Energy - Exercise Sciences!

Transcription

3
Energy
The Ability to Do Work
11/2001
d:\Faculty\Allsen\PE 468\Winning Edge\PE46801EnergyUnit1
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I.
Factors Affecting Performance
A. Strength
1. The ability to exert force
a. Force = mass x acceleration
B. Endurance
1. The ability to exert a force for a given unit of time
a. Speed—explosive endurance
b. Anaerobic endurance (without O2)
c. Aerobic endurance (with O2)
C. Flexibility and Relaxation
1. The ability to take a joint-lever system through a range of motion
2. The time it takes to go through a range of motion
D. Skill
1. The coordination of the nervous and muscular systems
2. The proper sequential firing of motor units
E. Nutrition
1. The utilization of nutrients to provide the various biological systems with usable substances
F. Motivation
1. The ability to endure boredom
2. The ability to endure pain
II.
Systems—developed to control outcomes
A. Homeostasis—The sum total of regulatory functions that maintain a constant environment for
the cells of the body.
1. Body protects itself. A conditioning program must fight through this protection.
III.
Principles of Training
A. Overload principle—subjecting the selected systems of the body to loads greater than those to
which they are accustomed. This overload upsets homeostasis.
1. Duration—length of workload
2. Intensity—difficulty of workload. This variable is important in determining how fast the
training effects are gained. If not controlled properly, it could contribute to overtraining
(athletic staleness).
% Improvement in VO2max
35
RELATIONSHIP BETWEEN TRAINING INTENSITY
& PERCENT IMPROVEMENT IN VO2 max
30
25
20
15
10
20
40
60
80
100
Training Intensity
(%VO2max)
120
140
5
3.
Frequency—number of training sessions per week
a. Recovery—must have adequate time to restore the body systems and allow for
accommodations of the various systems to take place. Things that contribute to this
are: proper nutrition, adequate hydration, proper sleep habits, use of restoration
techniques such as massage therapy, and relaxation/stress management program, and
honest communication between subject being trained and the personal trainer/coach.
4. Mode—type of activity utilized to provide the overload
B. Specificity—specific systems respond to specific training stimuli. In addition to conditioning
specific energy systems, specificity demands that the motor units required to execute a specific
activity be employed and trained during the exercise sessions.
Examples of Changes Due to Training
Both the biochemical and morphological changes taking place in muscle due to training
depend on the functional type of the muscle and the degree of use of the particular muscle in
the training regimen. For example, changes are not identical in muscles containing different
amounts of fast or slow twitch fibers.
ATP content in muscle is not greatly affected by any type of training.
1.
2.
3.
Training with Prolonged Exercise at Moderate Intensities (Aerobic Endurance)
a. Increase in mitochondrial counts
b. Increase in mitochondrial area
c. Increase in phospholipid content of muscle mitochondria
d. Increase in ability to utilize FFA as a substrate during submaximal exercise
e. Increase of glycogen content of muscle
f. Increased activity of Krebs cycle—ETS enzymes that catalyze aerobic oxidation
g. Increase in myoglobin
h. Decrease in adipose tissue
i. Increase in maximum oxygen uptake due to increased cardiac output and increased
ability of cell to utilize oxygen
j. Increase in hemoglobin content
k. Increase in muscle capillaries
Training at High-speed, Intensive Loads (Anaerobic Endurance)
a. Changes in the nervous apparatus of muscle, sarcoplasmic reticulum and the myoglobin
and creatine phosphate contents
b. Increase in the glycolytic enzyme activities
c. Increase in glycogen content
Training at Maximal Power Loads (Strength and Speed Endurance)
a. Increase in cross-sectional area of muscle fiber
b. Increase in number of muscle nuclei
c. Increase in myosin and actin and myostromine content. Myostromine refers to the
protein complex of the muscle stroma remaining after extraction of both water soluble
proteins and myosin.
d. Elevated ATPase potential
e. Increase in amount of connective tissue. Thought to be due to an increase in
collagenous fibrils, which add to the tensile strength of ligaments and tendons.
6
It’s Never Too Late to Reap the Benefits
middle-aged men are any indication, the tides of time need not rob any of us of our youthful edge. In a
recent study published in the journal Circulation, the effects of a 30-year layoff were reversed with six
months of exercise training. The study began with five healthy 20-year-old men in 1966 in research
designed to examine the effects of three weeks of bed rest on aerobic capacity. After a six-month program of aerobic
exercise that gradually increased to one hour, four or five times a week, they regained the fitness lost during the
previous 30 years.
These findings were surprising in two ways. First, time had taken its toll on these men. Their weight had
increased by 25%, body fat had doubled, and aerobic capacity had decreased by 11% during the 30-year period.
Despite that, they were able to achieve the same degree of cardiovascular fitness they had as 20-year-olds with a
regular, moderate exercise program.
This is encouraging to anyone whose fitness routines are interrupted—it’s never to late to get it back. A
second and even more surprising finding was uncovered in this study; three weeks of bed rest at 20 years of age was
worse for physical capacity than three decades of aging. Despite the implications for potential layoffs, don’t despair:
the loss is always reversible. (Circulation, 2001, Vol. 104, pp. 1350–1357)
IF
7
C.
Reversibility—the gains made through training are lost when the overload of training is removed.
Examples of Reversibility Principle
Detraining occur rapidly when a person stops exercising. After only 1 or 2 weeks of
detraining, significant reductions in both metabolic and working capacity can be measured, and
many of the training improvements are lost within several months.
N
Sex
Duration (Days)
5
M
20 (bedrest)
7
F
17
9
M
M
6
1
M
F
84
70
35
56
D. Cell
Variable
Max VO2 1 @ min-1
Stroke volume, ml @ beat-1
Cardiac output, 1 @ min-1
Max VO2, ml @ kg-1 @ min-1
VE max, 1 @ min-1
O2 pulse, ml @ beat-1
Sum of 3-min recovery heart rate
CP, mmols @ g wet wt-1
ATP, mmols @ g wet wt-1
Glycogen, mmols @ g wet wt-1
Elbow extension strength, ft-lb
Max VO2, 1 @ min-1
Max VO2, ml @ kg @ min-1
HR max, 1 @ min-1
Stroke volume, ml @ beat-1
Cardiac output, 1 @ min-1
Max a-v@ O2 diff, ml @ 100 ml-1
Citrate synthase, mol @ kg protein-1 @ h-1
SDH mol @ kg protein-1 @ h-1
Pre-Detraining
Average
Post-Detraining
Average
3.3
116
20
47.8
77.5
12.7
190
17.9
5.97
113.9
39.0
4.22
62.1
187
148
27.8
15.1
10.0
4.43
2.4
88
14.8
40.4
69.5
10.9
237
13.0
5.08
57.4
25.5
3.67
53.2
199
127
25.2
14.5
6.0
2.73
Percent
Change
-27
-24
-26
-15.5
-10.3
-14.2
-24.7
-27.4
-14.9
-49.6
-34.6
-14
-14
+6
-14
-9
-19
-40.6
-38.4
8
Structure and Function of Cellular Components
COMPONENT
STRUCTURE
FUNCTION
Cell (plasma) membrane
Sarcolemma in muscle
membrane composed of phospholipids and
protein molecules
gives form to cell and controls
passage of materials in and out
Cytoplasm (sarcoplasm)
fluid, jelly-like substance in which organelles
are suspended
serves as matrix substance in which
chemical reactions occur
Endoplasmic reticulum
(Sarcoplasmic reticulum)
system of interconnected membrane forming
canals and tubules
supporting framework within
cytoplasm; transports materials and
provides attachment for ribosomes
Ribosomes
granular particles composed of protein and
RNA
synthesize proteins
Golgi apparatus
cluster of flattened, membranous sacs
synthesizes carbohydrates and
packages molecules for secretion and
secretes lipids and glycoproteins
Mitochondria
membranous sacs with folded inner partitions controls aerobic energy
transformations
Lysosomes
membranous sacs
digest foreign molecules and worn
and damaged cells
Centrosome
nonmembranous mass of two rod-like
centrioles
helps organize spindle fibers and
distribute chromosomes during
mitosis
Vacuoles
membranous sacs
store and excrete various substances
within cytoplasm
Fibrils and microtubules
Myofibril in muscle cell
thin, hollow tubes
protein filaments actin and myosin
support cytoplasm and transport
materials within the cytoplasm
Cilia and Flagella
minute cytoplasmic extensions from cell
move particles along surface of cell or
move cell
Nuclear membrane
membrane composed of protein and lipid
molecules surrounding nucleus
supports nucleus and controls
passage of materials between
nucleus and cytoplasm
Nucleolus
dense, nonmembranous mass composed of
protein and RNA
forms ribosomes
Chromatin
fibrous strands composed of protein and DNA controls cellular activity for carrying
on life’s processes
9
Types of Movement Through Cell Membranes
PROCESSES
CHARACTERISTICS
ENERGY SOURCE
EXAMPLE
Diffusion
passive movement of molecules to regions
of lower concentration from regions of
higher concentration
molecular motion
exchange of respiratory
gasses in the lungs
Facilitated diffusion
carrier substances are used to speed
process
carrier energy and
molecular motion
glucose entering cell
Osmosis
passive movement of solvent molecules
through semipermeable membrane due to
a concentration difference of water
molecular motion
water movement through cell
wall to maintain constant
turgidity of cell
Filtration
molecules are forced by hydrostatic
pressure from regions of higher pressure
to regions of lower pressure
blood pressure
removal of waste within
kidneys
Active transport
molecules or ions are transported through
cell membrane by other molecules
cellular energy (ATP)
movement of glucose and
amino acids through
membranes
Pinocytosis
membrane engulfs minute droplets of fluid
from surroundings
cellular energy
membrane froms vacuoles
containing solute and solvent
Phagocytosis
membrane engulfs solid particles from
surroundings
cellular energy
white blood cell membrane
engulfs bacterial cell
Muscle Cell
Mucsle Cell Contents
75%
5%
20%
H2O
inorganic salts, pigments, and substrates
a mixture of proteins
1. 12% myofibrillar proteins
2. 8%
enzymes, membrane proteins, transport
channels, and other proteins
10
1.
2.
Semi-permeable Membrane
a.
Composed of protein-fat-protein
b.
Filled with holes
c.
Has an electrical charge, positive on the outside and negative on the inside
Ion (Electrolyte)—A charged particle
IONIZATION
NaCl !!H
!!!!O!6 Na+ + Cl2
3.
4.
Hydrolysis—the breaking of a chemical bond with water
Mitochondria—Aerobic powerhouses of the cell that control aerobic energy transformations.
IV.
Energy—the ability of the body to do work. Energy is the purchasing power used to do work. Work is measured by the ability
to utilize energy.
V.
Fatigue—inability to produce or expend energy at a given intensity and duration.
VI.
Forms of Energy
A. Potential energy—affected by position or condition
Position
Condition
energy released
energy
e
e
transfer
H+
H
Electron Transfer System
Joint Lever System in the
Human Body
• Mechanical advantage—ratio
of force arm to resistance arm.
1.
C6H12O6
C51H98O6
Training programs change the condition of chemical systems in the body
CONDITION
SYSTEMS
Example:
9
9
8potential energy
control outcomes
9
9
8the amount of energy to do work
8performance
11
B. Kinetic energy—energy due to motion. Affected by mass and speed.
1. Weight—force with which a body is attracted to the earth. Due to the law of gravity.
2. Mass—the quantity of matter in a body.
ENERGY
(Ability To Do Work)
Genetics
Proper
Conditioning
Program
C. Body composition
1. Fat mass
a. Essential fat—fat incorporated into organs and tissues such as nerves, brain, heart,
muscle, bone marrow, lungs, liver, and mammary glands
(1) Males = about 3%
(2) Females = about 12%—includes sex-specific fat in breasts and reproductive
organs
b. Storage fat—stored in fat cells (adipose tissue)
2. Fat free mass
a. The part of the body made up of protein, water, minerals, and carbohydrate. Found in
muscle tissue, connective tissue, skeletal tissue, nervous tissue, organs, blood, and
teeth.
3. Lean body mass—includes fat free mass plus essential fat
D. Types of energy
1. Chemical
2. Electrical
3. Mechanical (kinetic)
4. Thermal (heat)
5. Radiant (light)
6. Nuclear
VII. Thermodynamics
A. First law—energy cannot be created or destroyed, but it can be converted from one form to
another
B. Second law—energy tends to become disorganized (entropy) and seeks heat as its final form
1. Efficiency rating—the ratio of energy released to the amount used to do work and the
amount released as heat.
Example:
a. Amount released = 100 units
b. Amount used to do work = 44 units
c. Amount released as heat = 56 units
d. Efficiency rating = 44%
Between 75 and 80 percent of the energy produced from cellular metabolism is released in
the form of heat.
12
VIII. Enzyme System = substrate + enzyme 6 product
A. Enzymes—organic catalysts. Their presence lowers the amount of activation energy (energy needed to
start a reaction), and in the body they increase the rate of reaction. They are not changed by the reaction.
Co-factors
Apo-enzyme + (minerals) !6 Holo-enzyme
(protein)
Co-enzymes
(vitamins)
1.
2.
3.
Example: in a typical mitochondrion, there may be as many as 10 billion enzyme molecules, each
carrying out millions of operations within a short time. The specific reaction can be 106 to 1012 times
faster than one not controlled by enzymes.
Enzymes are specific, they will only react with specific substrates.
Rate limiting enzyme—in a metabolic pathway you only need to affect a specific enzyme, known as
a rate limiting enzyme, to control the rate of reaction.
Inhibition
Rate-Limiting
Enzyme
A
Substance
1
Enzyme
B
Substance
2
Enzyme
C
Substance
3
Enzyme
D
Substance
4
Product
An example of a “rate-limiting” enzyme in a simple metabolic pathway. Here, a buildup of the
product serves to inhibit the rate-limiting enzyme, which in turn slows down the reactions involved
in the pathway.
13
B. Substrate—that substance that is acted upon by the enzyme. The product of one enzyme can
become the substrate for another enzyme.
Example:
A metabolic pathway, where the product of one enzyme becomes the substrate of
the next in a multienzyme system.
Enz 1
Enz 2
Enz 3
Enz 4
A&&&&&6B&&&&&6C&&&&&6D&&&&&6Final Product
C. Questions to be asked concerning training programs
1. What systems are used in the activity?
2. What are the stimuli (overloads) necessary to change the condition of the systems?
D. Metabolism—The sum total of the chemical changes or reactions occurring in the body.
1. Catabolism (Depolymerization)—The breaking down of complex chemical substances into
simpler units
2. Anabolism (Polymerization)—The building of complex chemical substances from simpler
chemical units
Large Molecules
Large Molecules
ATP
CATABOLISM
Energy
ANABOLISM
Heat
Energy
ADP
Small Molecules
Small Molecules
Catabolic reactions = exergonic: energy-releasing reactions
Anabolic reactions = endergonic: energy-consuming reactions
Factors affecting the rate of activity of enzyme systems.
1. Concentration of enzyme
2. Concentration of substrate
3. Temperature—determines the direction of a chemical reaction and whether we have control
of the reaction.
a. Q10 effect—each 10ºC increase in temperature doubles the rate of an enzymatic
reaction.
15
Rate of Reaction (arbitrary units)
E.
Range of Muscle
Temperature
Q10 EFFECT
10
Illustration of a Q10 effect,
where each 10ºC increase in
temperature doubles the rate of
reaction. In the physiological
range (shaded area) the curve
is very steep
5
0
10
20
30
40
Temperature (ºC)
50
14
b.
During strenuous exercise heat production can increase as much as 100 times that of a muscle
at rest. If this heat is not removed from the body, the internal temperature can rise 1ºC every
5–8 minutes and thus the risk of heat illness (hyperthermia) can occur. In order to maintain the
temperature in a range where control of chemical reactions can take place, most of the heat is
released through the evaporation of sweat. It is the evaporation that is critical as for every gram
of sweat evaporated, approximately .58 kcal of heat is removed.
Methods of Heat Loss
•
Conduction
•
Convection (wind chill factor)
•
Radiation
•
Evaporation
One of the problems with sweating and evaporation is the removal of fluid from the body. If
this fluid is not replaced, the blood volume can decrease and there are serious consequences due
to the effects of dehydration. Thirst is not an adequate guide to the amount of water required,
and a method to monitor fluid loss is needed. Following is a procedure that works quite well.
•
Before Activity
1. Check color of urine – clear like lemonade = hydrated; –dark brown =
dehydrated
2. Weight subject after becoming hydrated
•
During activity
2. Replace Fluids
•
After Activity
1. Weigh Subject
2. For every pound of weight lost, replace with 1.5 pints of fluid (1 pint = 1
pound). The extra .5 pint of fluid per pound of weight lost will insure that the
fluid lost as urine is being replaced.
