nutrition, body composition, and performance

Scott K. Powers • Edward T. HowleyScott K. Powers • Edward T. HowleyScott K. Powers • Edward T. HowleyScott K. Powers • Edward T. Howley

Theory and Application to Fitness and PerformanceTheory and Application to Fitness and PerformanceSEVENTH EDITION

Chapter

Presentation prepared by:

Brian B. Parr, Ph.D.

University of South Carolina Aiken

Copyright ©2009 The McGraw-Hill Companies, Inc. Permission required for reproduction or display outside of classroom use.

Nutrition, Body Composition, and Performance

Chapter 23

Copyright ©2009 The McGraw-Hill Companies, Inc. 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.

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Objectives

8. Describe the recommended fluid replacement strategies for athletic events of different intensities and durations, citing evidence to support your position.

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.

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Objectives

12. Characterize the role of the pregame meal on performance and the rationale for limiting fats and proteins.

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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Outline

Nutrition and Performance

Carbohydrate

Protein

Water and Electrolytes

Minerals

Vitamins

Precompetition Diet

Body Composition and Performance

SomatotypeBody Fatness and

Performance

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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 than the average person Average intake only ~50% calories

• 20–35% calories from fat• 10–35% calories from protein


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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


Figure 23.1

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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– Elevated muscle glycogen can last as long as five days


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Modification of the Classic Glycogen Loading Technique


Figure 23.2

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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


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The Winning Edge 23.1The Zone Diet

• 40% carbohydrate, 30% protein, 30% fat– Protein intake: 1.8–2.2 g/kg FFM– Leads to eicosanoid production

Promotes vasodilation and lipolysis

• Not recommended for endurance performance– Low-carbohydrate diet

Reduced time to exhaustion

– Protein guideline results in calorie-deficient diet– Oversimplification of metabolic and physiological

effects– Inconsistency in eicosanoid effects on muscle

• Should be considered “ergolytic” rather than “ergogenic”


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In Summary

Performance in endurance events is improved by a diet high in carbohydrates due primarily to the increase in muscle glycogen.

When workouts are tapered over several days while additional CHO (70% of dietary intake) is consumed, a “supercompensation” of the glycogen store can be achieved.


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Carbohydrates Prior to or During a Performance

• Improves performance by maintaining blood glucose– Rate of glucose use by muscle

1–2 g/min

– Rate of liver gluconeogenesis 0.2–0.4 g/min

• Does not spare muscle glycogen utilization • Allows maintenance of power output and lower

RPE


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Carbohydrates Prior to a Performance

• 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


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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 may increase performance further

Conflicting evidence


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Blood Glucose and Muscle Glycogen Use During Prolonged Exercise


Figure 23.3

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In Summary

Pre-exercise feedings should contain 1 to 5 g of carbohydrate per kilogram of body weight and should be taken one to four hours prior to exercise.

Muscle glycogen is depleted at the same rate, whether or not glucose is ingested during prolonged performance.

The ingestion of glucose solutions during exercise extends performance by providing carbohydrate to the muscle at a time when muscle glycogen is being depleted.


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Protein Requirement During Exercise

• Determined by:– Oxidation of individual amino acids (leucine)

Oxidation affected by carbohydrate intake Provides 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


Figure 23.4

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Effect of Initial Muscle Glycogen Levels on Sweat Urea Nitrogen Excretion


Figure 23.5

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Effect of Glucose Ingestion on the Rate of Leucine Metabolism


Figure 23.6

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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

10–18% calories from protein in vegetarians


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In Summary

The protein requirement for those engaged in light-to-moderate endurance exercise is equal to the RDA of 0.8 g•kg–1•d–1; however, it is 1.2–1.4 g•kg–1•d–1 for athletes who participate in high-intensity endurance exercise.

For resistance training, there is more dispute about the requirement. It may be only 0.9 g•kg–1•d–1 for those maintaining strength or as high as 1.6–1.7 g•kg–1•d–1 for those adding lean mass and strength.

Bottom line: The average protein intake of an athlete exceeds 1.5 g•kg–1•d–1, more than enough to cover the higher protein requirement.


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Fluid Replacement—Before Exercise

• Goal is to be euhydrated before exercise– Foods and beverages consumed before meals

should be sufficient• If additional fluids are needed:

– Slowly drink beverages at least four hours prior (~5–7 ml•kg–1)

– Drink more fluid if urine is dark or none is produced two hours prior (~3–5 ml•kg–1)

– Sodium in beverages of food helps retain fluid• No evidence that glycerol hyperhydration improves

performance• Increasing plasma volume with high sodium

beverages improves performance in the heat


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Water Replacement—During Exercise

• Goal is to reduce risk of excessive dehydration– Greater than 2% body weight loss

• Fluid replacement during exercise associated with:– Lower HR – Lower body temperature– Lower RPE

• Important for both prolonged and intermittent exercise


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Responses to Exercise With Different Volumes of Fluid Replacement


Figure 23.7

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• Athletes should estimate sweat rates– Measure pre- and post-exercise body weight

• Beverage characteristics– Temperature between 15–21°C– Contain ~20–30 mEq•L–1 sodium and 2–5 mEq•L–1 potassium– Contain 5–10% carbohydrate �

