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Nutrition, Body
Composition
and Performance
CHAPTER OBJECTIVES
• Describe the effect of various carbohydrate diets on
muscle glycogen and on endurance performance
during heavy exercise.
• Discuss the method of achieving a
supercompensation of the muscle glycogen stores.
• Describe the importance of blood glucose as a fuel
in prolonged exercise, and the role of carbohydrate
supplementation during performance.
• Describe the role of fats and proteins as fuel during
performance.
• Explain the role of vitamins and minerals to the
athlete and their importance to performance.
Nutrition and Sport
• Recommended macronutrient balance
– Carbohydrate: 45 to 65% of daily kilocalories
• Meets needs of whole population
• Addresses special needs (type 2 diabetes)
• Athletes need more carbohydrates that the average person
– Fat: 20-35% (<10% saturated)
– Protein: 10 to 35%
• Optimal for both performance and health
Nutrition and Sport:
Classification of Nutrients
• Carbohydrate (CHO)
• Fat (lipid)
• Protein
• Vitamins
• Minerals
• Water
Nutrition and Sport:
Classification of Nutrients—CHO
• Molecular composition
– Monosaccharide, disaccharide, or polysaccharide
– Monosaccharides: glucose, fructose, galactose
• Functions in body
– Energy source (sole source for nervous system)
– Regulate fat and protein metabolism
• Consumption and storage
– Excess CHO stored as glycogen
– Dietary CHO intake determines glycogen stores
Nutrition and Sport:
Classification of Nutrients—CHO
• Determinants of glycogen replacement
– CHO intake
– Exercise type (eccentric   glycogen synthesis)
• Glycogen maintenance
– Requires 5 to 13 g CHO/kg body weight per day
– In athletes, hunger often insufficient drive for CHO
consumption
– Insufficient CHO intake  heavy, tired feeling
Figure 15.8
Figure 15.9
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
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
Classic vs Modified Method of
Supercompensation
Glycemic Index
• Glycemic index (GI) categorizes food based
on glycemic (blood sugar) response
– High GI (GI >70): sport drinks, jelly beans,
baked/fried potatoes, cornflakes, pretzels
– Moderate GI (GI 56-70): pastry, pita bread, white
rice, bananas, soda, ice cream
– Low GI (GI ≤55): spaghetti, legumes, milk,
apples/pears, peanuts, M&M’s, yogurt
CHO Intake Prior to 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 1-4 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
https://www.youtube.com/watch?v=9-e5y-3dyUs
https://www.youtube.com/watch?v=x3NimHt_shE
Figure 15.11
CHO Intake During Exercise
• CHO during exercise
– Unlike preexercise CHO, does not trigger
hypoglycemia (can maintain plasma glucose even
as glycogen is depleted)
– Improved muscle permeability to glucose?
– Insulin-binding sites altered during exercise?
• 30-60g CHO/hr is required
– 375-750 ml/hr of 8% CHO solution (>8% slows
gastric emptying)(Isotonic vs Hypotonic)
– Addition of caffeine increase CHO oxidation
– Adding protein could increase performance further
Blood Glucose Use During Prolonged
Exercise
Protein 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:
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Training state of the subject
Quality and quantity of protein consumed
Total calories consumed (positive caloric balance)
The body’s carbohydrate stores
Intensity, duration, and type of exercise
• Used to determine protein requirements for athletes
Protein and Sport Performance
• Protein essential for body function
– Cell structure, growth, repair, and maintenance
– Used to produce enzymes, hormones, antibodies,
and as buffer
– Controls plasma volume via oncotic pressure
Recommended Protein Intake
• RDA (adults)
– 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
Water and Electrolyte Balance
• Dehydration during exercise
– Sweat  due to higher body temperature
– Water loss > water gain
– 2% total body weight
• Body temperature and sweating affected by
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Environmental temperature, radiant heat load
Humidity
Air velocity
Body size
Metabolic rate
Physiological Effects of Dehydration
• Decreases in:
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SV, HR, Q
Peak blood lactate
Buffering capacity of the blood
Lactate threshold
Muscle and liver glycogen
Sweat rate
Skin blood flow
• Increase in:
– Core temperature
Dehydration
and Exercise Performance
• Thirst
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Osmoreceptors (high blood osmolality)
Baroreceptors (low blood volume)
Thirst not well calibrated to hydration levels
24 to 48 h to completely rehydrate
• Benefits of fluids before and during ex
– Minimize dehydration and water loss
– Performance and cardiovascular function maintained
Hydration
• Before Exercise
– For exercise less than one hour
• 300-500 ml water (10-16oz)
• Containing 30-50 g CHO
– For exercise durations more than one hour
• 300–500 ml water only
• During Exercise
– Fluid replacement during exercise associated with:
• Lower HR, core temp and RPE
– Recommendations:
• Events <1 hour: 500–1,000 ml water only (16-33oz)
• Events of 1–3 hrs: 500–1,600 ml water + Na+, Cl-, and glu
• Events >3 hours: 500–1,000 ml water + Na+, Cl-, and glu
Effect of Fluid Replacement
• Fluid replacement
during exercise
associated with:
– Lower exercise HR
– Lower core temp
– Lower RPE
(objective AND
subjective benefits)
Factors Affecting Absorption of Fluid
Classification of Nutrients—Vitamins
• Small but essential organic molecules
– Enable use of other ingested nutrients
– Act as catalysts and cofactors in chemical reactions
• Coenzymes associated with aerobic metabolism
• Fat soluble versus water soluble
– Fat soluble stored, can reach toxic accumulations
– Water soluble excrete, toxicity difficult to reach
• In general, unless vitamin deficiency exists,
supplementation NOT helpful
Classification of Nutrients—Vitamins
• B-complex vitamins (12+ total)
– Essential for cellular metabolism, ATP production
– Needed for pyruvate  acetyl-CoA, formation of
FAD and NADP, erythropoiesis
• Vitamin C
– Important for collagen maintenance, antioxidant
– Also, adrenal hormone synthesis, iron absorption
• Vitamin E
– Stored in muscle and fat
– Potent antioxidant
Classification
of Nutrients—Antioxidants
• Free radicals
– Cellular by-product of oxidative phosphorylation
– Highly reactive, may precipitate fatigue
• Antioxidants
– Quench free radicals, prevent oxidant damage
– Muscle antioxidant enzymes
– Dietary antioxidants: vitamins E and C, b-carotene
Classification of Nutrients—Minerals
• Minerals
– Inorganic substances needed for cellular function
– Calcium
• Bone density, nerve and muscle function
• Concerns: osteopenia, osteoporosis
– Sodium, potassium, chloride
• Na+, Cl- found primarily in interstitial fluid
• K+ in intracellular fluid
• Needed for nerve impulses, cardiac rhythm, fluid and pH
balance
• Excess intake can be dangerous
Classification of Nutrients—Minerals
• Iron
– Critical for hemoglobin, myoglobin (O2 transport)
– Deficiency  anemia
– 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
– Iron supplementation
• Rapidly restores hematocrit and VO2max
• Slower increase in mitochondrial activity and endurance
• Increase iron intake through foods
– Supplements may be indicated
The Athlete’s Diet
• Vegetarian diets
– Vegan, lacto, lacto-ovo
– Lacto-ovo fewer nutrition deficiencies
– Need sufficient essential amino acids, total
kilocalories, vitamin A, riboflavin, vitamin B12, vitamin
D, Ca2+, zinc, iron
**ExPhysRules
Precompetiton Meal
• Purposes
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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
Body 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
Body Fat 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
Somatotypes Ath vs Adults