4.
pH—determines the direction of a chemical reaction and whether we have control of the reaction.
a. pH = relative number of H+ in a solution
b. Acid—a substance that gives up H+ in a solution
(1) Strong acid—gives up H+ rapidly, i.e., lactic acid
(2) Weak acid—gives up H+ slowly, i.e., carbonic acid
c. pH—Increasing pH by one pH unit changes the concentration of H+ by the factor of 10. There
is 10 times less H+ in a pH 8.0 solution than in a pH 7.0 solution.
Accumulation
of acids
Loss of
bases
Increase concentration
of H+
Acidosis
pH scale
pH drops
7.4
pH rises
Akalosis
Decrease concentration
of H+
Loss
of acids
(1) Normal pH of muscle cell = 7.0
(2) Normal pH of oxygenated blood = 7.4
Accumulation
of bases
15
d.
5.
Problems with increased hydrogen ions
(1) Stimulate pain nerve endings
(2) Cause fatigue by reduced ATP production due to enzyme changes, changes in
membrane transport mechanisms, and changes in substrate availability
(a) Enzymes—inactivate rate limiting enzymes
(b) Membranes—affect carriers in membrane or permeability of the membrane
(c) Substrate—glycogen breakdown to glucose is slowed and fatty acid utilization
is decreased. Use of phosphocreatine is accelerated and soon becomes
depleted
(3) Reduced force and velocity of muscle contraction
(a) Inhibition of actomyosin ATPase
(b) Interference of H+ with action and uptake of Ca++.
Example:
Lactic Acid
lactic acid
anaerobic
C6H12O6 ————————————÷ 2C3H6O3
glycolysis
glucose
C3H6O3 (lactic acid) ——÷ H+ (hydrogen ion) + C3H5O3- (lactate)
Presence of modulators—turn the enzyme system on or off. The end products of one system
can become the modulators for another system.
System
Rate-Limiting Enzyme
Activators
Inactivators
ATP-PC system
Creatine kinase
ADP
ATP, CP, citrate,
FFA, pH
Glycolysis
Phosphofructokinase
ADP, Pi, pH
ATP
Glycolysis
Phosphorylase
Ca++, cyclic AMP
ATP
Krebs cycle
Isocitrate dehydrogenase
ADP, Pi
ATP
Electron transport chain
Cytochrome oxidase
ADP, Pi
ATP
a.
b.
Hormones—important modulators. Catalytic type substances which affect chemical
reactions, but are changed by the reaction when it takes place
Nature of hormones
(1) Hormones can be classified as either steroid or nonsteroid. Steroid hormones are
lipid soluble and most are formed from cholesterol. Nonsteroid hormones are
proteins, peptides, or amino acids
16
(2) Hormones are generally secreted into the blood and then circulate through the
body to exert an effect on their target cells. They act by binding in a lock and key
manner with specific receptors found only in the target tissues
(3) Steroid hormones pass through cell membranes and bind to receptors inside the
cell. They use a mechanism called direct gene activation to cause protein
synthesis.
(4) Nonsteroid hormones cannot enter the cell easily, so they bind to receptors on the
cell membrane. This activates a second messenger within the cell which in turn
can trigger numerous cellular processes.
(5) Secretion of most hormones is regulated by a negative feedback system. Negative
feedback describes the response from a control system that reduces the size of the
stimulus. For example, an elevated blood glucose concentration causes the
secretion of the hormone insulin which, in turn, lowers the blood glucose
concentration.
(6) The number of receptors for a specific hormone can be altered to meet the body’s
demands. Up-regulation refers to an increase in receptors, and down-regulation is
a reduction. These two processes change cell sensitivity to hormones.
17
PRINCIPAL ACTIONS OF HORMONES AND SOME
IMPORTANT OUTCOMES OF THOSE ACTIONS
EXPECTED RESULTS OF
HORMONE
GENERAL ACTIONS OF HORMONES
HORMONE ACTIONS
Insulin
8Uptake of Glucose from Blood
8Glycogen Synthesis
8Uptake of Amino Acids from Blood
8Protein Synthesis
9Fat Breakdown
8Fat Synthesis
9Blood Glucose
8Glycogen in Muscle & Liver
9Blood Amino Acids
8Protein in Tissues
9Fatty Acids in Blood
8Fat Stores in Tissues
Glucagon
8Breakdown of Glycogen in Liver
8Production of Glycogen in Liver
from Amino Acids and Lactic Acid
8Fat Breakdown
8Blood Glucose
8Blood Glucose
Epinephrine (EPI)
Norepinephrine (NOREPI)
Cortisol
Growth Hormone (GH)
Testosterone
8Breakdown of Glycogen in Liver
9Glycogen in Liver; 8Blood Glucose
8Breakdown of Glycogen in Muscles 9Glycogen in Muscle
8Fat Breakdown
8Production of Glycogen in Liver
from Amino Acids and Lactic Acid
8Fat Breakdown
8Protein Breakdown
8Blood Glucose
9Amino Acids Incorporation into
Proteins
8Amino Acids in Blood
9Uptake of Glucose from Blood
8Uptake of Amino Acids from Blood
8Protein Synthesis
8Fat Breakdown
8Blood Glucose
9Blood Amino Acids
8Protein in Tissues
Stimulates Growth
8in Protein Anabolism,
Development, and Maintenance of
Male Sex Characteristics
8Striated Muscle Size
9Body Fat
Insulin‐like Growth Factors (IGF) 8Protein Synthesis in Cell
Erythropoietin (EPO)
Stimulates Red Bone Marrow to
Produce Red Blood Cells
8Striated Muscle Size
8O2 Transport
8O2 Utilization
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11/2001
d:\Faculty\Allsen\PE 468\Winning Edge\PE46801EnergyUnit2
ATP—ADENOSINE TRIPHOSPHATE
I.
ATP—stored chemical energy that links the energy-yielding and energy-requiring functions within
all cells.
Uses of ATP
Muscle Contraction
8
a
b
Digestion
Secretion by Glands
_
`
ATP
9
Nerve Transmission
Circulation
Building New Tissue
A.
Simplified structure of ATP, showing high energy phosphate bonds
High-Energy
Phosphate Bond
Adenosine
A
B.
P
P
Energy
P
Adenosine
P
P
Pi
B
Breakdown of ATP to ADP and inorganic phosphate (Pi), with the release of useful energy.
The breakdown of 1 mole of ATP yields between 7 and 12 kilocalories (kcal) of energy.
1.
Calorie—measurement of energy
a.
Small calorie—amount of energy necessary to raise 1 gram of water 1ºC
b.
Large calorie (kilocalorie-kcal) (Calorie)—amount of energy to raise 1
kilogram (l liter) of water 1ºC
2.
Gram molecular weight (mole/mol)—the molecular weight of a substance expressed
in grams. The weight of the molecule is attained by totaling the atomic weight of its
constituent atoms
ATP
= 5N
(14)
70
10 C (12)
120
13 O (16)
208
15 H (1)
15
3P
(31)
93
506 grams
a.
One mole of any substance contains 6.023 x 1023 molecules
19
C.
D.
Storage of ATP in the body
1.
The body does not store a great amount of ATP
a.
One gram mole = 506 grams 6 12 kcals
b.
Stored ATP in body = 85 grams 6 2.04 kcals. The cost of going 1 mile =
100–150 kcals
c.
By keeping the normal level of ATP low, any small utilization immediately
changes the level markedly and stimulates the enzyme systems that generate
ATP. ATP is an important modulator for these enzyme systems
d.
Body produces about 120 pounds of ATP per day to maintain the resting
metabolic rate (RMR) and the cost of 120 pounds of artificial ATP is about
$750,000
Coupled reactions—the functional coupling of energy from one series of reactions to run
another reaction
1.
Phosphocreatine (PCr/CrP)—an energy-rich compound that plays a critical role in
releasing energy to produce ATP
PCr——————6 Pi + Cr
energy
coupled reaction
ú
2.
ADP + Pi ———————6 ATP
Energy releasing foods
a.
One gram of CHO 6 4 kcals
b.
One gram of fat 6 9 kcals
Food——————6 end-products
energy
ú
coupled reaction
ADP + Pi ———————6 ATP
I.
II.
CARBOHYDRATE (CHO)
Simple Carbohydrates
A.
Monosaccharides
1.
Glucose (C6H12O6)
2.
Fructose
3.
Galactose
B.
Disaccharides
1.
Sucrose
=
glucose + fructose (table sugar)
2.
Lactose
=
glucose + galactose
3.
Maltose
=
glucose + glucose
Complex Carbohydrates (starches)
A.
Polysaccharide—combination of 3 or more glucose molecules
B.
Glucose polymer—combination of 10 or more glucose molecules
1.
Maltodextrin and polycose are common forms of glucose polymers used in sport
drinks.
2.
Glucose polymers are prepared commercially by controlled hydrolysis of starch, such
as cornstarch
3.
Muscle and liver glycogen are glucose polymers and are important in producing
energy in the body to do work.
20
C.
Source of dietary fiber
1.
Water soluble fiber—gums and pectins
2.
Water insoluble fiber—cellulose, hemicellulose, lignin
III.
Water and Glycogen Metabolism—approximately 2.7 grams of water are stored with each gram of
glycogen
IV.
Storage of Carbohydrate in the Body
SOURCE
AMOUNT
KCALS
Blood glucose
5 grams
20
Liver glycogen
75–100 grams
300–400
Muscle glycogen
12 g per kg muscle (about 300 grams)
60/kg muscle 1440
Note: Muscle glycogen is muscle cell specific and certain tissues such as nervous tissue, retina, and
red blood cells, depend on blood glucose as the only source of energy.
V.
Fatigue and Carbohydrate
A.
Fatigue may be attributed to:
1.
Decreased blood glucose = 3.3 mmol or less
2.
Decreased muscle glycogen = 50 mmol per kg of wet muscle or less
VI.
Carbohydrate Intake of Athletes
A.
Current diet: 49% CHO, 36% Fat, 15% Protein
B.
Recommended CHO intake for athletes = 60% or greater or about 4 grams of CHO per
pound of body weight.
VII
Effects of Various Carbohydrates
A.
Rate of fluid absorption
1.
Glucose, maltodextrins, and sucrose are similar
2.
Fructose absorbed much slower and does not stimulate as much fluid absorption
B.
Effect on performance
1.
Glucose, maltodextrins, and sucrose have similar effects on performance
2.
Fructose is not associated with an increase in performance. This may be due to
inability of the liver to metabolize and release the glucose formed from fructose
rapidly enough to be useful at the cellular level.
ENERGY RELEASING SYSTEMS
Read article in appendix at end of this unit
A.
Sports Nutrition, p. 52
I.
Anaerobic Systems
A.
ATP-PC system
B.
Anaerobic glycolysis
II.
Aerobic Systems
A.
Aerobic glycolysis
B.
Krebs cycle
C.
Electron transfer system—ETS (uses O2)
21
III.
Rate—time it takes to do something
IV.
Capacity—total amount that can be accomplished
V.
Maximal Rates of ATP Formation
A.
ATP-PCr system—11 mmol ATP per second
B.
Anaerobic glycolysis—5 mmol ATP per second
C.
Aerobic systems (CHO)—2 mmol ATP per second
D.
Aerobic systems (Fat)—1 mmol ATP per second
VI.
Time to Reach Maximum Output
A.
Glycolysis—at least one minute
B.
Oxidative—two to three minutes
VII.
Rate and Capacity for Energy Production
Rate of ATP Production
Capacity of ATP Production
ATP-PC
1
4
2
3
Aerobic glycolysis
3
2
Krebs Cycle-ETS
4
1
1 = Highest
2
3
4 = Lowest
ATP-PC System
1.
ATPase
Stored ATP —————6 ADP + Pi + energy for work + heat
H2O
2.
CPK
Stored PCr——————6 Pi + Cr + heat
energy
ú
coupled reaction
ADP + Pi ———————6 ATP
ATP and PCr are stored within the muscle in very small quantities. This system can deliver energy
very quickly, but cannot support work for long periods.
Half Life—the amount of time needed to recover 50% of a system or a substance
A.
ATP-PC system = 20 to 30 seconds
B.
Lactic acid = 15 to 25 minutes
22
Replenishment of Phosphagen Stores
Half-life = 20–30 Seconds
ATP-PC System
Recovery Time = Seconds
Recovery Time
0
20
40
60
80
100
120
140
160
180
200
Percentage Replenished
0.00
50.00
75.00
87.50
93.75
96.88
98.44
99.22
99.61
99.80
99.90
Recovery Time
0
30
60
90
120
150
180
210
240
270
300
Removal of Lactic Acid
Half-life = 15–25 Minutes
Anaerobic Glycolysis
Recovery Time = Minutes
Recovery Time
0
15
30
45
60
75
90
105
120
135
150
Percentage Removed
0.00
50.00
75.00
87.50
93.75
96.88
98.44
99.22
99.61
99.80
99.90
Recovery Time
0
25
50
75
100
125
150
175
200
225
250
Inside mitochondria
Inside mitochondria
ETS ← H ← beta oxidation
FFA
2 Pyruvic acid
4H → ETS
Hydrogen
Acetyl CoA
YES
YES
12H2O
30– –cardiac muscle
28– –skeletal muscle
2
2
YES
↑
16H, 4CO2
2
3
1 ATP per 1 PCr
NO
NO
NO
NET ATP PRODUCED
O2
NEEDED
34%
2%
3%
100%
Aerobic
Anaerobic
Speed
(explosive)
Lactic acid
Oxidative
Aerobic glycolysis
Krebs cycle
Electron Transfer System
A
Phosphagen
ATP-PCr
Aerobic
Anaerobic
Anaerobic
ENERGY SYSTEMS
Aerobic endurance
Anaerobic endurance
Speed (explosive) endurance
Jogging
440-yard
run
50-yard
dash
shot-put
TYPE OF
ENDURANCE EXAMPLE
*The formation of lactic acid or pyruvic acid depends on mitochondrial activity, not on the presence of O2.
†Glucose is the primary substrate for aerobic (slow) glycolysis and muscle glycogen is the primary substrate for anaerobic (fast) glycolysis.
Electron
Transfer
System
Krebs
Cycle
Glucose
Aerobic*
glycolysis
(slow)
2HL
2HL
ADP + Pi
Pi + Cr
END PRODUCT
pyruvic acid—6 4H, 2CO2
↓
ETS
Glucose†
Glycogen
Anaerobic* Outside mitochondria
glycolysis
(fast)
Outside mitochondria
ATP PCr
Outside mitochondria
ATP-PCr
SUBSTRATE
LOCATED
SYSTEM
%
IMMEDIATE
ENERGY
OBTAINED
ENZYME SYSTEMS TO RELEASE ENERGY TO PRODUCE ATP
23
24
Energy Releasing Systems Using Carbohydrate
Stage I: Glycolysis
Summary of Glycolysis
A. Anaerobic
B. Occurs in cytoplasm
C. ATP production GLU
+ 4 ATP (steps 7 and 10)
- 2 ATP (steps 1 and 3)
2 ATP (net)
D. ATP Production GLY
+ 4 ATP (steps 7 and 10)
- 1 ATP (step 3)
3 ATP (net)
E. 2 NADH + H+
F. 2 Pyruvate
PERCENT OF IMMEDIATE ENERGY OBTAINED (ATP)
Aerobic Glycolysis—Krebs Cycle—Electron Transfer System
32 moles ATP/mole x 7.3 kcal/mole ATP
—————————————————— = 34%
686 kcal/mole glucose
3 moles ATP/mole x 7.3 kcal/mole ATP
—————————————————— = 3%
2 moles ATP/mole x 7.3 kacal/mole ATP
—————————————————— = 2%
25
Glycolysis
NADH + H+
Sarcoplasm
Lactic acid
LDH
Pyruvic acid
Mitochondrial membrane
“Hydrogen shuttle”
Mitochondrion
H+
Failure of the mitochondrial “hydrogen shuttle” system to keep
pace with the rate of glycolytic production of NADH + H+
results in the conversion of pyruvic acid to lactic acid.
Mitochondrial Membrane Shuttles
•
Striated muscle = glycerol phosphate shuttle
•
Cardiac muscle = malate-aspartate shuttle
Stage II: The Formation of Acetyl Coenzyme A
26
Stage III: The Krebs Cycle
Summary of Krebs Cycle
A. Does not directly utilize O2
B. Occurs in mitochondrial matrix
C. 1 ATP (step 8)
D. 3 NADH + H+ (steps 5, 7, and 11)
E. 1 FADH2 (step 9)
F. 2CO2
Release of Hydrogen
System
Hydrogen
Aerobic glycolysis
4
Pyruvic acid to acetyl CoA
4
Krebs Cycle
16
Total
24
Biological oxidation in energy releasing systems
A.
Removal of hydrogen
B.
Transfer of electrons
Oxidation-Reduction Reactions
Reducing agent—the molecule that gives up electrons
Oxidizing agent—the molecule that accepts electrons
Oxidation does not mean oxygen is always involved in the process. The term oxidation is derived
from the fact that oxygen has the tendency to accept electrons. Cells make use of this fact by using
oxygen as the final electron acceptor in the electron transfer system.
27
Stage IV: Electron Transport and Oxidative Phosphorylation
Historically, it was estimated that the aerobic metabolism of one molecule of glucose produced 38 molecules of ATP.
