Chapter 23
Nutrition, Body Composition,
and Performance
EXERCISE PHYSIOLOGY
Theory and Application to Fitness and Performance, 6th edition
Scott K. Powers & Edward T. Howley
Presentation revised and updated by
Brian B. Parr, Ph.D.
University of South Carolina Aiken
© 2007 McGraw-Hill Higher Education. All Rights Reserved.
Objectives
1. Describe the effect of various carbohydrate diets on
muscle glycogen and on endurance performance
during heavy exercise.
2. Contrast the “classic” method of achieving a
supercompensation of the muscle glycogen stores
with the “modified” method.
3. Describe some potential problems when glucose is
ingested immediately prior to exercise.
4. Describe the importance of blood glucose as a fuel
in prolonged exercise, and the role of carbohydrate
supplementation during the performance.
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Objectives
5. Contrast the evidence that protein is oxidized at a
faster rate during exercise with the evidence that the
use of labeled amino acids may be an inappropriate
methodology to study this issue.
6. Describe the need for protein during the adaptation
to a new, more strenuous exercise level with the
protein need when the adaptation is complete.
7. Defend the recommendation that a protein intake
that is 12 to 15% of energy intake is sufficient to
meet an athlete’s need.
8. Describe the recommended fluid replacement
strategies for athletic events of different intensities
and durations, citing evidence to support your
position.
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Objectives
9. Describe the salt requirement of the athlete
compared to that of the sedentary individual, and the
recommended means of maintaining sodium
balance.
10. List the steps leading to iron deficiency anemia and
the special problem that athletes have in maintaining
iron balance.
11. Provide a brief summary of the effects of vitamin
supplementation on performance.
12. Characterize the role of the pregame meal on
performance and the rationale for limiting fats and
proteins.
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Objectives
13. Describe the various components of the somatotype
and what the following rating signify: 171, 711, and
117.
14. Describe what the endomorphic and mesomorphic
components in the Heath-Carter method of
somatotyping represent in conventional body
composition analysis.
15. Explain why one must be careful in recommending
specific body fatness values for individual athletes.
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Recommended Range of Nutrient Intakes
 45–65% calories from carbohydrates
– Meets needs of whole population
– Addresses special needs (type 2 diabetes)
– Athletes need more carbohydrates that the
average person
 20–35% calories from fat
 10–35% calories from protein
© 2007 McGraw-Hill Higher Education. All Rights Reserved.
Carbohydrate Diets and Performance
 Muscle glycogen is depleted during heavy exercise
– Time to exhaustion related to initial muscle
glycogen store
 Endurance performance is improved by a diet high in
carbohydrates
– Increases muscle glycogen and performance time
 Muscle glycogen loading (“supercompensation”)
– Goal is to maximize muscle glycogen in the days
leading up to an event
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Effect of Diet on Muscle Glycogen and
Time to Exhaustion
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Figure 23.1
Muscle Glycogen Supercompensation
 Classical method
– Prolonged strenuous exercise to deplete glycogen stores
– A high fat/protein diet for three days while continuing to train
– 90% CHO diet for three days with inactivity
 Modified plan
– Tapering workouts (90 to 40 minutes) over several days
while eating 50% CHO diet
– Two days of 20 minute workouts while eating 70% CHO diet
– Day of rest eating 70% CHO diet before event
 Both methods increase muscle glycogen to high levels
 Only one day with carbohydrate intake of 10 g/kg body weight
from high glycemic index foods required for very high muscle
glycogen levels
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Modification of
the Classic
Glycogen Loading
Technique
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Figure 23.2
Muscle Glycogen Replenishment
 Takes about 24 hours to replenish muscle glycogen
– Requires ingestion of 500–700 g carbohydrates
– Limiting factor is glucose transport across cell
membrane
 Timing of glucose ingestion after exercise
– Initiated immediately after exercise
– Repeated each 2 hours for 6 hours
 Type of carbohydrate
– Glucose or glucose polymers better than fructose
• Fructose may be better for replenishing liver glycogen
– Including protein may increase glucose uptake
© 2007 McGraw-Hill Higher Education. All Rights Reserved.
Carbohydrates Prior to a Performance
 Improves performance by maintaining blood glucose
– Does not spare muscle glycogen utilization
– Allows maintenance of power output and lower RPE
 Pre-exercise
– 1-5 grams CHO•kg-1 body weight
– 1-4 hours before exercise
– Easily digestible solid or liquid food
– Test for sensitivity to carbohydrate load in training
 Carbohydrate intake immediately prior to exercise may
impair performance
– Hypoglycemia in sensitive individuals
– Faster rate of muscle glycogen utilization
© 2007 McGraw-Hill Higher Education. All Rights Reserved.
