body environment

through various processes. Walter Bradord Cannon is

credited with coining the term in his book Te Wisdom

of the Body (1932). For homeostasis to work, eedback

systems must exist that various physiological unctions

turn off and on. Imagine a eedback system such as the

thermostat in your urnace or air conditioning system. I

Room condition

warms up

Room condition

returns to normal





Figure 1.1 Homeostasis example

Room condition

returns to normal

Room condition

cools down

the temperature increases above the set point determined

by the system, then the thermostat shuts off the urnace.

In this way, the temperature is kept at the desired steady

state. I the temperature decreases below the set point

determined by the system, then the thermostat turns

on the urnace to maintain the desired steady state (see

Figure 1.1). Tis eedback system revolves around a

cycle o events. Inormation about a change is ed back

to the system so that the regulator (in this example, the

thermostat) can control the process (in the example o

temperature regulation).

A good example o homeostasis in the body is the method

by which the body maintains a constant temperature o

98.6 degrees Fahrenheit. For example, i either physical

exertion or external heat causes your body temperature

to rise, your brain sends a signal to increase the rate o

sweating. Heat is carried away in sweat, which evaporates.

I body temperature begins to drop due to a cold external

International Sports Sciences Association

14 | Unit 1

environment, shivering begins to generate heat and keep the body temperature at that

critical 98.6 degrees F. Other metabolic unctions under homeostatic control include

the ollowing:

• 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

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


glucose: Principal circulating

sugar in the blood and the

major energy source of the


ketone bodies: Bodies

produced as intermediate

products of fat metabolism.

lactic acid: A by-product

of glucose and glycogen

metabolism in anaerobic muscle


amino acid: The building

blocks of protein. There are

24 amino acids, which form

countless number of different


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).

Te concept o homeostasis is o 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. I you

spend most o your time lifing heavy weights, your muscles will grow larger; a shif

in your homeostasis takes place. Te simple action o weight training causes more

protein synthesis in the target muscles. Hormone levels change to accommodate this

growth. On the other hand, i you choose to run several miles per day, your muscles

will adapt differently. Tey develop a higher endurance capacity, they stimulate the

ormation o more at-burning, slow-twitch 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 o the wrong oods or too little o the right

oods can cause homeostasis to shif out o balance. Consume too many calories, and

your body stores at; too little protein, and your muscles break down. I you don’t

consume enough energy-supplying calories, you will eel tired sooner. For optimum

homeostasis and metabolism, eating the right nutrients in the right amounts at the

right times is vital.


Te body sustains itsel and adapts to its environment through metabolism. In order

or metabolism to occur, the body needs both energy and building blocks or growth

and repair. It gets its energy rom the breakdown o nutrients such as glucose, ketone

bodies, lactic acid, amino acids, and fatty acids. o construct molecules or growth

and repair, a delicate interplay must exist between anabolism and catabolism.

Te 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 o 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 o substances and body tissues and may lose weight.

Anabolism includes the chemical reactions that combine different biomolecules to

create larger, more complex ones. Te net result o anabolism is the creation o new

cellular material, such as enzy mes, proteins, cell membranes, new cells, and growth/

repair o the many tissues. Tat energy is stored as glycogen and/or at and in muscle

tissue. Anabolism is necessary or growth, maintenance, and repair o tissues.

Catabolism includes the chemical reactions that break down complex biomolecules

into simpler ones or energy production, or recycling o molecular components, or

or their excretion. Catabolism provides the energy needed or transmitting nerve

impulses and muscle contraction.

Fitness: The Complete Guide

Metabolism | 15

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

o oods in the gastrointestinal system. For optimal unction, a healthy metabolism

needs many nutrients. A slight deficiency o even one vitamin can slow down

metabolism and cause chaos throughout the body. Te body builds thousands o

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 unctions taking place.


Based on the discussion o homeostasis and metabolism, it is evident that the body

is a highly regulated collection o many biochemical reactions. Much research

over the years has revealed that the body seeks to maintain a cer tain base rate o

metabolism, called the metabolic set point, which results in basal metabolic

rate (BMR). Tis set point is regulated by both genetic and environmental actors.

Researchers have demonstrated that you can change your metabolic set point through

diet and physical activity.