Research reveals that only 32 ATP actually enter the cytoplasm to do work. This conclusion is due to the fact that the
energy provided by NADH and FADH is required not only for ATP production, but also to transport ATP across the
mitochondrial membrane. This added energy cost of ATP metabolism reduces the estimates of the net ATP yield
from glucose.
ENERGY RELEASING SYSTEMS USING FAT
I.
Energy pathways for fatty acids. Triglycerides in the
adipose tissue may be catabolized by hormone-sensitive
lipase, with the fatty acids being released to the plasma and
binding with albumin; the glycerol component is transported
to the liver for metabolism. A receptor at the muscle cell
transports the fatty acid into the muscle cell where it is
converted into fatty acyl CoA by an enzyme (fatty acyl CoA
synthetase). The fatty acyl CoA is then transported into the
mitochondria with carnitine (in an enzyme complex) as a
carrier. The fatty acyl CoA, which is a combination of
acetyl CoA units, then undergoes beta-oxidation, a process
that splits off the acetyl CoA units for entrance into the
Krebs cycle.
28
Beta Oxidation
Possible mechanisms associated with the increased
use of fat as an energy source during aerobic
endurance exercise following exercise training.
Fat energy sources during exercise
Plasma
Not a major source
chylomicrons
Plasma VLDL Not a major source
Plasma FFA
Major source: Replenished by adipose
cell release of FFA; Used in exercise at
low to moderate intensity, i.e., 25–65
percent VO2 max; Use decreases as
exercise intensity increases toward 65
percent VO2 max
Muscle FFA
Major source; Released from
intramuscular triglycerides; Low use
during mild exercise; Used
increasingly as exercise intensity
increases toward 65 percent VO2 max
Note: With high-intensity exercise, 65 percent VO2 max or higher,
total fat oxidation falls.
% Fat/CHO in Exercise Metabolism
• Increased blood flow and capillarization to the muscle,
delivering more plasma FFA.
• Increased muscle triglyceride content, possibly
associated with increased insulin sensitivity. Insulin
regulates movement of FFA into muscle cells. Exercise
training may also increase the activity of lipoprotein
lipase or fatty acid transporters at the muscle cell
membrane.
• Increased sensitivity of both adipose and muscle cells to
epinephrine, resulting in increased FFA release to the
plasma and within the muscle from triglycerides.
• Increased number of fatty acid transporters in the
muscle cell membrane to move fatty acids from the
plasma into the muscle cell.
• Improved ability to use ketones as an energy source.
• Increased number and size of mitochondria, and
associated oxidative enzymes for processing of
activated FFA.
• Increased activation of FFA and transport across the
mitochondrial membrane.
• Increased activity of oxidative enzymes.
100
Shift From CHO Metabolism Toward Fat Metabolism
During Prolonged Exercise
% Fat
80
60
40
% CHO
20
0
10
30
50
Exercise Time (min)
70
90
29
III.
Fat Storage
A.
It cost CHO and protein approximately 25% of their total calories to convert them to storage
fat
B.
It costs dietary fat approximately 3% of the total calories to convert to storage fat
C.
Dietary fat doesn’t require extensive chemical changes to be stored as body fat
D.
Calories Do Count: 1 gram of fat 6 9 kcals • 1 gram of protein 6 4 kcals • 1 gram of CHO 6 4
kcals
Dietary Intake
Weight
Fat = 100 grams
CHO = 100 grams
IV.
kcals
900
400
Energy Used to
Convert to Storage Fat
27 kcals
100 kcals
Kcals as Storage Fat
873
300
Need for Carbohydrate in Order to Metabolize Fat
The breakdown of fatty acids depends on a continual background level of carbohydrate breakdown.
Acetyl Co-A enters the Krebs Cycle by combining with oxaloacetic acid (which is primarily
produced by carbohydrate metabolism) to form citric acid. This degradation of fatty acids by the
Krebs Cycle continues only if sufficient oxaloacetic acid is available to combine with acetyl Co-A
formed during beta oxidation. The pyruvic acid formed during glucose breakdown may play an
important role in furnishing this oxaloacetic intermediate. When carbohydrate levels fall,
oxaloacetic acid levels may become inadequate to sustain a high level of fat breakdown. In this
sense, “fats” burn in a carbohydrate flame.
It is also likely that there may be a rate limit to fatty acid utilization by the exercising muscle.
Although this limit can be greatly enhanced by aerobic type exercise training, the aerobic muscle
power generated only by fat breakdown never appears to equal that generated by combined fat and
carbohydrate metabolism. Thus, the maximum power output of muscle declines when muscle
glycogen becomes depleted.
An appreciable reduction in carbohydrate availability, which could occur in prolonged exercise such
as marathon running, consecutive days of heavy training, inadequate caloric intake, dietary
elimination of carbohydrates (as advocated with high-fat, low-carbohydrate “ketogenic diets”) or
diabetes seriously limits the capacity for energy transfer. This occurs although large amounts of
fatty acid and substrate are available in the circulation. In instances of extreme carbohydrate
restriction or depletion, the excess acetyl Co-A produced in beta oxidation is taken to the liver and
metabolized to ketones or ketone bodies. If the ketones are not used but, instead, accumulate, a
condition called ketosis or acidosis occurs. The high acidity of ketosis can disrupt normal
physiological functioning, especially the acid-base balance. During exercise aerobically trained
individuals can utilize ketones more effectively than untrained individuals.
30
V.
Metabolic Mill—explains the important conversions between carbohydrates, lipids (fats), and
protein metabolism.
VI.
Substrate Availability and Utilization
Estimated Maximal Power and Capacity for Untrained (UT) and Trained (TR) Males
Power
kcal @ min-1
Capacity
kj @ min-1
kcal @ min-1
kj @ min-1
System
UT
TR
UT
TR
UT
TR
UT
TR
Phosphagens (ATP-PC)
72
96
300
400
11
13
45
55
Anaerobic glycolysis (LA)
36
60
150
250
48
72
200
300
Aerobic glycolysis plus
Krebs cycle plus ETS/OP
(O2)
7–19
32–37
30–80
135–155
360–
1270
10,770–
19,140
1500–
5300
45,000–
80,000
Source: Modified from Bouchard, Taylor, & Dulac;13 Bouchard et al.14
31
Relative Degree of Fuel Utilization in Muscle for Various Types of Exercise
Exercise Condition
Fuel
Very High
Intensity,
Very Short
Duration
(<3 min),
and Static
Contractions
Negligible
High-Intensity
(80–85% max),
Short- Duration
(<40 min)
High-Intensity
(70–80% max),
ModerateDuration
(40–150 min)
ModerateIntensity
(60–70% max),
Long-Duration
(>150 min)
LowIntensity
(<50% max),
LongDuration
(>150 min)
High
High
High
Moderate
Low
Moderate
Negligible
High
High
Moderate
Moderate
Moderate
Negligible
Low
Moderate
High
High
Low
Negligible
Negligible
Low
Low
Low
Rest
Muscle
glycogen
Liver
glycogen and
bloodborne
glucose
Free fatty acid
(FFA)
Amino acid
Sources: Based on Felig & Wahren,14 Pernow & Saltin,14 Saltin.16
PRACTICAL APPLICATION OF ENERGY RELEASING SYSTEMS
I.
II.
Bioenergetics and Maximal Effort Duration
Primary system
Duration of event
ATP-PC
ATP-PC + anaerobic glycolysis
Anaerobic glycolysis + aerobic systems
Aerobic systems
< 10 sec
10–30 sec
30 sec–2 min
2 min–3 min
>3 min and rest
Duration of Maximal Exercise
Seconds
Percent aerobic
Percent anaerobic
10
10
90
30
20
80
Minutes
60
30
70
2
40
60
4
65
35
10
85
15
30
95
5
60
98
2
120
99
1
32
III.
Primary Energy Sources
PRIMARY ENERGY SOURCES

ATP-PC, Lactic
Acid, and Oxygen
Systems
ATP-PC and Lactic Acid Systems
% Aerobic
% Anaerobic
Event (meters)


Oxygen System
0
10
20
30
40
50
60
70
80
90
100
100
90
80
70
60
50
40
30
20
10
0






100
200
400
5000
10,000


800

1500 3200
(2 miles)
Time (min:sec)
IV.
0:10
0:20
1:45
3:45 9:00
14:00
29:00
135:00
Major Characteristics of the Human Energy Systems
Keep in mind that during most exercises all three energy systems will be operating to one degree or
another. However, one system may predominate, depending primarily on the intensity of the
activity.
Main energy source
Intensity level
Rate of ATP production
Power production
Capacity for total ATP production
Endurance capacity
Oxygen needed
Anaerobic/aerobic
Characteristic track event
Time factor
V.
0:45
42,200
(marathon)
ATP-PC
LACTIC ACID
OXYGEN
OXYGEN
ATP; phosphocreatine
Highest
Highest
Highest
Lowest
Lowest
No
Anaerobic
100-meter dash
1–10 secs
Carbohydrate
High
High
High
Low
Low
No
Anaerobic
400–800 meters
10–120 secs
Carbohydrate
Lower
Lower
Lower
High
High
Yes
Aerobic
5000-meter (5 km) run
5 mins or more
Fat
Lowest
Lowest
Lowest
Highest
Highest
Yes
Aerobic
Ultradistance
Hours
The Predominant Energy Systems for Selected Sports
% ATP Contribution by Energy System
Sport/Activity
ATP-PC
Anaerobic
Glycolysis
Aerobic
Baseball
Basketball
Field Hockey
Football
Golf (swing)
Gymnastics
Ice Hockey:
Forwards/defense
Goalie
Rowing
Soccer:
Goalie/wings/strikers
Halfbacks
80
80
60
90
100
90
15
10
20
10
—
10
5
10
20
—
—
—
80
95
20
20
5
30
—
—
50
80
60
20
20
—
20
33
% ATP Contribution by Energy System
Sport/Activity
Swimming:
Diving
50 meters
100 meters
200 meters
400 meters
1,500 meters
Tennis
Track and Field:
100/200 meters
Field events
400 meters
800 meters
1,500 meters
5,000 meters
Marathon
Volleyball
Wrestling
ATP-PC
Anaerobic
Glycolysis
Aerobic
98
95
80
30
20
10
70
2
5
15
65
40
20
20
—
—
—
5
40
70
10
98
90
40
10
5
2
—
90
45
2
10
55
60
35
28
2
10
55
—
—
5
30
60
70
98
—
—
From E.L. Fox and D.K. Mathews, Interval Training: Conditioning for Sports and General
Fitness. Copyright ©1974 Saunders College Publishing, Orlando, FL. Reprinted by permission
of the author.
VI.
Fatigue—the inability to produce or expend energy at a give intensity.
A.
ATP-PC system and fatigue
ATP ———— ADP + Pi
PCr ———— Pi + Cr
 in substrate
B.
Anaerobic glycolysis and fatigue
C6H12O6 ————— 2C3H6O3 (lactic acid)
 Heat
 pH
 in substrate
 H2O
 Alkaline reserve (NaHCO3)
C.
Aerobic systems and fatigue
CHO
Fats

——— aerobic systems  CO2 + H2O
 substrate (CHO)
VII.
 Heat
 H2O
Beneficial Effects of Warm-up
A.
Breakdown of oxyhemoglobin for delivery of oxygen to working muscle is increased
B.
Release of oxygen from myoglobin is increased
C.
Activation energy for cellular metabolic chemical reactions is lowered
D.
Muscle viscosity is reduced, improving mechanical efficiency
E.
Nervous impulses travel faster and sensitivity of nerve receptors are augmented
34
F.
G.
H.
I.
J.
Blood flow to working muscle is increased
Cardiovascular (heart and blood vessels) response to sudden strenuous exercise is improved
Number of injuries related to muscle, tendons, ligaments, and other connective tissue may be
reduced
Best type of warm-up is that which is closely related to the activity you plan to engage in
Field tests of warm-up and cool-down
1.
Warm-up = onset of sweating
2.
Cool-down = heart rate below 100 beats per minute
OXYGEN UPTAKE
I.
Oxygen uptake—the ability to use oxygen at the cellular level. This is an excellent indicator of
aerobic capacity.
A.
Ways to determine oxygen uptake
1.
Liters of oxygen per minute = 4 liter O2/min
2.
Milliliters of oxygen per kilogram of body weight per minute
a.
Weight = 154 lbs ÷ 2.2 = 70 kg
b.
O2 uptake = 4.2 liters/min = 4200 ml/min
c.
4200 ÷ 70 = 60 ml O2/kg body wt/min
B.
Largest maximum oxygen uptake
1.
7.5 liters O2/min
2.
94 ml O2/kg/min
C.
Effects of increased body fat
1.
Weight = 70 kg (154 lbs) MaxO2 uptake = 4.2 liters/min – 4200 ÷ 70 = 60 mlO2/kg/min
2.
Increase of 2 kg of fat = 4.4 lbs 70 kg + 2 kg = 72 kg – 4200 ÷ 72 = 58.3 mlO2/kg/min
3.
4.
5.
D.
Difference = 1.7 mlO2/kg/min = 3% decrease in max O2 uptake
This loss in max O2 uptake might add 5 minutes on to a person’s marathon time
Losses in muscle mass and gains in body fat can be combated with proper conditioning
programs
The use of one liter of O2 or the equivalent of one liter of O2 yields approximately 5 kcals of
energy.
Average Values for Maximal Oxygen Uptake for Men and Women of Various Ages
Men
Age Group (Years)
VO2 (l/min)
VO2 (ml/kg/min)
20–29
30–39
40–49
50–59
3.10–3.39
44–51
2.80–3.39
40–47
2.50–3.09
36–43
60–69
2.30–2.79 1.90–2.49
32–39
27–35
Women
Age Group (Years)
VO2 (l/min)
VO2 (ml/kg/min)
20–29
30–39
40–49
50–65
2.00–2.49
35–43
1.90–2.39
34–41
1.80–2.29
32–40
1.60–2.09
29–36
35
Maximum Oxygen Uptake (l/min)
Relationship Between VO2 Max & Age for Men & Women,
Expressed in l/min.
4
3
2
1
0
0
10
20
30
40
50
60
70
Maximum Oxygen Uptake (ml/kg/min)
Age (years)
Relationship Between VO2 Max & Age for Men & Women,
Expressed in ml/kg/min.
70
60
50
40
30
20
0
10
20
30
40
50
60
70
Age (years)
E.
Factors that influence aerobic capacity
1.
O2 Uptake—Highly trained adult athletes can maintain a work level representing
100% of the oxygen uptake capacity for about 15 minutes.
36
F.
Methods to estimate maximum oxygen uptake
1.
VO2 max = .21 (age x sex) - 0.84 (BMI) - 8.41 (MT) + 0.34 (MT2) + 108.94
Age = age in years
BMI = body mass index
Sex = 0 for female, 1 for male
MT = mile time in minutes (must change seconds to hundredths of minutes)
Example:
Age = 15 yrs; Sex = female; BMI = 24.3; MT = 8.75 mins; VO2max =
0.21 (15 x 0) - 0.84 (24.3) - 8.41 (8.75) + 0.34 (8.752) + 108.94 =
40.97 ml O2/kg/min.
Body mass index.
Copyright 1993. CSPI. Reprinted/Adapted from Nutrition Action
Healthletter (1875 Connecticut Avenue NW, Suite 300, Washington, DC
20009-5728. $24.000 for 10 issues).
Above 30:
Below 20:
A person may be over fat and this 20 to 25:
makes them susceptible to
diabetes, heart disease, cancer,
and other health complications.
26 to 30:
You may be fine if you’re in
good physical condition and do
not have a disease that might be
causing you to be underweight.
This is a good value. People in this group
live longer and are at a decreased risk for
various diseases.
A person is overweight and has an increased
risk of developing high levels of cholesterol,
blood pressure, blood glucose, and blood
insulin.
37
2.