Mixture of glucose, sucrose, fructose, and maltodextrin results in greatest carbohydrate delivery

• Caffeine does not– Create water-electrolyte balance– Cause hyperthermia or reduce exercise-heat intolerance


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• 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% VO2 max


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Factors Affecting Fluid Absorption From the Gastrointestinal Tract


Figure 23.8

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• Recommendations:– Events <1 hour (80–130% VO2 max)

500–1,000 ml water only

– Events of 1–3 hours (60–90% VO2 max) Contain 10–20 mEq•L–1 NaCl and 6–8% carbohydrate 500–1,000 ml to meet carbohydrate need 800–1,600 ml water to meet fluid need

– Events >3 hours Contain 10–20 mEq•L–1 NaCl and 6–8% carbohydrate 500–1000 ml to meet carbohydrate and fluid need

– For rapid rehydration ~1.5 L fluid for every kg of weight loss


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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 replacement– Constant body weight indicates adequate salt and

water intake


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The Winning Edge 23.2Hyponatremia

• Dangerously low Na+ concentration– Plasma sodium ≤135 mM

• 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


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In Summary

Fluid replacement during exercise reduces the heart rate, body temperature, and perceived exertion responses to exercise, and the greater rate of fluid intake, the lower the responses.

Cold drinks are absorbed faster than warm drinks, and when exercise exceeds 65% to 70% VO2 max, gastric emptying decreases.

For exercise lasting less than one hour, the focus is on water replacement only. When exercise duration exceeds one hour, drinks should contain Na+, Cl–, and carbohydrate.


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In Summary

Salt needs are easily met at mealtime, and salt tablets are not needed. In fact, most Americans take in more salt than is required.


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Iron

• Deficiency affects VO2 max 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 VO2 max– 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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Recovery of Various Physiological Capacities with Iron Repletion


Figure 23.9

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Vitamins

• Important for energy production– Coenzymes associated with aerobic metabolism

• Supplementation: – Not necessary on well-balanced diet unless clear

deficiency is known Some small athletes who consume low-energy diets may

have deficiencies

– Toxicity with large doses of fat-soluble vitamins and vitamin C


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In Summary

Iron deficiency in American athletes may be related to an inadequate intake of dietary iron as well as a potentially greater loss in sweat and feces. In spite of this deficiency, athletes may absorb less than half of what a sedentary group of anemic individuals absorbs. Iron supplementation may be recommended for female athletes as a result of an annual clinical assessment of iron status.

Vitamin supplementation is unnecessary for an athlete on a well-balanced diet. However, for those with a clear deficiency, supplementation is warranted.


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Precompetition Diet

• Purposes– Provide adequate hydration– Provide carbohydrates to “top off” liver stores– Avoid the sensation of hunger– Minimize GI tract problems– Allow the stomach to be relatively empty at start of

competition


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Precompetition Diet

• Content– 500–1,000 kcals

3 hours prior to event

– Mostly complex carbohydrates Limit simple sugars, especially fructose

– 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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In Summary

The pregame meal should provide for hydration and adequate carbohydrate to “top off” stores while minimizing hunger symptoms, gas, and diarrhea. Varieties of commercially available liquid meals are consistent with these goals.


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• Body composition differs among athletes– Success in different events associated with certain

characteristics • Quantifying body composition

– Somatotype– Percent fat


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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

• Determining somatotype– 1 to 7 scale– Three-number sequence of three components

Somatotypes

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Extremes of Somatotypes

Somatotypes

Figure 23.10

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Contrast of Somatotypes Between College Students and Athletes

Somatotypes

Figure 23.11

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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– Be aware of error in measurement of percent fat

Somatotypes

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Percent Body Fat in Male and Female Athletes

Somatotypes

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In Summary

A somatotype is a numerical representation on a 1 to 7 scale of the degree to which a person possesses a high level of endomorphy, mesomorphy, or ectomorphy. Athletes are clearly different from the ordinary population, indicating a natural predisposition needed for success.

The body fat percentage consistent with excellence in performance is different for men and women, and varies within gender from sport to sport. Average values should not be applied to any single individual without regard to overall health status as seen in diet, sleep, and mental outlook. Further, it is “natural” for some athletes to have a higher body fatness than others in order to perform optimally.

Somatotypes

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Study Questions

1. What procedures would you follow to cause a supercompensation of muscle glycogen?

2. How much of a change in carbohydrate intake would be required for an individual who already achieves the dietary goal for carbohydrate?

3. How could glucose ingestion prior to exercise actually increase the rate of glycogen depletion?

4. Does carbohydrate ingestion during exercise slow down muscle glycogen depletion? Does it improve performance?

5. Is the protein requirement of an athlete higher than that of a sedentary person? Should protein intake be increased?

6. How would you recommend that a person replace water loss due to exercise?

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Study Questions

7. How does the fluid replacement strategy differ for short and long races?

8. How would you recommend that a potential iron deficiency anemia condition be dealt with?

9. Does an athlete need additional vitamins for optimal performance? Why?

10. What are the primary considerations for a pregame meal?

11. What is somatotype, and how is it different for athletes compared to the average college population?

12. Given a female distance runner with 17% body fat, what should you consider before recommendation for change?

nutrition, body composition, and performance

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