Te 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 at easily, while people with a ast metabolism seem to be able to eat and never

gain at. Your metabolic set point can be influenced by the external environment

(climate), nutrition, exercise, and other actors. Studies have demonstrated that when

individuals go on a low-calorie diet, the body’s metabolic set point becomes lower

in order to conserve energy. It actually resets itsel to burn ewer calories, thereby

conserving energy. Exercise tends to increase metabolic rate, causing the body to burn

more at or energy.

Calculating Caloric Expenditure

You can estimate your total daily caloric expenditure by multiplying the Harris-

Benedict equations or basal metabolic rate by an activity level actor that accounts or

your daily physical activity levels and t he thermic effect o ood.

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


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.”

Calculating Caloric Expenditure

MALE metric: DCE = ALF × ((13.75 × WKG) + (5 × HC) – (6.76 × age) + 66)

imperial: DCE = ALF × ((6.25 × WP) + (12.7 × HI) – (6.76 × age) + 66)

FEMALE metric: DCE = ALF × ((9.56 × WKG) + (1.85 × HC) – (4.68 × age) + 655)

imperial: DCE = ALF × ((4.35 × WP) + (4.7 × HI) – (4.68 × age) + 655)


ALF = Activity level factor


DCE = Daily caloric expenditure Sedentary: ALF = 1.2

HC = Height in centimeters Lightly active: ALF = 1.375

HI = Height in inches Moderately active: ALF = 1.55

WKG = Weight in kilograms Very active: ALF = 1.725

WP = Weight in pounds Extremely active: ALF = 1.9

Eq. 1.1

16 | Unit 1

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 1kilocalorie


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.

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.


In addition to exercise, the type o ood you eat can also influence your metabolism.

Te ood you eat can be burned to liberate energy, it can be converted into body

weight, or it can be excreted. All oods release heat when they are burned. Tis

release o heat is measured in kilocalories. A calorie is a unit o heat. Practically

speaking, this unit is too small to be useul, thereore, the kilocalorie (1,000 calories)

is the preerred unit in metabolism studies. Te term Calorie (with a capital “C”) is

synonymous with kilocalorie.

Te heat liberated rom ood is known as the thermic effect. Increased thermogenesis

(heat production) correlates with increased oxygen consumption and an increased

metabolic rate. Te more heat your body produces, the more oxygen it needs, because

heat cannot be liberated in the absence o oxygen. Food efficiency is simply a measure

o how efficiently a particular ood is converted to body weight. Foods with high

ood efficiency are prone to be converted to body weight, while oods with low ood

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 o body at.

Te heat liberated rom a particular ood, whether it is at, protein, or carbohydrate,

is determined by its particular molecular structure, and this structure determines

its thermic effect. Te higher the thermic effect o any par ticular ood, 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 o determining the mix

o uels being utilized in the body is ca lled the respiratory quotient (RQ), which

provides a way to measure the relative amounts o ats, carbohydrates, and proteins

being burned or energy.

Te respiratory quotient (RQ) is the ratio o the volume o carbon dioxide expired

to the volume o oxygen consumed. Because the amounts o oxygen used up or the

combustion o at, carbohydrate, and protein differ, differences in the RQ indicate

which nutrient source is being predominantly used or energy purposes. Te ormula

or calculating RQ is as ollows:

RQ = volume of CO 2

expired ÷ volume of O 2


Eq. 1.2

oxidation: The chemical act

of combining with oxygen or of

removing hydrogen.

Te RQ or carbohydrate is 1.0, whereas the RQ or at is 0.7. Fat has a lower RQ value

because atty acids require more oxygen or oxidation than the amount o carbon

dioxide produced. Te RQ or energy production rom protein is about 0.8. Te

average person at rest will have an RQ o about 0.8; however, this result is rom using a

mixture o atty acids and carbohydrates, not the protein itsel, or energy production.

Remember, proteins (broken down into amino acids) are not usually used or energy.

In a normal diet containing carbohydrate, at, and protein, about 40to 45 percent o

the energy is derived rom atty acids, 40 to 45 percent rom carbohydrates, and 10 to

15 percent rom protein. However, this rate o energy production varies based on diet,

physical activity, and level o physical training.