Predicted aerobic fitness classification
Age in Years
Men’s Aerobics Fitness Classification (Predicted)
Category
I. Very Poor
II. Poor
Measure
13–19
20–29
30–39
40–49
50–59
60+
O2 uptake (ml/kg/min)
<35.0
<33.0
<31.5
<30.2
<26.1
<20.5
*T.M. time (min:sec)
<14:30
<12:50
<12:00
<11:00
<9:00
<5:30
12-min. dist. (mi)
<1.30
<1.22
<1.18
<1.14
<1.03
<.87
1.5-mile time (min:sec)
>15:31
>16:01
>16:31
>17:31
>19:01
>20:01
35.0–38.3
33.0–36.4
31.5–35.4
30.2–33.5
26.1–30.9
20.5–26.0
14:30–16:44
12:50–15:29
12:00–14:59
11:00–13:29
9:00–11:29
5:30–8:49
1.30–1.37
1.22–1.31
1.18–1.30
1.14–1.24
1.03–1.16
.87–1.02
12:11–15:30
14:01–16:00
14:44–16:30
15:36–17:30
17:01–19:00
19:01–20:00
38.4–45.1
36.5–42.4
35.5–40.9
33.6–38.9
31.0–35.7
26.1–32.2
16:45–21:07
15:30–18:59
15:00–17:59
13:30–16:59
11:30–14:59
8:50–12:29
1.38–1.56
1.32–1.49
1.31–1.45
1.25–1.39
1.17–1.30
1.03–1.20
10:49–12:10
12:01–14:00
12:31–14:45
13:01–15:35
14:31–17:00
16:16–19:00
45.2–50.9
42.5–46.4
41.0–44.9
49.0–43.7
35.8–40.9
32.2–36.4
21:08–24:44
19:00–21:59
18:00–20:59
17:00–19:59
15:00–17:59
12:30–15:44
12-min. dist. (mi)
1.57–1.72
1.50–1.64
1.46–1.56
1.40–1.53
1.31–1.44
1.21–1.32
9:41–10:48
10:46–12:00
11:01–12:30
11:31–13:00
12:31–14:30
14:00–16:15
51.0–55.9
46.5–52.4
45.0–49.4
43.8–48.0
41.0–45.3
36.5–44.2
24:45–27:47
22:00–24:59
21:00–23:59
20:00–22:59
18:00–21:14
15:45–20:37
12-min. dist. (mi)
1.73–1.86
1.65–1.76
1.57–1.69
1.54–1.65
1.45–1.58
1.33–1.55
8:37–9:40
9:45–10:45
10:00–11:00
10:30–11:30
11:00–12:30
11:15–13:59
>56.0
>52.5
>49.5
>48.1
>45.4
>44.3
>27:48
>25:00
>24:00
>23:00
>21:15
>20:30
12-min. dist. (mi)
>1.87
>1.77
>1.70
>1.66
>1.59
>1.56
<8.37
<9:45
<10:00
<10:30
<11:00
<11:15
12-min. dist. (mi)
III. Fair
12-min. dist. (mi)
IV. Good
V. Excellent
VI. Superior
*Treadmill time using Balke-Ware technique.
38
Age in Years
Women’s Aerobics Fitness Classification (Predicted)
Category
I. Very Poor
II. Poor
III. Fair
Measure
13–19
20–29
30–39
40–49
50–59
60+
<25.0
<23.6
<22.8
<21.0
<20.2
<17.5
<8:30
<7:46
<7:15
<6:00
<5:38
<4:00
12-min. dist. (mi)
<1.0
<.96
<.94
<.88
<.84
<.78
>18:31
>19:01
>19:31
>20:01
>20:31
>21:01
25.0–30.9
23.6–28.9
22.8–26.9
21.0–24.4
20.2–22.7
17.5–20.1
8:30–11:29
7:46–10:09
7:15–9:29
6:00–7:59
5:38–6:59
4:00–5:32
12-min. dist. (mi)
1.00–1.18
.96–1.11
.95–1.05
.88–.98
.84–.93
.78–.86
18:30–16:55
19:00–18:31
19:30–19:01
20:00–19:31
20:30–20:01
21:00–20:31
31.0–34.9
29.0–32.9
27.0–31.4
24.5–28.9
22.8–26.9
20.2–24.4
11:30–13:59
10:10–12:59
9:30–11:59
8:00–10:59
7:00–9:29
5:33–7:59
1.19–1.29
1.12–1.22
1.06–1.18
.99–1.11
.94–1.05
.87–.98
16:54–14:31
18:30–15:55
19:00–16:31
19:30–17:31
20:00–19:01
20:30–19:31
35.0–38.9
33.0–36.9
31.5–35.6
29.0–32.8
27.0–31.4
24.5–30.2
14:00–17:29
13:00–15:59
12:00–14:59
11:00–12:59
9:30–11:59
8:00–10:59
1.30–1.43
1.23–1.34
1.19–1.29
1.12–1.24
1.06–1.18
.99–1.09
14:30–12:30
15:54–13.31
16:30–14:31
17:30–15:56
19:00–16:31
19:30–17:31
39.0–41.9
37.0–40.9
35.7–40.0
32.9–36.9
31.5–35.7
30.3–31.4
17:30–18:59
16:00–17:59
15:00–16:59
13:00–15:59
12:00–14:59
11:00–11:59
1.44–1.51
1.35–1.45
1.30–1.39
1.25–1.34
1.19–1.30
1.10–1.18
12:29–11:50
13:30–12:30
14:30–13:00
15:55–13:45
16:30–14:30
17:30–16:30
>42.0
>41.0
>40.1
>37.0
>35.8
>31.5
>19:00
>18:00
>17:00
>16:00
>15:00
>12:00
12-min. dist. (mi)
>1.52
>1.46
>1.40
>1.35
>1.31
>1.19
<11.50
<12:30
<13:00
<13:45
<14:30
<16:30
12-min. dist. (mi)
IV. Good
12-min. dist. (mi)
O2 uptake (ml/kg/min
V. Excellent
12-min. dist. (mi)
VI. Superior
*Treadmill time using Balke-Ware technique.
G.
H.
Relationship between percentage of maximum oxygen uptake and percentage of maximum
heart rate.
Percent Max H.R.
Percent Max Oxygen Uptake
50
~22
55
~28
60
~42
65
~48
70
~52
75
~60
80
~70
85
~78
90
~85
95–100
~93
Methods to estimate maximum heart rate
1.
220 - age = MHR
2.
208 - (0.7 x age) = MHR
3.
Obese: 200 - (0.5 x age) = MHR
39
I.
Classification of physical work
Metabolic Rate
Classification of
Work
1. Light
a. Mild
Heart Rate
(Beats per
Minute)
VO2
(liters/ VO2 (ml/kgminute)
min)
METS
Ventilation
Volume
Rate
Heat
(liters/ (breaths/
(kcal/minute) minute) minute)
R
Lactic Acid in
Multiples of
Resting Value
Length of Time
Work Can Be
Sustained
<100
<0.75
<10.5
<3
<4.0
<20
<14
0.85
Normal
Indefinite
<120
<1.50
<21.0
<6
<7.5
<35
<15
0.85
Within normal
limits
8 hours daily on the
job
<140
<2.0
<28.0
<8
<10.0
<50
<16
0.9
1.5 x
8 hours daily for
few weeks (seasonal
work, military
maneuvers, etc.)
<160
<2.5
<35.0
<10
<12.5
<60
<20
0.95
2.0 x
4 hours two or three
times a week for a
few weeks (special
physical training)
<180
<3.0
<42.0
<12
<15.0
<80
<25
<1.0
5–6 x
1 to 2 hours
occasionally
(usually in
competitive sports)
b. Exhausting >180
>3.0
>42.0
>15.0
>120
>30
>1.0
6 x or more
Few minutes; rarely
b. Moderate
2. Heavy
a. Optimal
b. Strenuous
3. Severe
a. Maximal
>12
Classification of Intensity of Exercise Based on 20 to 60 Minutes
of Endurance Training
Relative Intensity
CLASSIFICATION
OF INTENSITY
Very light
% HR MAX
% VO2MAX OR % HRR
RATING OF
PERCEIVED EXERTION
35%
30%
10
Light
35–59%
30–49%
10–11
Moderate
60–79%
50–74%
12–13
Heavy
80–89%
75–84%
14–15
90%
85%
16
Very Heavy
Source: M. L. Pollock & J. H. Wilmore. Exercise in Health and Disease. Philadelphia:
Saunders (1990). Reprinted by permission.
Centers for Disease Control and Prevention:
Moderate-intensity physical activity = 50–70% of maximum heart rate
Vigorous-intensity physical activity = 70–85% of maximum heart rate
40
Scales for Ratings of Perceived Exertion
ORIGINAL
RPE SCALE
6
7
8
9
10
11
12
13
14
15
16
17
18
19
NEW RATIO
RPE SCALE
Very, very
light
Very light
Fairly light
Somewhat
hard
Hard
Very hard
Very, very
hard
Source: Borg.10
J.
0
0.5
1
2
3
4
5
6
7
8
9
10
Nothing at all
Very, very weak
Very weak
Weak
Moderate
Somewhat strong
Strong
Very strong
Very, very strong
Maximal
ESTIMATING MAXIMUM HEART RATE
1. 220 - age = MHR
2. 208 - (0.7 x age) = MHR
OBESE
1. 200 - (0.5 x age) = MHR
HEART RATE RESERVE
HRR
HRmax
RHR
= HRmax - RHR
= Maximum heart rate
= Resting heart rate
MET (Metabolic Equivalent)
One MET represents the average seated,
resting energy cost of an adult.
One MET = 3.5 ml of O2 per kg per
minute or 1 kcal per kg per hour.
Steady state: oxygen uptake = oxygen demands
1. Increases in intensity and oxygen demands = as intensity doubles the oxygen demands
increase by the power of 2–4.
2. Oxygen deficit = the difference between the oxygen required during exercise and the
oxygen utilized. Indicates energy production supplied by anaerobic systems.
a. EPOC: Excess post-exercise oxygen consumption. The oxygen used during recovery to
bring systems back to a resting baseline. This is an indication of the oxygen deficit.
3. Total oxygen cost (oxygen equivalent) = oxygen utilized during activity + oxygen used to
recover from the activity (EPOC).
K. Lactate threshold
1. The point at which lactic acid entry into the blood exceeds its removal, and it has to be
buffered by sodium bicarbonate (alkaline reserve) in the plasma.
a. Buffering of lactic acid
(1) Maximum buffering capacity = about 130 grams of HL
(2) Maximum exercise = may produce 3 grams HL per second
(3) Buffering capacity = about 43 seconds of maximal work
(4) Half life of HL = 15–25 minutes
2. Also known as anaerobic threshold and onset of blood lactate accumulation (OBLA).
3. Lactic acid is always produced during exercise, but it is handled within the cells as fast as it
is produced until an increase in intensity forces the oxygen demands to increase to the point
where the lactate threshold is reached.
4. Untrained individuals: lactate threshold is reached at 50–60% maximum oxygen uptake or
about 65–73% MHR.
41
5.
Trained individuals: lactate threshold is reached at 65–80% of maximum oxygen uptake or
about 77–89% MHR. One of the largest lactate threshold reported was 90% of maximum
oxygen uptake. This individual had a great capacity to do steady state work at fairly high
intensities.
6.
Read article in appendix at end of this unit
a. Anaerobic Threshold Training, p. 66
L. Physiological factors limiting performance
1. Maximum oxygen uptake
2. Lactate threshold
3. Economy of movement
M. Increasing maximum oxygen uptake
1. Increase the muscle cell’s ability to take oxygen from the blood and increase the capability
of the aerobic energy releasing systems
a. Increase mitochondria and myoglobin
b. Increase capillarization
c. Increase cardiac output
d. Train at or just above lactate threshold
AEROBIC ENDURANCE TRAINING REDUCES THE O2
DEFICIT AT THE ONSET OF WORK
Faster Rise
No Change In Steady State
Oxygen Uptake (l/min)
2
Before Training
After Training
Faster rise in
Oxygen uptake
1
Less LA formation
Less PC depletion
0
0
1
2
3
Minutes
4
5
6
42
N. Increasing lactate threshold
1. Increase the ability of the heart and striated muscle tissue (slow twitch fibers) to clear lactic
acid from the blood
a. Increase the amount of MCT (monocarboxylate transport) which aids in the transport of
lactic acid into and out of the cell
1. MCT 1—imports lactic acid into a muscle cell (ST)
2. MCT 4—exports lactic acid from a muscle cell (FT)
b. Increase the buffering capacity of the cell and the plasma of the blood
c. Train at high intensities: 45- to 120-second intervals at close to maximum intensity
with 2- to 4-minute recoveries
O. Economy of movement
1. Strength training—this type of training has an effect on economy of movement
a. Increased strength reduces the number of muscle cells needed to exert a force and this
decreases oxygen demand
b. Increased strength reduces unnecessary body motion during movement and this
decreases oxygen demands
c. Strength training, if specific to movement, improves the coordination of muscle activity
by the nervous system and allows more propulsive force to be exerted per unit of
energy expended
MUSCLE
Muscle

Motor Units

ST(SO)
I.
FT
• FTa (FOG)
• FTx (FG)
Characteristics of Various Motor Units
A. Motor unit—a single motor neuron and all of the muscle cells innervate by the neuron. A
muscle is made up of motor units
43
B. Types of motor units
1. Fast twitch (FT) (Type II)
a. FTa; Type IIa; FOG (fast twitch oxidative glycolytic)
b. FTx; Type IIx; FG (fast twitch glycolytic)
2. Slow twitch (ST) (Type I); SO (slow twitch oxidative)
44
C. Summary of the characteristics of fast twitch and slow twitch motor units
Characteristic
NEURAL ASPECTS
Motoneuron size
Motoneuron recruitment threshold
Motor nerve conduction velocity
STRUCTURAL ASPECTS
Muscle fiber diameter
Mitochondrial density
Capillary density
Myoglobin content
ENERGY SUBSTRATE
Creatine phosphate stores
Glycogen stores
Triglyceride stores
ENZYMATIC ASPECTS
Glycolytic enzyme activity
Oxidative enzyme activity
FUNCTIONAL ASPECTS
Twitch (contraction) time
Relaxation time
Force production
Fatigue resistance
DISTRIBUTION
Endurance athletes
Sprint, explosive athletes
Other nonendurance athletes
ST
FTa
FTx
Small
Low
Slow
Large
High
Fast
Large
High
Fast
Small
High
High
High
Large
High
Medium
Medium
Large
Low
Low
Low
Low
Low
High
High
High
Medium
High
High
Low
Low
High
High
High
High
Low
Slow
Slow
Low
High
Fast
Fast
High
Low
Fast
Fast
High
Low
Medium to high (±40%?)
High (>60%?)
Medium to low (<40%?) Medium to high (±30%?)
Medium with variable distribution
Medium (±50%)
Low (±10%)
High (±30%?)
D. Typical motor unit composition in elite athletes representing different sports and average or
nonathletes
E.
Sport
% Slow-Twitch Fibers
% Fast-Twitch Fibers
Distance running
Track sprinters
Weight lifting
Shot putters
Nonathletes (average individuals)
60–90
25–45
45–55
25–40
47–53
10–40
55–75
45–55
60–75
47–53
The ramp effect and the recruitment of various motor units
1. Force development
45
F.
The ramp-like recruitment of muscle fibers in varied levels of muscular effort.
Whereas light force requirements only use the slow-twitch fibers, heavy loads on the muscle
will result in the recruitment of all three types of muscle fibers.
2. Motor unit utilization and oxygen demands
a. ST = up to about 40% max O2 uptake = up to 60% MHR
b. FTa = 40–75% max O2 uptake = 60–80% MHR
c. FTx = about 75% max O2 uptake = 82% MHR
Recruitment of ST and FT motor units during sports performance
1. Although both FT and ST units are probably called upon during most sports activities, ST
units are preferentially used during performance of aerobic endurance activities.
Conversely, FT fibers are preferentially recruited during the performance of sprint-like
activities.
2. One of the most important applications of this information, regarding sports, is in the area of
training. It is clear that in order to increase the metabolic potential of FT fibers, the activity
during training must consist of high-intensity exercise. This will ensure that the FT fibers
will be active during the training sessions. By the same token, to increase the metabolic
potential of ST fibers, the training activity must consist of lower-intensity, longer-duration
exercises. Under these conditions, ST fibers will be used preferentially during the training
sessions.
3. At any given velocity of movement, the peak power generated is greater in muscle that
contains a high percentage of fast-twitch fibers when compared to muscle with a high
percentage of slow-twitch fibers. This difference is due to the biochemical differences
between fast- and slow-twitch fibers. Again, athletes who possess a high percentage of fasttwitch fibers can generate more power than athletes with predominately slow-twitch fibers.
4. The peak power generated by any muscle increases with increasing velocities of movement
up to a movement speed of 200–400 degrees/second. The reason for the plateau of power
output with increasing movement speed is because muscular force decreases with increasing
speed of movement. Therefore, with any given muscle group there is an optimum speed of
movement that will elicit the greatest power output.
5. Determining Muscle Motor Unit Type
a. Establish 1RM for specific lift
b. Perform as many repetitions as possible at 80% of 1RM
1. If you can only perform a few reps (less than 7), then the muscle group is likely
composed of more than 50% FT motor units.
2. If you can perform many reps (more than 12), then the muscle group likely has
more than 50% ST motor units
3. If you can only perform between 7 and 12 reps, then the muscle group probably
has an equal proportion of ST and FT motor units
Age and Sex
Low % FT fibers
Males
Females
Under 13 in.
Under 6 in.
Males
Females
Under 15 in.
Under 8 in.
FT = fast-twitch muscle fibers
Average (50%) % FT fibers
UNDER 14
13–18 in.
6–10 in.
OVER 14
15–21 in.
8–13 in.
High % FT fibers
Over 18 in.
Over 10 in.
Over 21 in.
Over 13 in.
46
RECOVERY PERIOD
I.