Carbohydrates During a Performance
 Carbohydrate ingestion can maintain plasma glucose
even as glycogen is depleted
– Delays fatigue and improves performance
 Can be ingested throughout exercise or 30 minutes
prior to fatigue
 30-60 g CHO/hour is required
– 375–750 ml/hr of 8% CHO solution
• >8% CHO slows gastric emptying
• CHO from glucose, sucrose, or glucose polymers
– Addition of caffeine increases CHO oxidation
– Adding protein increases performance further
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Blood Glucose and Muscle Glycogen Use
During Prolonged Exercise
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Figure 23.3
Protein Requirement During Exercise
 Determined by:
– Oxidation of individual amino acids (Leucine)
• Oxidation affected by carbohydrate intake
• Provide no rationale for increasing protein intake
– Whole body nitrogen balance studies
• N excretion in urine and sweat
• Dependent upon:
- Training state of the subject
- Quality and quantity of protein consumed
- Total calories consumed
- The body’s carbohydrate stores
- Intensity, duration, and type of exercise
• Used to determine protein requirements for athletes
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Effect of Exercise on Nitrogen Balance
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Figure 23.4
Effect of Initial Muscle Glycogen Levels
on Sweat Urea Nitrogen Excretion
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Figure 23.5
Effect of Glucose Ingestion on the Rate of
Leucine Metabolism
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Figure 23.6
Dietary Goals for Athletes
 RDA
– 0.8 g•kg-1•day-1
• Met by diet having 12% calories from protein
 Endurance training
– 0.8 g•kg-1•day-1 for light to moderate exercise
– 1.2-1.4 g•kg-1•day-1 for high-intensity exercise
 Strength training
– 0.9 g•kg-1•day-1 for maintaining strength
– 1.6–1.7 g•kg-1•day-1 for adding muscle mass
 Average athlete intake
– 16% calories from protein or 1.5 g•kg-1•day-1
– Sufficient for most athletes
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Water Replacement—Before Exercise
 For exercise less than one hour
– 300-500 ml water
– Containing 30-50 g CHO
 For exercise durations more than one hour
– 300–500 ml water only
© 2007 McGraw-Hill Higher Education. All Rights Reserved.
Water Replacement—During Exercise
 Fluid replacement during exercise associated with:
– Lower HR
– Lower body temperature
– Lower RPE
 Recommendations:
– Events <1 hour
• 500–1,000 ml water only
– Events of 1–3 hours
• 500–1,600 ml water plus Na+, Cl-, and glucose
– Events >3 hours
• 500–1,000 ml water plus Na+, Cl-, and glucose
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Responses to
Exercise With
Different Volumes of
Fluid Replacement
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Figure 23.7
Water Replacement—During Exercise
 Factors affecting fluid absorption
– Glucose concentration
• Gastric emptying slower above 139 mM
– Fluid volume
• Optimal volume is 600 ml
– Temperature
• Cold drinks absorbed faster than warm drinks
– Exercise intensity
• Gastric emptying slower above 65-70% VO2max
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Factors Affecting Fluid Absorption From
the Gastrointestinal Tract
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Figure 23.8
Hyponatremia
 Dangerously low Na+ concentration
 Caused by rehydration with water or hyponatremic
drinks during long (4+ hours) events
– May lead to weight gain during event
 Recommendations:
– Work to minimize risk of both hyponatremia and
dehydration
– Drink to match fluid loss on a schedule
• Match fluid intake to sweat loss and thirst
– Consume salty foods and beverages
© 2007 McGraw-Hill Higher Education. All Rights Reserved.
Salt
 Athletes require more salt than sedentary individuals
– Must replace salt lost in sweat
– Most people consume more salt than is required
 Salt needs should be met at meals
– Not by consuming salt tablets
 Body weight is the best test of salt/water balance
– Constant body weight indicates adequate salt
intake
© 2007 McGraw-Hill Higher Education. All Rights Reserved.
Iron
 Deficiency affects VO2max and endurance
– Component of hemoglobin and cytochromes
 Iron deficiency in athletes
– Due to decreased intake and decreased
absorption
– Due to increased loss
• Through sweat, feces, and urine
 Iron supplementation
– Rapidly restores hematocrit and VO2max
– Slower increase in mitochondrial activity and
endurance
– Increase iron intake through foods
• Supplements may be indicated
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Stages of Iron Deficiency
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Table 23.1
Recovery of Various Physiological
Capacities with Iron Repletion
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Figure 23.9
Vitamins
 Important for energy production
– Coenzymes associated with aerobic metabolism
 Supplementation
– Not necessary on well-balanced diet unless clear
deficiency is known
– Toxicity with large doses of fat-soluble vitamins
and vitamin C
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Pre-Competition Diet
 Purposes
– Provide adequate hydration
– Provide carbohydrates to “top off” liver stores
– Avoid the sensation of hunger
– Minimize GI tract problems
 Content
– 500-1,000 kcals, 3 hours prior to event
– Mostly complex carbohydrates
– Low in fat
• Slowly digested
– Low in protein
• Contributes to acids in blood
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Example of Pregame Meals
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Table 23.2
Somatotypes
 Endomorphy
– Relative predominance of soft roundness and
large digestive viscera
 Mesomorphy
– Relative predominance of muscle, bone, and
connective tissue
 Ectomorphy
– Relative predominance of linearity and fragility
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Extremes of
Somatotypes
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Figure 23.10
Contrast of Somatotypes Between
College Students and Athletes
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Figure 23.11
Body Fatness and Performance
 Optimal body fatness for health
– Males: 10-25%
– Females: 15-25%
 Optimal body fatness for performance
– Differs between men and women
– Varies within gender and sport
– It is natural for some athletes to have higher body
fatness than others in order to perform optimally
– Should be based on individual health status, not
on team average
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Percent Body Fat in
Male and Female
Athletes
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Table 23.3