Fitness: The Complete Guide

Metabolism | 17

Research indicates that when the diet is high in carbohydrates, the RQ is higher,

thereore more energy is being produced rom carbohydrates. When the diet is low in

carbohydrates and high in at, more energy is produced rom at. Interestingly, recent

studies published in academic journals suggest that more efficient body at reduction

occurs with a high-at diet than with a high-carbohydrate diet (on a calorie-percalorie


In addition, training intensity affects the energy source during exercise. For example,

a training intensity below 60 percent o maximal oxygen uptake ( • VO 2

max) results

in a RQ o about 0.8, indicating an equal portion o energy derived rom atty acids

and carbohydrate. As training intensity increases above 60 percent o • VO 2

max, more

carbohydrate is used or energy. Exercise intensity at 100 percent • VO 2

max (which can

only be sustained or minutes) yields a RQ o 1. Keep in mind that amino acids, in

particular the branched-chain amino acids (BCAAs, which aid in recovery), are also

being used or energy during exercise and at rest, perhaps as much as 10 percent or

more during exercise.

In general, physical conditioning lowers the RQ, which means more energy is being

obtained rom atty acids in the trained individual. However, more energy is also

being obtained rom protein in the trained individual. Carbohydrate is always being

used or energy. For example, in a study comparing the RQ o untrained versus

trained individuals during exercise, the RQ o the untrained individuals was 0.95 and

the RQ o the trained individuals was 0.9. Tis means that while both groups were

using mostly carbohydrate or uel during exercise, the trained individuals were using

a higher amount o atty acids or energy. At rest, atty 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 atty acids and carbohydrate or energy. O course, these ratios change

when one consumes only ats and proteins and no carbohydrates as uel.

While this discussion o RQ is very brie, you can see that the energy substrate

utilization o the body is quite varied, and both composition o the diet and intensity

o physical activity determine which energy substrates are used. Tereore, it is easy to

see why different sports require different dietary considerations.

maximal oxygen uptake

( • VO 2

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 long-distance events when

the body recruits protein for

as much as 20 percent of its

energy needs.

International Sports Sciences Association

18 | Unit 1



Te 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 o the

body begins to drop rom being in the cold. Shivering is

actually a series o involuntary muscle contractions that

are triggered to create heat in the body, like turning on

a urnace. When exposed to higher-than-average cold

conditions or a ew days, the body actually increases its

basal metabolic rate; its goal is to run hotter than average

in order to compensate or 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 ast. Afer several

days o acclimating to the hot climate, the metabolic rate

decreases and 80 degrees F eels as hot as the 60 degrees F

did a ew months earlier.



Exercise stimulates a series o metabolic responses

that affect the body’s anatomy, physiology, and

biochemical makeup.

Endurance exercise stimulates the following changes:

• Increased muscle glycogen storage capacity

• 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

Te magnitude o these changes is driven primarily by

whether the exercise is anaerobic or aerobic. Te type and

duration o exercise dictates the primary energy mix used.

High-intensity exercise simulates development o asttwitch

muscle fibers, while low-intensity exercise results

in development o slow-twitch muscle fibers.

In addition, a series o hormonal changes occur during

exercise and non-exercise periods. Tese changes also

are benefited and acilitated with a nutrient profile that

matches the type o metabolic fluctuation.

Aerobic System Changes

Aerobic training greatly increases the body’s unctional

capacity to transport and use oxygen and to burn atty

acids during exercise. Recent research shows that long,

slow distance training is not as efficient as interval

training in acilitating this unctional capacity. Some o

the major changes measured as a result o aerobic exercise

(especially interval training) include the ollowing:

• 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

Fitness: The Complete Guide

Metabolism | 19

Anaerobic System Changes

Anaerobic training greatly increases the body’s unctional capacity or development o

explosive strength and maximization o short-term energy systems. Some o the major

changes measured as a result o anaerobic exercise include the ollowing:

• 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)

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.

• 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


Energy metabolism is a series o chemical reactions that result in the breakdown o

oodstuffs (carbohydrate, at, 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 o energy

storage and energy systems used is related to physical activity.

Physical activities can be classified into these our basic groups, based on the energy

systems that are used to support these activities:

• 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 ew seconds or less at maximal effort, the muscles

depend on the immediate energy system, namely AP 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 o energy. AP and

CP are replenished rom energy derived rom complete breakdown o glucose, atty

acids, and some proteins.