Fast Phase
A. Regeneration of oxyhemoglobin and oxymyoglobin
Total ATP
Required
Oxygen System
O2-Myoglobin
Phosphagen Stores
Lactic Acid System
0
0.04
0.08
0.12
0.16
0.2
0.24
ATP, Moles
During intermittent exercise, the oxygen bound to myoglobin is replenished during rest
periods and reused during subsequent work periods. Of the total ATP required during the
particular exercise, nearly 20% was supplied by the oxygen bound to myoglobin. (Based on data
from Essén and co-workers, 1977.)
B. AVO2 concentration to resting values
47
C. Renewal of ATP and PC
Fast Phase
Aerobic Systems
Exercise
II.
ATP-PC System
ATP
Recovery
Pi + Cr
PCr
ADP + Pi
ATP
Slow Phase
A. Reduce body temperature—accounts for 60–70% of slow phase oxygen after exercise at 50–80%
of maximum oxygen uptake
B. Restore intra- and extra-cellular concentrations
C. Restore hormone levels
D. Restore lactic acid level = restore anaerobic glycolysis
E. Metabolism of lactic acid in recovery period
1. Utilized as a substrate in aerobic systems in muscle tissue (cardiac and striated (ST) muscle)
70%
2. Converted to glucose and then to glycogen in the liver and FT motor units 20%
48
RECOVERY PERIOD
Slow Phase
Plasma = NaL + H2CO3
C3H6O3 + NaHCO3
ST and Cardiac Muscle
Liver and FT Muscle
70%
C3H6O3
ATP to run this
system comes from
aerobic systems
3.
4.
5.
F.
2H + C3H4O3
2H + acetyl CoA
8H
Krebs Cycle
ETS
ATP
20%
2C3H6O3
C6H12O6
ATP to run this
system comes from
aerobic systems
Converted to amino acids in liver 10%
Some may be eliminated by the kidneys
Light exercise (32% of maximum O2 uptake or about 53% MHR) increases lactic acid
removal
Restoration of liver and muscle glycogen stores
1. A high-intensity exercise bout uses carbohydrate at a very high rate, but the total use is
limited due to the brief duration that the exercise can be maintained. Reduction of muscle
glycogen during a typical resistance exercise bout or a single 30-second sprint is likely to be
in the range of 25–35% of the total glycogen store in the active muscles, whereas repeated
sprints will cause a greater drain on glycogen.
2. Muscle glycogen is depleted more rapidly from Type II (fast) than from Type I (slow) fibers
during high-intensity exercise. Thus, even when the total depletion of glycogen sampled
from a mixture of muscle fibers may be quite modest, extensive glycogen use in some
muscle fibers as well as selective depletion of glycogen from specific cellular compartments
may precipitate fatigue when bodily stores of carbohydrate are low.
3. Performance of a single sprint or of repeated sprints is usually superior after a highcarbohydrate compared to a low-carbohydrate diet.
4. The benefit of high-carbohydrate diets versus moderate-carbohydrate diets for performance
of high-intensity exercise has not been clearly shown.
5. Wise coaches should allow three to four days and insist on a high carbohydrate diet for full
recovery of the glycogen stores in their endurance athletes. If several days are not possible,
then at least 10 hours should be allowed.
6. For nonendurance athletes, only one to two days and a normal amount of dietary
carbohydrate should be sufficient for full recovery of muscle glycogen after high-intensity,
intermittent exercise. If this is not possible, then allow at least five hours.
7. With intermittent exercise, some glycogen resynthesis can be expected within the first two
hours of recovery (some will occur within just thirty minutes) even in the absence of food
intake. This should help delay progressive glycogen depletion resulting from repeated
performance over a short period of time.
49
G. Recovery times following exhaustive exercise
Fast
Phase
Slow
Phase
Recovery Process
• Restoration of O2 stores
• Restoration of muscle phosphagen
stores (ATP and PC)
– Half life = 20–30 secs
• Repayment of fast part of EPOC
Recovery Time
Minimum Maximum
Trained
Untrained
10–15 secs 1 min
2 mins
5 mins
3 mins
5 mins
• Removal of lactic acid from blood
(anaerobic glycolysis)
– Half life = 15–25 mins
30 mins
1 hr
(exercise recovery)
1 hr
1 hr
(rest recovery)
• Repayment of slow part of EPOC
• Liver glycogen replenishment
• Muscle glycogen resynthesis
30 mins
1 hr
Unknown
12–24 hrs
10 hrs
46 hrs
(for continuous exercise)
5 hrs
24 hrs
(for intermittent exercise)
H. Aerobic base—it is important to realize that the anaerobic systems are recovered by using energy
released from the aerobic systems
I. Reasons for developing an aerobic base
A. Cellular changes—the increase in mitochondrial material in muscle from aerobic endurance
training results in an increase in exercise muscle mitochondrial capacity. As determined in
laboratory animals, muscle mitochondrial capacity is significantly better correlated with
running endurance than is VO2max. The increase in exercise endurance associated with an
increase in muscle mitochondrial mass is probably due to a number of factors:
1. Increased mitochondrial mass and activity provide an increased capacity to oxidize all
substrates
2. Increased mitochondrial mass specifically allows for greater fat oxidation capacity,
thereby sparing glycogen reserves
3. Increased mitochondrial mass allows for a greater clearance of lactic acid formed
during exercise. Thus, trained individuals can tolerate greater rates of glycolysis and
lactic acid production while at the same time maintaining low circulating lactic acid
levels. Lactic acid is a stressor that, among other effects, inhibits fat mobilization
4. Increased mitochondrial mass provides for a greater capacity to withstand
mitochondrial damage during exercise. Although not a great deal of research has yet
been performed on mitochondrial damage during exercise, it is apparent that oxygen
reacts in nonenzymatically mediated ways (e.g., as superoxide free radical) with
cellular membranes, including mitochondrial membranes. By increasing the
mitochondrial mass, aerobic endurance training reduces the impact of oxidative
damage. In addition, training induces an increase in the amount of enzymes (e.g.,
superoxide dismutase, SOD) that protect against oxidative damage
5. In addition to increasing the mitochondrial mass, aerobic endurance training results in
several other biochemical adaptations within muscle. These adaptations function to
improve the supply of O2 and substrates to mitochondria
50
6.
Training greatly increases the concentration of myoglobin in the cytoplasm of cells.
This adaptation facilitates the movement of O2 from areas of higher oxygen partial
pressure (PO2) within and near capillaries to areas of lower PO2 deep within the cell
7. Training increases the sensitivity of muscle to insulin. Working muscle of trained
individuals can therefore take up glucose from the blood even though glucose and
insulin levels may be low
8. Training increases the amount of the glycolytic enzyme hexokinase in skeletal muscle.
Selectively increasing the amount of hexokinase, a large fraction of which is bound to
the outer mitochondrial membrane, allows for greater utilization of blood glucose and
lesser use of muscle glycogen during exercise. This adaptation is possibly one of the
reasons that exercise training improves the utilization of glucose in Type 2, insulininsensitive diabetes
9. Training improves the amount of Type L hormone-sensitive lipase in muscle. This
adaptation allows for greater use of triglyceride contained in circulating lipoproteins
and intramuscular fat during exercise. Training also increases the involvement of
amino acids in the metabolic adjustments sustaining prolonged exercise. Increased
amounts of glutamate-pyruvate transaminase (GPT) allow for more pyruvate to be
converted to alanine (and less to lactate) during exercise. Consequently, glucosealanine cycle activity and blood glucose homeostasis are improved with endurance
training. And, finally, training increases the ability to use leucine and alanine as
oxidizable substrates during exercise
10. Training may increase mitochondrial content in skeletal muscles by about 100 percent
B. Cardiovascular changes—no discussion of the aerobic adaptations to aerobic endurance training
can be complete without mentioning that training increases the volume of blood that can be
ejected from the heart in each beat. Endurance training therefore improves stroke volume,
cardiac output, O2 transport capacity, and VO2max. Aerobic endurance training improves the
capacity for O2 transport and VO2max by 10 to 30 percent
C. Connective tissue changes—aerobic endurance training may affect the structure of connective
tissue and thus decrease the chance of injury to connective tissue
51
APPENDIX
1. Sports Nutrition
2. Anaerobic Threshold Training
52
Mosby-Year Book
January 1991
Sports Nutrition
by
David R. Lamb
Gordon M. Wardlaw
Athletes invest a lot of time
and effort in training. Because
they are often seeking ways to
modify their diets to improve
their performances, athletes
make easy targets for
nutritional “quacks.” Most
athletes don't want to miss out
on any advantages, whether
real or perceived, that might
give them the winning edge.
Proper diet choices are a key
ingredient to top-notch
performance.5 The goal of this
newsletter is to lead you
through those choices. We
begin with various metabolic
changes that accompany
exercise and then use this
backdrop to frame diet
recommendations.
Energy for the Cell
Muscles primarily burn carbohydrate and fat for energy. Little protein fuel is used.
Some carbohydrate fuel is used during all types of exercise, but especially when
energy needs for movement exceed the ability to produce energy by burning fat. The
overall goal of any fuel use—carbohydrate, fat or protein—is to make adenosine
triphosphate (ATP).
Adenosine triphosphate is the ,immediate source of energy for body functions.
This includes locomotion.16 A resting muscle cell has a small amount of ATP that
can be split into adenosine diphosphate (ADP) plus a phosphate group (abbreviated
as P) (Figure 1).
This splitting of ATP simultaneously releases energy that can be used to make
the muscle contract. If no resupply of ATP were possible, this stored ATP could
53
keep the muscle working maximally for only about 1 second. Fortunately, there are several types of chemical
compounds—phosphocreatine, carbohydrates, fats, and proteins–that can be broken down to release enough energy to
cause ADP and P to recombine, thereby replenishing ATP stores.12 Thus, cells constantly recycle ADP plus P to form ATP
and then reverse the cycle, reusing ATP
components over and over again.
Definitions
Phosphocreatine is the
First Line of Defense for
Resupplying ATP in
Muscles
Adenosine
triphosphate
(ADP)
The main energy source for cells. Energy is released
when a high energy phosphate bond is broken. This form
of energy is used for muscle contractions.
Aerobic
Using oxygen. Aerobic activities use large muscle
groups at moderate intensities. This permits the body to
use oxygen to supply energy and to maintain a steady
rate for more than a few minutes.
Anaerobic
Not using oxygen. Anaerobic activities use muscle
accumulate in the contracting muscle from
groups at high intensities that exceed the body's capacity ATP being broken down for energy, an
to supply energy using only oxygen-requiring pathways. enzyme is activated to split phosphocreatine
The instant that ADP and P begin to
(PCr) into phosphate (P) plus creatine (Cr).
The P immediately combines with ADP to
resupply ATP; thus, PCr + ADP 6 Cr + ATP.
If no other source of ATP resupply were
available, PCr could probably maintain
Carnitine
A substance responsible for transporting fats into the
maximal muscle contraction for about 10
mitochondria for energy production. Body cells make
seconds. [Actually, because other ATP sources
this substance.
kick in, PCr is a major source of energy for all
Citric acid cycle
A final common metabolic pathway for fats, proteins,
events lasting up to about 1 minute.]12
and carbohydrates. Carbon dioxide and water are
The main advantage of PCr is that it can be
produced, as well as substances that can be used to
activated instantly and can replenish ATP at
synthesize ATP in the electron transport system.
rates fast enough to meet the energy demands
Cytosol
Fluid portion inside a cell that contains cell bodies such of the fastest and most powerful sports events,
including all jumping, lifting, throwing, and
as mitochondria. Also called cytoplasm.
sprinting actions. The disadvantage of PCr is
that there is not enough PCr stored in the
Electrolyte
Minerals like sodium, chloride, and potassium that can
conduct electrical currents when dissolved in water .
muscles to sustain this high rate of ATP
resupply for more than a few minutes. Many
Electron transport A metabolic pathway in which substances from the citric attempts have been made over the years to
system
acid cycle enter to yield ATP. This system requires
improve the muscle ATP and PCr stores by
oxygen.
dietary means, but these attempts have failed.
Carbohydrate
loading
A dietary scheme emphasizing high amounts of
carbohydrate to increase muscle glycogen stores before
long endurance events.
Ergogenic aid
A physical, mechanical, nutritional, psychological or
pharmacological substance or treatment that directly
improves exercise performance.
Glycolysis
A metabolic pathway that converts glucose to pyruvate
(or lactate) to produce energy in the form ofATP.
Lactate (lactic
acid)
The end product of the metabolism of glucose
(glycolysis) for the anaerobic production of energy.
Mitochondria
Rod-like organelles inside cells that contain the citric
acid cycle and electron transport system. This is the
major site for ATP production in a cell. Muscle cells
contain numerous mitochondria.
VO2 max
Maximum volume of oxygen consumed per unit of time
during exercise.
Releasing the Energy in
Carbohydrate Begins
with Glycolysis
The most useful form of carbohydrate fuel is a
simple sugar called glucose, which is available
to all cells from the bloodstream. The
breakdown of liver glycogen (a storage form
of glucose) helps maintain blood glucose
levels. In muscles, breakdown of glycogen
stored there helps fuel muscle cells. The
catabolic pathway that breaks down glucose is
called glycolysis (“glyco” means sugar and
“lysis” means breakdown). As a result of
54
glycolysis, the 6-carbon glucose splits into two units of pyruvic acid (pyruvate), a 3-carbon compound.13 (See an
introductory physiology or nutrition text, such as Perspectives in Nutrition by Wardlaw and Insel, to review the actual
steps in the various biochemical pathways discussed in this newsletter.) The net energy produced from breaking down
one glucose to two pyruvates equals two ATP. Although this phase of glycolysis does not do a very good job in extracting
energy from a single glucose molecule, a muscle cell can break down thousands of glucose molecules per second and thus
resupply ATP at a very high rate for a brief period.
When glucose breaks down, the resulting pyruvate follows either of two main routes. When oxygen supply is limited
(“anaerobic”) or when the exercise is intense ( e.g., running 400 meters or swimming 100 meters), the pyruvate
accumulates in the muscle and is converted to lactate (lactic acid) in the cell's cytosol (fluid portion of a
cell). This conversion of glucose to pyruvate or lactate is called anaerobic glycolysis. Carbohydrate is the only fuel that
can be used for this process.
If there is plenty of oxygen available in the muscle (aerobic state) and the exercise activity is of moderate to low
intensity (e.g., jogging or distance swimming), the bulk of the pyruvate can be shuttled to the mitochondria of the cell,
where it is further metabolized into carbon dioxide and water. This is known as aerobic glycolysis, because the breakdown
of sugar takes place with the aid of oxygen.
Anaerobic glycolysis. The advantage of anaerobic glycolysis is that, other than PCr breakdown, it is the fastest
way to resupply ATP. Anaerobic glycolysis provides most of the energy for events ranging from about 30 seconds to 2
minutes.12 The two major disadvantages of anaerobic glycolysis are (1) this high rate of ATP production cannot be
sustained for longer events, and (2) the rapid accumulation of lactate increases the acidity of the muscle so greatly that
the acid inhibits the activities of key enzymes in the glycolysis pathway; this slows anaerobic ATP production, and in turn
causes fatigue.
Aerobic glycolysis. Aerobic glycolysis supplies energy (ATP) more slowly than does anaerobic glycolysis, but
this slower rate of aerobic energy supply can be sustained for hours. Accordingly, aerobic glycolysis makes a major energy
contribution to sports events lasting anywhere from about 2 minutes to 4 or 5 hours.
Importance of Glycogen Versus Blood Glucose for Carbohydrate
Fuel
It is important to note that muscle glycogen is the preferred fuel for both anaerobic glycolysis and for aerobic glycolysis
in fairly intense activities that last for less than about 2 hours. For these activities, the depletion of glycogen stores in the
muscle can cause fatigue. Diets high in carbohydrate can be used to build up muscle glycogen stores in advance of
competition, thereby forestalling fatigue and improving performance.15
As exercise duration increases beyond about 20 to 30 minutes, blood glucose becomes increasingly important as a
fuel for glycolysis. This use of glucose from the blood can spare the glycogen in the muscle for sudden bursts of effort
that may be required, such as a sprint to the finish in a marathon race. Because it is important to maintain high
concentrations of glucose in the blood for prolonged exercise, many investigations have studied various types of
carbohydrate feedings before and during exercise in hopes of optimizing glucose supply. We will look at this issue in a
later section.
Energy Metabolism Using Fat
When fat stores in various fat deposits in the tissues are broken down for energy, one triglyceride molecule fIrst yields
three fatty acids and a glycerol. The majority of the stored energy is found in the fatty acids. The fatty acids are released
from the fat depots into the bloodstream and travel to the muscles, where they are taken into each cell's cytosol. These
fatty acids must enter the cell's mitochondria before they can be broken down. The mitochondria produce most of the ATP
supply for a cell. The fatty acids are mostly transported from the cytosol into the mitochondria using a transport system
that contains a compound called carnitine. Athletes sometimes take carnitine pills hoping it will help them burn fat faster
in exercise. But since our cells can make carnitine quite easily, carnitine supplements are of no value.18
The rate at which muscles utilize fatty acids is dependent to some extent on the concentration of fatty acids in the
blood. In other words, the more fatty acids that are released from fat depots into the blood, the more fat will be used by
the muscles. In attempts to utilize more fat during prolonged exercise and thereby spare muscle glycogen stores, athletes
55
have attempted to raise their blood concentrations of fatty acids by eating high fat diets and by consuming caffeinated
beverages. Caffeine sometimes increases fatty. acid release from the fat depots.17
Fat is ultimately not a very useful fuel for intense, brief exercise, but it becomes progressively more important as an
energy source as exercise becomes increasingly prolonged, especially when it remains at a low or moderate rate. The
reason is that some of the steps in fat utilization simply cannot occur fast enough to meet the ATP demands of short
duration, high intensity exercise. If fat were the only available fuel, we would be unable to carry out exercise more intense
than a fast walk or jog; high-caliber sports events would be out of the question. The advantage of fat is that it provides
tremendous stores of energy in a relatively lightweight form. For a given weight of fuel, fat supplies more than twice as
much energy as carbohydrate. For very lengthy activities, such as a triathalon, ultramarathon, manual labor in a foundry,
or even sitting at a desk for 8 hours a day, fat may supply 70% to 90% of the energy required. For short events such as
a 100 meter sprint or even a 1500-meter race, the contribution of fat used to resupply ATP is minimal. Recall that the only
anaerobic fuel we eat is carbohydrate; aerobic activity uses all three energy sources, i.e., carbohydrate, fat, and protein.
Does This Mean We Use Protein to Fuel Activity?
Protein can be used for fueling muscles, but in most circumstances protein contributes only about 6% to 7% to the body's
general energy requirements. This is also true for the typical energy needs of exercising muscles. However, proteins can
contribute significantly to energy needs in endurance exercise, perhaps as much as 10% to 15%, especially as carbohydrate
stores in the muscle are exhausted.14 Contrary to what many athletes believe, protein is used less for fuel in resistance types
of exercise, i.e., weight lifting, than for endurance exercise such as running. The primary fuels for weight lifting are
creatine phosphate and carbohydrate.
The Body’s Response to Exercise
We have discussed how muscle cells obtain the ATP energy needed to do work. Let's now focus on how muscles and
related organs adapt to an increased workload.
Training—the Body Adapts to the Demand
Repeated aerobic exercise produces beneficial changes in the heart and blood vessels that are responsible for delivering
oxygen to the mitochondria of the muscles. Because it uses more oxygen, the body responds to training by producing
more red blood cells and total blood volume. The heart, a muscle itself, enlarges and strengthens. Each contraction empties
the heart's chambers more efficiently. Now more blood is pumped with each beat. As exercise increases the heart's
efficiency, its rate of beating at rest and during submaximal exercise is lower. This is an index of fitness—a lower heart
rate is seen as fitness increases. In addition, oxygen can be delivered more easily through the blood vessels of the muscles
to the mitochondria because the number of capillaries in the muscles increases after exercise training.6
After a period of aerobic training, muscle cells contain more and larger mitochondria. The muscles can then more
efficiently fuel themselves from fatty acid stores as these changes enable muscle cells to produce more ATP using oxygenrequiring pathways. This includes the pathway used to burn fat for fuel. These changes in mitochondrial function allow
for greater intensity during aerobic exercise. Furthermore, a 20% to 50% improvement in muscle glycogen stores allows
for larger carbohydrate sources to be available for muscular work. In addition, the athlete can now train harder and longer
at an “aerobic” pace.
Exercise Your Knowledge
Plan a 600 Gram Carbohydrate Diet
Use Table 3, your imagination, and the nutrient composition charts in a nutrition textbook to design a
high carbohydrate diet from foods you like. See Table 4 for some ideas. Now consider following this
diet for 1 day. Could you follow this type of diet for months while training for a marathon?
56
Measuring Exercise
Capacity
There is more oxygen in the air we inhale than
in the air we breathe out. Oxygen taken up by
the mitochondria to help produce ATP energy
accounts for this difference. The amount of
oxygen consumed by the mitochondria of the
body tissues is directly related to the ATP
requirement during exercise. Every atom of
oxygen consumed results in the production of
2 to 3 ATP molecules in the electron transport
system of the mitochondria.16 Thus, oxygen
consumption indicates how hard a person is
exercising. The harder the muscles work, the
more oxygen they demand. The more
physically fit a person is, the more work the
muscles and body can do, and the more oxygen
the person can consume. The maximum
volume of oxygen one can consume (VO2
max) is calculated by measuring oxygen
consumption while exercising, say running on
a treadmill. The treadmill speed and/or grade is
gradually increased until the subject becomes
fatigued. The point right before total
exhaustion is VO2 max.12
This is the most oxygen that one can use
(Figure 2). While each person's VO2 max is
unique, it can usually improve 15% to 20% or
even more with exercise training.
When discussing an exercise intensity, it is usually best to express that intensity as a percentage of VO2 max. Low
intensities (fast walk) require approximately 30% to 50% of VO2 max; moderate intensities (fast jog) require 50% to 65%
VO2 max; high intensities (3 hour marathon pace) use 70% to 80% VO2 max; and very high intensities (sprints) use 85150% of VO2 max. [The extra 50% is accounted for by the anaerobic production of ATP in PCr breakdown and in
anaerobic glycolysis.]
Fuel Use in Exercise—A Closer Look
The fuel used for a specific workload is determined by the intensity (portion of VO2 max used) and duration of exercise.
The availability of certain energy-yielding pathways in a cell—notably the citric acid cycle and electron transport
system—depends on the work-load and how much work has been done already (Table 1). Because these concepts are
highly complex, we will only summarize them briefly.
Rest and low level workloads. Muscle cells—either resting or during low workloads such as a brisk
walk—primarily burn fat for fuel because the supply of ATP generated from fat metabolism easily can sustain that
workload. Fuel use is about 70% to 90% fat; the rest comes mostly from carbohydrate in the mitochondria using the citric
acid cycle and electron transport system. Also, while a muscle cell is busy making ATP using fat energy, it cannot easily
make ATP using glucose energy; high concentrations of A TP and other substances produced during fat metabolism in
the cell inhibit important enzymes used in glycolysis.13 On the other hand, there is no such inhibition for use of the citric
acid cycle and electron transport system. This tips the balance toward using fat to form ATP energy.
57
Brief and maximally intense exercise. Intense exercise, such as running 200-meter sprints, requires maximum
effort and cannot be sustained. In fact, this exercise is so intense that it may last for no more than 30 seconds. For such
workloads muscles use PCr and some anaerobic glycolysis. During short bursts of maximally intense work (up to about
10 seconds), the supply of PCr is depleted rapidly from muscle tissue as it reforms ATP. The PCr system is also used as
muscle contractions begin after a rest to reinitiate activity. However, in prolonged exercise at moderate intensity, PCr is
not as critical because other cell pathways are available for ATP replenishment.
Moderately intense exercise. When someone exercises hard and sustains it for more than a few minutes-for
example, running a 6-minute mile-fat metabolism via the citric acid cycle and electron transport system cannot keep pace
with the cell's ATP demands. Both anaerobic and aerobic glycolysis must kick in to help. This is partly because the
electron transport system in each mitochondrion takes a few minutes to shift into high gear. That being the case, the ATP
concentration at the start of exercise in muscle cells drops, and ADP concentration in muscle cells increases. The PCr
system kicks in, but fades fast. Now the low ATP concentration in the muscle cells allows important enzymes in the
glycolytic process to speed up. Glycogen in the muscle then breaks down into glucose, which undergoes glycolysis to form
pyruvate. Carbohydrate ends up supplying 80% to 90% of the fuel used. Much of this pyruvate forms lactate.
Because so little ATP energy is produced for each glucose molecule in anaerobic glycolysis, this type of glycolysis
must proceed very rapidly in muscle cells to be of much value. This results in the production of many lactate molecules.
These spill into the bloodstream. Cells in the heart, the liver, and less active muscles can then pick these up and use them
for fuel or convert them to other substances.13
It has long been assumed— incorrectly—that
lactate accumulation in muscle and blood always
Table 1. Energy systems for muscle cell use.
meant that muscle was anaerobic (deprived of
oxygen) during exercise. We now know that
Example of
When in use
System
lactic acid is formed and removed continuously
an exercise
and frequently at all times, even when muscles
are at rest; only the amount of total production
All types
At all times
ATP
varies.
The lactate option is most active for the first
Shotput,
All exercise
Phosphocreatine
minute of exercise. After that, aerobic pathways
jumping
initially; extreme
(PCr)
kick in as well to keep up with ATP demands.
exercise thereafter
If a person starts exercising regularly four or
five times a week, he or she will experience a
200 yard
High intensity
(200 meter)
exercise, especially
(carbohydrate)
“training effect.”6 At the start the person might
run for time
lasting 30 seconds
be able to exercise for 20 minutes before tiring.
to 2 minutes
Months later exercise can be extended to an hour
before the person feels tired. During the months
Basketball,
Exercise lasting 2
Aerobic glycolysis
of training, muscle cells have produced more
swimming,
minutes to 4-5 hours;
(carbohydrate)
mitochondria and so can burn more fat. That
jogging
the higher the
means the person will produce less lactate during
intensity, the
exercise. Since lactate contributes to muscle
greater the use
fatigue, the less lactate produced, the longer the
Distance running,
Exercise lasting more
Aerobic fat
person will be able to exercise. Part of the
long distance
than
a
few
minutes;
utilization
training effect derives also from the increased
cycling
greater
amounts
aerobic efficiency of heart and muscles we
are
used
at
lower
described earlier. However, when you consider
levels of exercise
only metabolism, a very important result of
intensity
training is the increased number of mitochondria
in the muscle cells, resulting in less dependence
Endurance
Low levels during
Aerobic protein
on the lactate system for
running
all exercise;
utilization
energy production.
moderate levels in
Endurance exercise. Endurance
exercise, such as walking or cycling, often
involves moderate effort sustained over l or more
endurance exercise
when carbohydrate
fuel is lacking
Source: Authors
58
hours. Muscles can continue to metabolize fat via the citric acid cycle and electron transport system for about 60 to 80%
of energy needs at these moderate workloads, but aerobic glycolysis using carbohydrate also plays a role (about 15% to
30% ), along with protein fuel (up to 10%). However, less lactate builds up in endurance exercise than during high
intensity activities because the slower rate of pyruvate production can be handled by the oxidative processes of the
mitochondria.
As intensity increases, such as in a 3-hour marathon run at 70% VO2 max, muscles use about a 60:40 ratio of fat to
carbohydrate. When carbohydrate fuel (glycogen) in muscles is eventually used up, it is difficult to maintain the high
initial workload unless blood glucose concentrations are elevated by carbohydrate feedings. Athletes call this condition
.hitting the wall.. So, when levels of exertion meet or exceed 70% of VO2 max for more than an hour, an athlete (like a
long distance runner or cyclist) should consider increasing the amount of carbohydrate stored in muscles and blood.15 Later
we discuss how to do this.
How Much Food Energy Does An Athlete Need?
Athletes need varying amounts of food energy, depending upon the athlete's body size and the type of training or
competition being considered. A small person may need only 1700 kcalories daily to sustain normal daily activities
without losing body weight, whereas a large muscular man may need 3000 kcalories. These are only estimates. Consider
these starting points that need to be individualized by trial and error for each athlete. Kcalories required for sports training
or competition have to be added to this energy needed just to carry on normal activities. An hour of bowling, for example,
requires few kcalories in addition to those required to sustain normal daily living. On the other extreme, 12-hour
endurance bicycle races over mountains can require an additional 4000 kcalories per day. Therefore, some athletes may
need as much as 7000 kcalories daily just to maintain body weight while training, whereas others may need 1700 kcalories
or less.
How does one know if an athlete is getting enough energy from food? The first step is to estimate the athlete's body
fat percentage by measuring skinfold thicknesses, bioelectrical impedance, or using the underwater weighing technique.
If the body fat is in the desirable range, i.e., about 6% to 12% for most male athletes and 15% to 20% for most women
athletes, the next step is simply to monitor body weight changes on a daily or weekly basis. If the body weight starts to
fall, food energy should be increased; if weight rises, the athlete should be encouraged to eat less.
If the body composition test shows that the athlete is too fat, the athlete should eat about 200 to 500 fewer kcalories
per day until the desirable fat percentage is achieved. Reducing fat intake is the best approach. On the other hand, if the
athlete needs to gain weight, an additional 200 to 500 kcalories per day will eventually cause the needed weight gain.
Rapid weight loss by dehydration
Wrestlers, boxers, judo players, and oarsmen often try to lose weight so that they can be certified to compete in a lower
weight class and gain a mechanical advantage over an opponent of smaller stature. Most of the time, this weight is lost
a few hours before stepping on the scale for weight certification. Athletes can lose up to 22 pounds (10 kilograms) of body
water in one day by sitting in a sauna, by exercising in a plastic sweat suit, and/ or by taking diuretic drugs that speed
water loss from the kidneys. Losing as little as 3% of body weight by dehydration can sometimes adversely affect
endurance performance. A pattern of repeated weight loss and weight gain of more than 5% of body weight by
dehydration carries some risk of kidney malfunction or heat illness. Dehydration causes a reduction in blood volume,
increases the body temperature, and may result in heat cramps or heat exhaustion.
This habit of losing weight by dehydration is so ingrained in sports such as interscholastic and intercollegiate
wrestling, that most competitors probably go onto the wrestling mat to face an opponent who has gone through the same
misery to gain an .advantage.. If an athlete wishes to compete in a lower body weight class and has enough extra fat, that
athlete should begin a gradual, sustained reduction in food energy intake long before the competitive season starts. In so
doing, the athlete will have a presumably healthier body composition (less fat) and can avoid the potentially harmful and
certainly misery- creating effects of severe dehydration. If an athlete has no extra body fat he should be discouraged from
attempting to compete at a lower body weight class. It is important to make coaches and trainers aware of the decreased
performance and serious side effects of severe dehydration.
59
Power Food:
What Should an
Athlete Eat?
Athletic training and genetic makeup
are two very important determinants of
athletic performance. A good diet won't
substitute for either, but diet can further
enhance and maximize an athlete's
potential. More importantly, a poor diet
can certainly impair performance.4
General Principles
for Establishing the
Training Diet
Table 2: The daily food guide for adults: a summary
Nutritional Group
Servings
Major
Nutrients
Foods and Nutritional Service Sizes.*
Milk and cheese
group (emphasize
low fat choices)
2-3 ¶
Calcium
Riboflavin
Protein
Potassium
Zinc
1 cup milk
1 a oz cheese
1 cup yogurt
2 cups cottage
cheese
1 cup custard/
pudding
1½ cups ice cream
Meat, poultry
fish, and beans
group
(emphasize
low fat choices)
2
Protein
Niacin
Iron
Vitamin B-6
Zinc
Thiamin
Vitamin B-12†
2 oz cooked meat,
poultry, fish
1 cup cooked dry
beans
4 T peanut butter 2
eggs
½ –1 cup nuts
Anyone who exercises regularly,
including the dieter, needs to consume
½ Cup cooked fruit or
Fruits and
4
Vitamin A
a diet that includes moderate to high
vegetable
vegetables
Vitamin c
amounts of carbohydrates, about 55%
Folate
½ Cup juice
to 70% of total kcalories, rather than
1 whole fruit 1 small
Fiber
our typical 46%. Endurance athletes
salad
should meet the higher value. Fat
1 slice bread
4
Thiamin
Bread and cereal
intake should then fall from our typical
1 oz ready-to-eat
(consume
some
Riboflavin§
38% of total kcalories to 15% to 30%.
cereal
Iron
whole grains)
Protein then makes up the rest of the
½–¾ Cup cooked
Niacin
energy-about 10% to 15% of the total.
cereal, rice, or pasta
Magnesium‡
This yields a plate of about two-thirds
Fiber‡
carbohydrate-rich foods and one-third
Zinc‡
protein-rich foods.5 All athletes should
consume a variety of foods, adhering to
Fats, sweets, and
Foods from this group should not
the Daily Food Guide (Table 2).
alcohol
replace any from the four groups.