Adenosine triphosphate (AP) is the molecule that stores energy in a orm that can

be used or muscle contractions. Energy production then revolves around rebuilding

AP molecules afer they are broken down or energy utilization. Muscle cells store a

limited amount o AP. During exercise the body requires a constant supply o AP in

International Sports Sciences Association

20 | Unit 1

order to provide the energy needed or muscular contraction. Tereore, to maintain

a constant supply o energy, metabolic pathways must exist in the cell with the ability

to produce AP rapidly. Muscle cells can produce AP by any one o or a combination

o three metabolic pathways: the AP/CP pathway, the glycolytic pathway, and the

oxidative pathway.

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/CP Energy Pathway

Creatine phosphate (CP) is high-energy phosphate molecule that is stored in cells and

can be used to immediately re-synthesize AP. Te ATP/CP pathway (see Figure 1.2)

is anaerobic, which means it requires no oxygen or energy use. Tis energy pathway is

demonstrated in sports that require ballistic, explosive strength or maximal effort or

short periods o time, such as shot putting, pitching, weight lifing, and powerlifing.

AP is the energy source or all human movement. Te release o one o its three

phosphate molecules provides the energy or human movement. Unortunately,

muscle cells store only a limited supply o AP that is readily available or use (5

mmol/kg o muscle). In maximal efforts, it is totally gone within 1.26 seconds!

However, regardless o their intensity or length, all activities begin with this pathway.

With the help o an enzyme called myosin APase, AP loses one phosphate molecule

in order to release energy (see Equation 1.3).


myosin ATPase

ADP + Pi + Energy

Eq. 1.3

Pi: inorganic phosphate

ADP + Pi is

resynthesized into


CP from muscle

lends a phosphate

(Pi) to ADP


ATP losses

phosphate to

release energy


Energy for

muscle contraction

Figure 1.2 The ATP/CP energy pathway

Fitness: The Complete Guide

Metabolism | 21

For short-term, high-intensity activities such as shot putting or throwing, this

pathway is enough. However, urther use in this pathway requires that the adenosine

diphosphate (ADP; di = the two phosphate molecules lef afer one is lost) be resynthesized

back to AP with the help o creatine phosphate (CP) and an enzyme

called creatine kinase (see Equation 1.4).

Eq. 1.4


Creatine Kinase

ATP + Creatine

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.

Like AP, CP is stored in small amounts (16 mmols/kg o muscle). As seen in Figure

1.3, CP stores all rapidly afer 10 seconds o maximal activity and are usually

completely depleted in under 60 seconds.

Whether or not you can increase your resting levels o AP 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

o fiber hypertrophy (increase in size), thus more AP can be stored in type II than in

type I muscle fibers (considering the size and growth potential o type II fibers).

Perhaps an even bigger question than “how much?” or “can you increase?” is “how

quickly can AP and CP stores be replenished?” Although individual differences exist,

research has shown that AP stores can be ully restored within 3.5 minutes and CP

stores can be ully replenished within 8 minutes.


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.
























Time in Seconds

Figure 1.3 Pathways of muscular energetics

International Sports Sciences Association

22 | Unit 1

glycolytic pathway: A

metabolic process in which

glucose is broken down to

produce energy anaerobically.

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.

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


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


beta oxidation: A series of

reactions in which fatty acids are

broken down.

Glycolytic Pathway

Like the AP/CP pathway, the glycolytic pathway is anaerobic. Once it has depleted

the readily available AP/CP stores, the body must break down carbohydrates to

produce more AP. Tis process uses either glycogen (which is stored in the muscle

cells) or glucose (which is ound in the blood) to convert ADP back into AP; the

waste product is lactic acid (see Equation 1.5).

Glucose + 2Pi + 2ADP + 2NAD +

Eq. 1.5

Tis lactic acid eventually builds more quickly than it can be flushed out o the muscle

to the point o the anaerobic threshold, otherwise known as muscular atigue. 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 orm, called lactate, which is used either as an energy

substrate or to produce more glucose (a process called gluconeogenesis). Getting

rid o lactic acid is not as important as it is how efficiently the body can use it. I you

produce lactic acid aster 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 actor; the limiting actor is the accumulation o lactic acid.