Numerous selections of starches and
Amounts consumed should be
fruits will help maintain adequate
determined by individual energy needs.
muscle glycogen stores, and especially
replace glycogen losses from the
previous day. Triathletes and *May be reduced for child servings ‡Whole grains, especially ¶3 if under 25
†Only in animal food choices
§If enriched
years of age
marathoners should consider eating
close to 600 grams of carbohydrates a This is a practical way to turn the RDA into food choices. One can obtain all essential nutrients by
day, and even more if necessary to eating a balanced variety of foods each day from the food groups listed here. Eat a variety of foods in
food group, and adjust servings sizes appropriately to reach and maintain desirable weight.
prevent chronic fatigue and to load the each
Athletes should mostly increase servings in breads and cereals to fuel extra needs. More fruits and
muscles and liver with glycogen. This vegetables in the diet can also boost carbohydrate intake. These are key to a good diet. Concentrated
is especially important when protein sources are found in the milk and cheese group and meat, poultry, fish, and beans group.
performing multiple training bouts in a
day. Table 3 can help plan such an intake. Table 4 provides an example of a high carbohydrate diet. One does not have
to give up any specific food. Just focus more on the best—high carbohydrate foods—and less on the rest—concentrated
fat sources.5
60
Table 3: Grams of Carbohydrate in Typical Foods
Carbohydrate Loading
For athletes who compete in events lasting
90 to 120 minutes or longer or in shorter
Starchy Vegetables, Breads, and Cereals—
events repeated in a 24 hour period, it is
15 Grams Carbohydrate per Serving
often advantageous to undertake a
One Serving:
.carbohydrate loading. regimen to
1/2 cup dry breakfast cereals
1 small baked potato
maximize muscle glycogen stores. This
1/2 cup cooked breakfast cereals 1/2 bagel
regimen includes a gradual reduction or
1/2 cup cooked grits
1/2 English muffin
.tapering. of exercise intensity and
1/3 cup cooked rice
1 slice bread
duration coupled with a gradual increase
1/2 cup cooked pasta
3/4 ounce pretzels
in dietary carbohydrate as a percentage of
1/4 cup baked beans
6 saltine crackers
energy intake.15 The procedure begins 6
1/2 cup corn
2 four-inch diameter pancakes
days before competition, with the athlete
1/2 cup beans
2 taco shells
completing a hard workout lasting about
60 minutes. Workouts for the next 4 days
Vegetables—5 Grams Carbohydrate per Serving
last about 40, 40, 20,and 20 minutes,
respectively, with exercise intensities
One Serving:
being progressively reduced each day. On
1/2 cup cooked vegetables
the final day before competition, the
1 cup raw vegetables
athlete rests. The dietary carbohydrate on
1/2 cup vegetable juice
the first 3 days of this regimen contributes
45% to 50% of energy intake, and this
Examples: carrots, green beans, broccoli, cauliflower, onions, spinach,
rises to 65% to 75% carbohydrate for the
tomatoes, vegetable juice
last 3 days leading up to competition. This
carbohydrate loading technique usually
Fruits—15 Grams Carbohydrate per Serving
increases muscle glycogen storage by
50% to 85% over usual conditions, i.e.,
One Serving:
when a typical amount of carbohydrate is
1/2 cup fresh fruit
12 cherries or grapes
consumed (45% of kcalories). The greater
1/2 cup fruit juice
1/2 grapefruit
carbohydrate stores then often result in
1/4 cup dried fruit
1 nectarine
improved athletic performance in
1 small apple
1 orange
endurance events.
4 apricots
1 peach
A potential disadvantage to
1/2 banana
1-1/4 cup watermelon
carbohydrate loading is that along with
the glycogen, some water is also stored in
Milk—12 Grams Carbohydrate per Serving
the muscles. The water adds body weight
and may cause muscle stiffness. For some
One Serving:
people, this makes carbohydrate loading
1 cup milk
an unfeasible practice. Athletes
8 ounces plain low-fat yogurt
considering carbohydrate loading should
try it once during training (and well
Sweets—15 Grams Carbohydrate per Serving (Note: Also high in fat)
before an important event) to experience
One Serving:
its effects on performance. They can then
1/2 cup slice cake
1/2 cup ice cream
determine if it is worth the effort.
2 small cookies
1/4 cup sherbet
Sports nutritionists emphasize the
3 gingersnaps
difference between a high-carbohydrate
meal and a high-carbohydrate/high-fat
Source: Adapted from Exchange Lists for Meal Planning by the American Diabetes
meal. Before endurance events, such as
Association and American Dietetic Association, 1986, Chicago: American Dietetic
marathons or triathalons, some athletes
Association.
attempt carbohydrate loading by eating
potato chips, french fries, banana cream
pie, and pastries. These foods do contain carbohydrate, but they also contain a lot of fat. Better food choices are pasta,
rice, potatoes, bread and many breakfast cereals. Sports drinks designed for carbohydrate loading can also help. Following
61
a moderate fiber intake during the final day is a good precaution to reduce the chances of bloating and intestinal gas during
the next day's event.
Vitamins and Minerals
Athletes usually consume many kcalories, and so they tend to consume plenty of vitamins and minerals. The B- vitamins
and minerals such as iron and copper are especially needed to support energy metabolism. If a low-energy intake—less
than 1200 kcalories—is needed, athletes should pay very close attention to their vitamin and mineral intake. A focus on
nutrient-dense foods, such as lowfat milk, broccoli, tomatoes, oranges, strawberries, whole grains, lean beef, kidney beans,
turkey, fish, and chicken is a good idea. Vitamin and mineral supplements also can be used. Vitamin and mineral intakes
greatly exceeding the Recommended Dietary Allowances (RDA) are not needed. Note that vitamin and mineral
supplements supply no known ergogenic (work-producing) benefit. They only benefit the body when a medicallydiagnosed deficiency exists!
Iron. Athletes, especially female and adolescent athletes, should focus special attention on iron intake. Iron losses
in sweat, increased iron requirements for the enhanced red blood cell production associated with athletic fitness, footstrike
destruction of red blood cells, and iron loss during menstruation deplete a woman's iron stores. When this iron is not
replenished, it can occasionally lead to iron-deficiency anemia and markedly impaired endurance performance. Although
true anemia (depressed blood hemoglobin concentration) is quite rare among athletes, it is a good idea, especially for adult
women athletes, to have the blood hemoglobin levels checked regularly and to increase dietary iron intake. Vegetarian
female athletes should be especially careful to monitor iron status. If blood iron levels are consistently low, the use of iron
supplements by an athlete may be advisable. Iron supplements can improve athletic performance if the athlete is truly
anemic, but they have no effect when the athlete simply has low blood levels of iron that have not resulted in anemia.
Calcium. Athletes, especially women who are attempting to lose weight by restricting their intake of dairy products,
can have marginal or deficient dietary intakes of calcium. This practice does not contribute to optimum bone health. Of
still greater concern are women athletes who have stopped menstruating as a result of arduous exercise training that has
interfered with the normal secretion of the reproductive hormones.10 Disturbing reports show that female athletes who
do not menstruate regularly have far less dense spinal bones-in other words, less calcium present-than both nonathletes
and female athletes who menstruate regularly.
Researchers have just begun to understand the importance of regular menstruation for the promotion of bone
maintenance. Current studies imply that a woman runner who does not menstruate regularly may also have a 4.5 times
higher risk for the development of a stress fracture. Female athletes whose menstrual cycles become irregular should
consult a physician to ascertain the cause. Decreasing the level of training and/or increasing body weight often restores
regular menstrual cycles. If irregular menstrual cycles persist, severe bone loss and osteoporosis may result. Extra calcium
in the diet does not necessarily compensate for this loss of menstruation, but inadequate dietary calcium can make matters
worse.
Ergogenic Aids:
Substances that Enhance Athletic Performance
Manipulating one's diet
As late as 30 years ago, American football players were encouraged on hot practice days to “toughen up” for competition by
liberally consuming salt tablets before and during practice and by not drinking water; now it is widely recognized that this practice
can be fatal. Today's athletes are as likely as their predecessors to experiment—bee pollen, seaweed, freeze-dried liver-flakes,
gelatin, ginseng, coenzyme Q10, creatine, amino acid supplements, and artichoke hearts are just some of the worthless substances
known today as “ergogenic” (work-producing) aids.17
Still, modern-day athletes can benefit from recently documented scientific evidence that some dietary substances do have
ergogenic properties. These include sufficient water, lots of carbohydrate, and a balanced and varied diet that follows suggestions
in The Daily Food Guide.4,11 Again, amino acid supplements are not in the list. The average American eats plenty of protein, athletes
included. Clearly, it is not possible to change average athletes into champions simply by altering diets. This means nutrient
supplements require careful evaluation. Use should be designed to meet a specific dietary weakness, such as a poor iron intake.
These and other aids whose benefit is often dubious and which nonetheless pose health risks must be given close scrutiny before
use. The risk-benefit ratio of these ergogenic aids especially needs to be examined; athletes must stay on guard against false
promises.
62
Bicarbonate loading
We have noted that muscles that contract vigorously during athletic performance produce lactate. Lactate build-up inhibits the
activity of enzymes involved in energy metabolism and leads to early fatigue. In the 1930s, athletes' attempts to counter this lactic
acid accumulation by ingesting small doses of sodium bicarbonate (a base) failed to improve their athletic performances. On the
other hand, more recent experiments using large doses of bicarbonate (30 milligrams per kilogram body weight) were consumed
l or 2 hours before exercise generally have improved strenuous performance lasting 2 to 10 minutes. About 20 minutes of warm
up must precede the event. The bicarbonate-loading apparently speeds the removal of lactate from contracting muscle cells.
Unfortunate side effects of large doses of sodium bicarbonate are nausea and diarrhea, often at unpredictable times. For this reason,
bicarbonate loading has so far not become popular with athletes.
Caffeine and performance
Drinking 3 to 4 cups of coffee (4 to 5 milligrams of caffeine per kilogram body weight) or using caffeine suppositories about 1 hour
before an endurance competition (lasting more than 2 hours) enhances performance in some, but not all, athletes. The effect is less
apparent in athletes who have ample stores of glycogen. The reason for the overall effect is not well established: increased use of
fatty acids for muscle fuel, psychological effects, or enhancement of glycolysis in muscle all deserve consideration. However, some
athletes experience changes in heart rhythm, nausea, or lightheadedness that can actually impair performance. Olympic officials
view caffeine as a drug and do not condone its use. They consider a body level of caffeine exceeding the equivalent of 5 to 6 cups
of coffee illegal.
Anabolic steroids
Public attention focused on the use of anabolic steroids when Ben Johnson, winner of the gold medal for the 100-meter dash in the
1988 Olympic Games, was disqualified. Johnson acknowledged that he took anabolic-androgenic steroids regularly as part of his
training regimen. These steroids are used by athletes to enhance performance in a variety of sports, most commonly .strength sports.
such as football, wrestling, weight lifting, and certain track-and-field events. Steroids have also been used by swimmers and cyclists
and are often used by male and female body builders and even nonathletic high school students in an attempt to “get big.”
Steroids are synthetic versions of sex hormones that promote two types of effects: masculinization (androgenic) and growth
promotion (anabolic). Athletes have taken these drugs, often in doses 10 to 30 times normal androgen output, to increase muscle
size, strength, and performance; yet no systematic cardiovascular benefit has been found. .
Although they can increase muscle mass, especially in people with low androgen output, steroid use is unsafe and, in athletics,
illegal. The consequences of steroid use also can occasionally be devastating: they cause growth plates in bones to close
prematurely (thus limiting the adult height of a teenage athlete), produce bloody cysts in the liver, accelerate the development of
heart disease, high blood pressure, sterility, and many other detrimental physical effects. Psychological consequences vary from
increasing aggressiveness, drug dependence, and mood swings to decreased sex drive, depression, and even “roid-rage” (violence
attributed to steroid use).9 Some football players consider the increased aggressiveness an additional benefit.
Athletes may begin to use steroids during high school, and perhaps as early as junior high school. Many serious athletes must
make a hard choice--to not use steroids and face a large field of artificially endowed opponents, or to use the drugs and risk side
effects.
Growth hormone
There is too little scientific information available on the effects of growth hormone on muscle mass and strength to allow
firm conclusions to be made about this drug. However, it is known that the skin, tongue, and bones may grow abnormally
under growth hormone stimulation. Abusing growth hormone may increase height if consumed at critical ages, but
uncontrolled growth of the heart and other internal organs and even death are also potential consequences. All in all, use
of growth hormone is dangerous—it requires careful physician monitoring. Arginine and ornithine supplements, basically
amino acids, a new rage among body builders, are promoted as growth hormone boosters. Current evidence suggests that
any increase in growth hormone after consuming amino acids is rather modest and probably of little physiological
consequence.
Blood doping
Injecting red blood cells into the bloodstream-known as blood doping-is used to try to enhance aerobic capacity. In this
procedure, an athlete donates at least 2 pints of blood at least 6 weeks prior to the event and freezes the cells while the body
makes more blood to replace it. Then, a day or two before competition, the frozen red cells are thawed and reinfused into
the veins; the added cells elevate the total red blood cell count and hemoglobin concentration above normal.
Studies of blood doping show that it is a viable means to improve endurance performance. Admissions by world-class
athletes—including members of the victorious U.S. cycling team in the 1984 Olympics—that they used blood doping to
reduce race times continue to stimulate questions about both sports ethics and how well the procedure actually works.
63
Several studies confirm an aerobic benefit to the athlete as a result of blood doping, but the possible negative health
consequences remain to be determined. It is also an illegal practice under Olympic guidelines.
Phosphate loading
Contrary to beliefs of many athletes and coaches, phosphate pills do not always improve performance or efficiency of heart
function during endurance events. Some studies have suggested that loading phosphate for 4 days increased the levels of
a metabolically important phosphate compound,
diphosphoglycerate (DPG), in red blood cells. These
studies also showed that increased levels of DPG
potentially improved the delivery of oxygen to
muscles and reduced work by the heart during
vigorous exercise. We now know that rigorously
trained athletes already have high levels of DPG in
4000 kcalories:
their red blood cells. Thus, although a single dose of
623 grams of carbohydrates
(61% of kcalories)
phosphate can induce blood chemistry changes, it does
139 grams of protein
(14% of kcalories)
not reliably improve the ability to perform endurance
118 grams of fat
(26% of kcalories)
exercise nor does it necessarily increase the efficiency
of aerobic metabolism.
Menu
Carbohydrate (grams)
Table 4: A 600-gram
Carbohydrate Diet
Pre-event Meal
A light meal (300 kcalories) should be eaten 2 to 4
hours before an endurance event to top off muscle
and liver glycogen stores. The meal should consist
primarily of carbohydrate, contain little fat or fiber,
and include a moderate amount of protein.5 Good
choices are spaghetti, bagels, muffins, bread, and
breakfast cereals with lowfat milk. Liquid meal
replacement formulas also can be used. Eat especially
fiber-rich foods the previous day to help clear the
bowels before the event, but not the night before.
Foods to avoid are those that are fatty or fried, such
as sausage, bacon, sauces, and gravies. A meal high
in carbohydrate is quickly digested, promotes normal
blood sugar levels, and avoids the need to dip right
away into glycogen stores. If an athlete feels a preevent meal harms performance, eating a highcarbohydrate diet the day and night before can help
meet the same goal.
Eating candy bars or drinking carbohydrate
beverages 15 to 45 minutes before competition was
previously thought to adversely affect performance
because it increases insulin release, and insulin
causes blood sugar to fall. However, such feedings do
not cause premature fatigue nor decrease endurance
for most people. In fact, recent studies show positive
benefits of this type of pre-event feeding.15 However,
there are undoubtedly a few athletes who are
extremely sensitive to an insulin surge. Thus, athletes
should experiment with pre-event carbohydrate
feedings to see if their performance is adversely or
positively affected.
Breakfast
1 orange
2 cups oatmeal
1 cup skim milk
2 bran muffins
14
50
12
48
Snacks
3/4 cup chopped dates
98
Lunch
Lettuce salad:
1 cup romaine lettuce
1 cup garbanzo beans
1/2 cup alfalfa sprouts
2 Tablespoon French dressing
3 cups macaroni and cheese
1 cup apple juice
2
45
5.5
2
80
28
Snack
2 slices whole-wheat toast
1 teaspoon margarine
2 Tablespoon jam
26
—
14
Dinner
2 ounce turkey breast (no skin)
2 cups mashed potatoes
1 cup peas and onions
1 banana
1 cup skim milk
74
23
27
12
Snack
1 cup pasta with
2 teaspoon margarine and
2 Tablespoon parmesan cheese
1 cup cranberry juice
33
—
—
36
TOTAL
628 grams
A carbohydrate:protein:fat ratio, of 60:15:25 is a good goal when
planning a diet to aid athletic performance.
64
Optimizing Body Fluids and Energy Stores During Exercise
Athletes need enough water to maintain the body's ability to regulate its internal temperature and so keep itself cool.2 Most
energy released during metabolism appears immediately as heat, and unless this heat is quickly dissipated, heat cramps,
heat exhaustion, or deadly heat stroke may ensue. Sweat evaporating from the skin helps remove this heat from the body,
and sweat rates during prolonged exercise range from 3 to 8 cups (750 to 2000 milliliters) per hour. To keep the body from
becoming dehydrated, fluid intake during exercise, when possible, should be adequate to minimize body weight loss.
However , most athletes find it very uncomfortable to replace more than about 75% to 80% of this sweat loss during
exercise.
By experimenting, athletes can determine how much fluid they require to maintain weight and how much fluid intake
they can tolerate without experiencing stomach cramps. This determination will be most accurate if the athlete is weighed
before and after a typical workout. For every 1 pound (½ kilogram) lost, 2 cups (0.5 liter) of water should be consumed
during exercise or immediately afterward. For example, an athlete who loses 5 pounds during practice should drink 10
cups of water, that is, perhaps 7 to 8 cups during practice and 2 to 3 cups following practice.