Generally, the glycolytic pathway ends under maximal conditions at around 80

seconds beore the oxidative pathway (and lower levels o activity) takes over.

How well muscles function in the glycolytic pathway is determined by three

related factors:

• 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 afer 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 or the ability to tolerate the pain, it

comes with personal experience.

Oxidative Pathway

2 lactic acid + 2ATP + 2NAD

Te oxidative pathway is a system that is aerobic, which means it uses oxygen to

produce AP by way o the Krebs cycle and electron transport chain. Ultimately,

more AP 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 AP. In the end, up to 38

molecules o AP can be produced through the oxidative pathway.

It is only in this pathway that at can be used or energy. Breaking down at or energy

is also a long process (called beta oxidation), which does not directly produce AP.

Fitness: The Complete Guide

Metabolism | 23

Rather, it provides the coenzymes needed or the Krebs

cycle. Scientists have estimated that while at rest (and in

the oxidative pathway), 70 percent o energy comes rom

at, not carbohydrates or protein. However, as exercise

intensity increases, more and more carbohydrates are

used instead o at (beta oxidation can’t keep up). In act,

at the upper limits o the aerobic pathway, 100 percent o

the energy is coming rom carbohydrates—not at! I at

these levels carbohydrates aren’t available, the body will

indeed catabolize the very muscle it’s using or energy.

How the Systems Interact

o better understand how each o 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. Te brain sends a signal

along the nerves, triggering a release o calcium ions in

the muscles, which stimulates the muscles to contract

and, in the process, the high-energy molecule AP

releases energy and is reduced to ADP plus one phosphate



Creatine phosphate

ADP + P i

Myosin ATPase





Amino acids







Lactic acid

Fatty acids





Figure 1.4 Pathway interactions

International Sports Sciences Association

24 | Unit 1

atom. In this way, the immediately available AP stores

are depleted very rapidly, in the first ew seconds o a

maximal muscle contraction.

Te second immediate source o cellular energy is creatine

phosphate (CP). Te cell contains several more times

CP molecules than AP molecules. Creatine phosphate

serves to instantaneously regenerate AP molecules.

Tereore, the AP that is broken down to ADP during

muscle contraction is restored to the high-energy AP by

CP. Te third immediate energy system enables the cell to

regenerate AP rom two ADP molecules, resulting in one

AP and one adenosine monophosphate (AMP) molecule.

Tis immediate energy source is depleted in a matter

o seconds under conditions o all-out effort (maximal

muscle contractions).

Te storage capacity o AP and CP in a cell is quickly

reached or a particular muscle size. In order to increase

the amount o AP and CP on hand, the muscle fibers

must increase in size. Tis is why power athletes get big

muscles. Te workload demands that more AP and CP be

available. o 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. Te non-oxidative system is a

major contributor o energy during 4 to 50 seconds o

effort. Non-oxidative metabolism (glycolysis) involves the

breakdown o glucose to regenerate ADP into AP. Muscle

tissue is densely packed with non-oxidative enzyme

systems. What happens chemically is that the glucose

molecule is split in hal and energy is released. Tis energy

is enough to regenerate 2 AP molecules and leave two

pyruvate molecules. In general, these pyruvate molecules

are immediately converted to lactic acid molecules. Te

amount o ree glucose is generally low in the cells, so

glucose is derived rom the breakdown o glycogen.

Fast-twitch muscle fibers (those associated with strength

and size) are also reerred to as ast glycolytic muscle

fibers, because they house the metabolic machinery to get

quick energy through ast glycolysis pathways. Te asttwitch

fibers have a low capacity or oxidative metabolism

and are instead set up to run glucose through their ast

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 rom the muscle, ed

into the bloodstream, taken to the liver, and there made

into glucose and glycogen. Glycolysis takes place in the

cytoplasm o the cell.

For physical activities lasting more than 2 minutes, the

oxidative metabolic pathways produce the majority

o energy to maintain muscle contractions. Potential

oxidative energy sources include glucose, glycogen, ats,

and amino acids. Oxidative energy production takes

place in the mitochondria o the cells. Far more energy

is produced when glucose is completely broken down

in the mitochondria. Glucose is still first split in hal

by glycolysis. Te pyruvate molecules then enter into

the mitochondria, where they are completely broken

down. Te oxidative pathways are the Krebs cycle and

electron transport. Fatty acids, which come rom at,

are a major energy source during endurance events. Te

processes o at 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.

Fitness: The Complete Guide

Metabolism | 25

Glycogen Depletion

and Metabolism of Fatigue

Glycogen is essential to perormance or 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 uel is atty acids, glycogen is also utilized. In

act, at catabolism works better when carbohydrates

are being metabolized. Studies on long-term exercise

and work perormance all indicate the onset o atigue

when glycogen is depleted. Tis again underscores the

importance o adequate carbohydrate intake and glycogen

replenishment. Glycogen depletion is just one actor that

contributes to the onset o atigue. Several other atiguecausing

actors acing athletes include the ollowing:

• ATP and CP depletion

• Lactic acid accumulation

• Calcium ion buildup in muscles

• Oxygen depletion

• Blood pH decrease


Until recently, there were no affordable and easy-to-use

home testing methods that were designed or athletes

to measure key metabolic parameters. Measuring the

state o nitrogen metabolism allows you to determine

whether protein intake is sufficient and also whether

certain supplements are being ingested in amounts that

are sufficient or improving nitrogen balance. Currently

on the horizon is a newly developed testing device that

combines nitrogen balance testing with at metabolism

status. Tese tests measure the output o metabolic waste

products in urine. Tey 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 o

Russian athletes. Tis test provides an economical way to

determine testosterone and cortisol levels in the body by

analysis o saliva. When the body is over trained, cortisol

levels increase. Cortisol is a catabolic hormone that

stimulates the breakdown o muscle tissue. High amounts

in the blood ultimately lead to tissue wasting and negative

nitrogen balance. So, when the testosterone/cortisol

International Sports Sciences Association

26 | Unit 1

ratio is high, anabolism is prevailing. However, when cortisol levels are high and the

ratio is lowered, it is an indication o overtraining. esting testosterone/cortisol ratio

helps you determine whether the body is in a state o overtraining or not. In this way,

you can determine how hard to train, whether to take a ew days off, or i tra ining

intensity should increase.

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.

In addition, in the medical field and in many fitness centers, handheld portable

indirect calorimeters are used that measure oxygen consumption ( • VO 2

) and

determine resting metabolic rate (RMR). As discussed earlier in this unit, the

rate o oxidation or the burning o the calories is different or at, carbohydrate, and

protein. Te ood you eat can either be burned to liberate energy, converted into body

weight, or be excreted. I you light a candle and then place a dome over the candle,

cutting off the fire’s source o oxygen, the fire will go out. In the same way the body’s

ability to undergo oxidation is contingent on oxygen. I the body is getting more

oxygen, it should be burning more calories.

Nutrition monitoring plays a vital role in the care o patients with diabetes, heart

disease, high blood pressure, and obesity, as well as conditions that place patients

at risk or malnutrition, such as cancer, burns, trauma, inection, 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 acilities.


In order to maintain its many chemical and physical activities, the body needs energy.

Earth’s energy originates rom the sun. Plants use solar energy to perorm chemical

reactions to orm carbohydrates, at, and protein. Humans, like other animals,

consume plants and other animals to obtain the energy required to maintain cellular

activities. Tese cellular activities, known as metabolism, are maintained under

homeostatic controls. Te many chemical reactions occurring in the body must be

regulated in order to maintain a balance between the trillions o cells in the body.

Tese cells maintain balance through an intricate organization system. We will now

discuss this intricate organized system known as the body.

Fitness: The Complete Guide

Metabolism | 27

Key Terms

adenosine diphosphate (ADP)

adenosine triphosphate (ATP)

amino acid


anaerobic threshold

ATP/CP pathway

basal metabolic rate (BMR)

beta oxidation

branched-chain amino acids




creatine phosphate (CP)

electron transport chain

fatty acids



glycolytic pathway


ketone bodies

kilocalorie (kcal)

Krebs cycle

lactic acid

maximal oxygen uptake ( VO • 2


metabolic set point



oxidative pathway


respiratory quotient (RQ)

resting metabolic rate (RMR)

thermic effect

training effect

type I muscle fibers

(slow twitch)

type II muscle fibers

(fast twitch)

International Sports Sciences Association

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