Thirst is not a reliable indicator of fluid need. By relying on thirst alone, an athlete might take 48 hours to replenish
fluid loss. After several days of practice, the increasing fluid debt can begin to impair performance. By the time one feels
thirsty, the person may have lost three percent of body weight through sweat.
A good rule of thumb is to drink beverages freely up to 2 hours before an event. Don't worry about thirst. Then
consume 1 to 2 cups (0.25 to 0.5 liters) of fluid about 15 minutes before a sports event. This is called hyperhydration.
The extra fluid in the body will be ready to replace sweat losses as needed. Next, consume approximately 1–1.5 cups of
fluid each 15 minutes for events that last longer than 30 minutes.5 If the weather is hot and/or humid, even more fluids
may be required. The athlete need not worry that gradual consumption of fluids will cause bloating or impair performance.
But skipping fluids will almost certainly cause problems! Alcohol and caffeine both have a dehydrating effect on the body,
so they should not be part of any hydration plan during exercise.
Sports Drinks: Do They Work?
A question that often arises is whether to drink water or a sportstype carbohydrate-electrolyte drink during competition. For
sports that require less than 30 minutes of exertion, replacing the
water lost in sweat is the primary concern because losses of
body carbohydrate stores and electrolytes (sodium, chloride,
potassium, and other minerals) are not usually too severe in such
activities. Electroly1es are lost in sweat, but the quantities lost
in exercise of brief to moderate duration can be easily replaced
later by consuming normal foods, such as orange juice, potatoes,
or tomato juice.
Water is certainly cheaper than a sports drink. But sportstype drinks can taste better than water, which may make one
drink more often-a clear benefit for fluid replenishment. In
addition, the carbohydrate in these drinks quickly replace
carbohydrate used up during practice or competition. The
sodium present also aids glucose absorption.
For endurance athletes, i.e., those whose sports demand
exertion for longer than 30 minutes, the discussion of sports
drinks becomes more critical. Beverages for the endurance
athlete must provide water for hydration, electrolytes to enhance
water absorption from the intestine and to help retain blood
plasma volume, and carbohydrate to provide energy.
Prolonged exercise results in large sweat losses, and some
of the fluid for sweating comes from blood plasma. If plain
water is used to replace the fluid losses in the blood, the
concentration of essential electrolytes may become too diluted.
This makes it important to include small amounts of sodium and
potassium in a sports drink to help maintain blood volume.
Including carbohydrates in sports drinks also have been
found to delay fatigue in endurance exercise.15 In exercise at
intensities of 65% to 75% of VO2 max (3 hour marathon pace),
ingesting carbohydrate improves performance, presumably by
either preventing great drops in blood glucose levels or by
providing an outside source of glucose for muscle use.
The amount of carbohydrate recommended for consumption
about 15 minutes before endurance exercise is 1 to 2 cups of a
10% to 20% solution of carbohydrate (10 to 20 grams of
carbohydrate per 100 milliliters of water). Once exercise begins,
1/2 to 1 cup of a 5% to 8% carbohydrate solution (5 to 8 grams
per 100 milliliters of fluid) should be consumed every 15 to 20
minutes.15 This is the carbohydrate concentration of typical
sports drinks. A variety of brands of beverages can be used for
fluid, electrolyte, and carbohydrate replacement. Some beverage
labels mention glucose polymers (molecules of glucose linked
together in short chains). Solutions containing glucose polymers
were initially thought to empty from the stomach faster than
solutions containing glucose. We now know that there's little
difference in stomach emptying times between sports drinks
containing glucose polymers and those containing simple sugars
such as glucose or sucrose: Furthermore, comparisons of drinks
containing glucose polymers (more properly known as
maltodextrins), glucose, or sucrose show that all of these
carbohydrates have similar positive effects on exercise
performance and physiological function as long as the
concentrations of carbohydrate are in the 5% to 8% range. The
exception to this rule is drinks whose only carbohydrate source
is fructose. Fructose is absorbed from the intestine more slowly
than glucose and often causes bloating or diarrhea.
65
Carbohydrate Intake During Recovery From Exercise
A large portion of carbohydrate food—about 4 grams of carbohydrate per pound (about 9 grams of carbohydrate per
kilogram) of body weight—should be consumed within 2 hours of a training exercise bout, and the sooner the better.15
This period of time is when glycogen synthesis is the greatest. Athletes who are training hard can consume a simple sugar
candy, sugared soft drink, fruit juice, or a carbohydrate supplement right after training as they attempt to reload their
muscles with glycogen. At fast-food restaurants the athlete can order extra crust on pizza, load up at the salad bar, and
have extra rolls and muffins.
Fluid and electrolyte intake is also an essential component of the athlete's recovery diet. This helps reestablish normal
levels of body fluids as quickly as possible. This is especially true if two workouts a day are followed and if the
environment is hot and humid.
It cannot be emphasized enough that any nutrition strategies, including fluid replacement, should be tested out during
practice and. trial runs. An athlete should never try a new food or beverage on the day of competition. Some food items
or beverages may not be tolerated well, and the day of competition is not the time to find that out.
Muscle Bulking Diets
During muscle-building regimens, athletes should consume 1 to 1.5 grams of protein per kilogram (0.5 to 0.7 grams per
pound) of body weight every day.14 Anyone eating a variety of foods can easily do that. For example, a 123 pound (5;3
kilogram) woman can consume close to her upper range of 80 grams of protein by consuming 4 ounces of chicken (one
chicken breast), 3 ounces of beef (a small lean hamburger) and 3 glasses of milk during a single day. And this does not
even include the protein in the grains or vegetables she will also eat. A 180 pound (77 kilogram) man needs only to
consume 6 ounces of chicken (a large chicken breast), a 6-ounce can of tuna, and 3 glasses of milk during a day to obtain
close to his upper range of 115 grams of protein. Many athletes eat much larger portions in order to meet their energy
needs. Thus, protein supplements are not needed for athletes because their diets typically exceed even these generous
protein recommendations.
Athletes who either feel they must significantly limit their energy intake or are vegetarians should determine how
much protein they eat; they should make sure it equals at least 1 gram per kilogram of desirable body weight. Skimping
on protein is not a good idea.5
Overall, following a high carbohydrate diet that follows the Daily Food Guide is a goal all athletes should consider.
Weekend athletes would be well advised to do the same, as the many health benefits accrued add to those from the
exercise.3,8
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
14.
15.
16.
17.
18.
Aronsen V A: Vitamins and minerals as ergogenic aids, The Physician and Sports Medicine 14:209, 1988.
Barr S and Costill D: Water: Can the endurance athlete get too much of a good thing? Journal of the American Dietetics Association
89: 1629,1989.
Blair SW and others: Physical fitness and all-cause mortality, Journal of the American Medical Association 262:2395, 1989.
Burke L and Read R: Sports Nutrition: approaching the nineties, Sports Medicine 8:80, 1989.
Clark N: Nancy Clark's sports nutrition guidebook: eating to fuel your active lifestyle, Champaign, Ill, 1990, Leisure Press.
Costill D: Inside running: basics of sports physiology, Indianapolis, IN, 1985, Benchmark Press.
Costill D: Carbohydrates for exercise: Dietary demands for optimal performance, International Journal of Sports Medicine 9:1, 1988.
Hagen R D: Benefits of aerobic conditioning and diet for overweight adults, Sports Medicine 5:144, 1988.
Hallagan JB and others: Anabolic-androgenic steroid use by athletes, The New England Journal of Medicine 321:1042, 1989.
Highet R: Athletic amenorrhea: An update on etiology, complications and management, Sports Medicine 7:82, 1989.
Hultman E: Nutritional effects on work performance, American Journal of Clinical Nutrition 49:949,1989.
Lamb D: Physiology of exercise: responses and adaptations, New York, 1984, MacMillan Press. 13. Murray RD and others: Harper's
Biochemistry, Norwalk, Conn, 1988, Appleton and Lange.
Paul G: Dietary protein requirements of physically active individuals, Sports Medicine 8:154, 1989.
Sherman M and Lamb D: Nutrition and prolonged exercise. In Lamb, D and Murray, R (eds): Perspectives in exercise science and
sports medicine: prolonged exercise, Indianapolis, IN, 1988, Benchmark Press.
Stryer L: Biochemistry, ed 3, New York, 1988, W H Freeman.
Williams M: Beyond training: How athletes enhance performance legally and illegally, Champaign, 111,1989, Leisure Press."
Williams MH: Nutritional ergogenic aids and athletic performance, Nutrition Today, January/February: 7, 1989.
66
The Newsletter of Athletic Performance
OPTIMAL PERFORMANCE
ANAEROBIC THRESHOLD TRAINING
When it comes to training for endurance sports, serious
athletes and coaches identify specific training intensities
and frequently associate them with anaerobic threshold
(AT). Many exercise scientists agree that training at or near
the AT on a regular basis makes a major contribution to an
athlete's ability to perform at top aerobic capacity and
improve performance.
AT is a borderline marker between aerobic (with
oxygen) and anaerobic (without oxygen) exercise. In
theory, AT is the highest level of exercise your body can
maintain over an extended period of time. Cross this border
and increase your level of exertion for your workout, and
your body will begin to produce more lactic acid—the
breakdown product of anaerobically metabolized
glucose—than it can eliminate. When the muscles function
anaerobically, they cannot clear the accumulating lactic
acid and the associated hydrogen ions. This combination
of factors eventually leads to exhaustion.
Exercise scientists know that in order to increase your
ability to maintain high aerobic intensity for a long period of
time, you need to train at just about your current AT. By
exercising at this intensity, you “teach” your body to tolerate
the discomfort associated with higher levels of lactic acid,
becoming better equipped over time to clear it away. By
including several high-intensity workouts per week at the
proper level—determined by the athlete's individual ATrelated heart rate, time, or speed for a certain
distance—endurance and overall performance will improve.
Francesco Conconi, M.D., Ph.D., professor of applied
biochemistry at the University of Ferrara in Italy and an
innovator in AT-training, believes that “the ability of athletes
to perform at or near their AT in training is a very good
indicator of how they will perform in competitive endurance
events.”
In order to achieve your athletic potential, you need to
challenge yourself with weekly AT workouts. The following
sport-specific AT strategies are designed to get you started
training more effectively.
RUNNING
“Middle- to long-distance runners will benefit greatly from
AT training,” says exercise physiologist Jack Daniels,
Ph.D., the cross-country and distance running coach at the
State University of New York at Cortland.
Finding your AT One easy gauge of your current AT
is found by monitoring your breathing pattern. If you can
comfortably maintain a 2/2 pace as you run—taking two
Vol. 3 No. 1 September 1994
steps while you breathe in and two steps as you breathe
out—and hold this pace for at least 20 minutes, you are
probably close to your AT. “If you have to breathe any
faster than this rhythm or if It becomes uncomfortable to
keep up this pace,” says Daniels, “you are probably over
your AT and need to pull back a little.”
Your 5K race pace is another way to find your AT.
“Add about 6 seconds per 400 meters, or 24 seconds per
1,500 meters to your current 5K time and you have your AT
level," says Daniels, who has conducted blood lactate
studies of runners to verify this running pace.
You can also find your AT by using a heart rate monitor
or taking your pulse. But first, you need to know your
maximum training heart rate. To do so, perform a set of
three four-minute intervals, with three-minute rests
between. Note your heart rate after each run, and average
them out to find your maximum training heart rate. “Eightyfive to ninety percent of your maximum training heart rate
is a good indicator of your current AT," says Daniels.
Workouts Daniels breaks his AT running workouts into
two distinct types: tempo runs and cruise intervals. To
perform a tempo run, get in a good warm up (so you are
sweating) and then run tor 20 minutes while maintaining
your AT pace. "Lactic acid should be accumulatlng slowly,"
notes Daniels, “and about five minutes into your run, it
should reach a level that won't be exceeded for the
remainder of your run."
Cruise intervals consist of running at threshold pace,
just as with tempo runs, but these intervals are broken up
with short rest periods of one minute or less. Here's an
example of a mid-week AT-workout:
6-8 x 1,000 meters at AT pace with a 1-minute rest
recovery after each interval, or 4-5 x 1 mile at AT pace with
a 1-minute rest recovery after each interval.
SWIMMING
Ernie Maglischo, Ph,D., an exercise physiologist and men's
swimming coach at Arizona State University, has used AT
training with his athletes for the past decade. "Training by
AT is standard procedure in Europe," says Maglischo, "but
it's hard for many American swimmers to understand the
concept of AT training because they are of a mind-set to
push as hard as they can in every workout, trying to top
their best lap time. Or else they go too slow in a workout
due to built-up fatigue from previous workouts. They don't
want to train at this middle ground, which is the AT level."
However, Maglischo notes that once his athletes come
around to his way of thinking and start following his ATbased training schedules, their times begin to drop.
Finding your AT Maglischo recommends warming up,
then swimming 3,000 meters non-stop. "Take your 100-
67
meter pace time from this swim," says Maglischo. “A few
seconds slower than this is your AT pace. Also, by
correlating your 100-meter splits with heart rate monitoring,
you can use heart rates as a good indicator of your AT
level."
Workouts Maglischo uses the following three levels
endurance training with his swimmers:
• Threshold: Workouts at your current AT level.
• Endurance: Workouts 3 to 5 seconds slower per
100 meters than your AT pace.
• Overload: Workouts 1 to 2 seconds faster per 100
meters than your AT pace.
If you are training at least five days a week for 45 to 90
minutes, Maglischo recommends including the following in
your workouts:
• One overload session per week totaling 20 minutes
non-stop.
• At least two 30- to 40-minute specific threshold
sessions per week, at either Threshold or Endurance pace.
If you're performing two daily workouts, don't do more than
two AT workouts in a row.
• Minimal AT training on recovery days or on those
days without any planned AT training. This can consist of
at least 600 meters at AT pace.
BICYCLING
By varying your workout paces throughout the week at
different speeds and heart-rate levels, you can make
measurable improvement in your speed and endurance
capabilities. “Serious cyclists need workable training
formats," says John Howard, three-time Olympic cyclist
and current national master's mountain bike champion.
“Using your heart rate and bike speed, you can find your
level and simplify the process of effective training."
Finding your AT After a good warm-up, ride for one
hour nonstop and monitor your heart rate. .AT will be that
heart rate or speed you can maintain steadily for that hourlong ride," says Howard.
Workouts “I break workouts into several training
paces, each defined as a percentage of AT," says Howard.
These paces include:
• AT Stimulation: Perform these workouts at 90% of
your AT or higher. .AT stimulation rides represent the bulk
of your primary speed work," says Howard. Find a course
without traffic lights or stop signs. Use your main racing
gear and reduce cadence to a comfortable race leveI (75
to 90 rpm). Perform 10 intervals of 3 to 5 minutes, with
equal recovery intervals.
• Endurance cycling: Ride at 75% to 85% of your
AT. Training at this level accustoms the cyclist to long
hours in the saddle. Spend 3 to 6 hours spinning 85 to 90
rpm in small- to medium-sized gears. Perform this workout
once or twice a week, with your succeeding workout being
a recovery day ride.
• Recovery day ride: Per1ormed at 65% to 70% of
AT. This range is where you will spend your time between
hard efforts without losing fitness. This is your maintenance
pace, with workouts consisting of 1 to 2 hours of easy lowgear spinning (90 to 100 rpm).
In addition, Howard recommends a speed workout
during the week consisting of high-output intervals and
short rests (12 x 2-minute sprints) performed at 15% higher
than your AT. Also, during the course of one of your other
rides, add maximum sprint training by performing 3 to 5 allout sprints of 20 to 30 seconds.
WEIGHT TRAINING
To enhance your ability to tolerate lactic acid in other
sports, use weight-training workouts specifically designed
to stimulate lactic acid production. Athletes who want to
make more gains and improve the high-intensity endurance
of a muscle or muscle group need to shorten the rest
period between sets to a range of 30 seconds to 1 minute.
“By exercising this way," says William J. Kraemer, Ph.D.,
director of research at Penn State's Center for Sports
Medicine and a member of the Newsletter's Board of
Advisors, “you train those muscles to tolerate the disruption
of the acid-base balance and perform better with higher
levels of lactic acid." It is estimated that it will require
approximately 10 weeks (1 to 2 workouts per week) before
improvement will be seen with lactic acid tolerance while
weight training. This may well have a positive effect on your
AT in sports.
Workout The following general workout should be
performed at least twice weekly to realize appreciable
gains. Use a 10 RM (Repetition Maximum, a weight you
can lift 10 times, but not more), and perform 3 sets of 10
repetitions.
If just starting out, take a 2-minute rest between sets.
As you get stronger (and if you don't feel dizzy or
nauseated), gradually reduce the rest periods to 90
seconds, 75 seconds, and finally 1 minute.
This technique should be used with the following
resistance exercises:
Squat, bench press. seated row, double knee
extension, military press, calf raise, lat pull-down, sit-ups
(perform 25 with a weight behind your head), and leg
press.

Energy - Exercise Sciences!

Transcription

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