Transcript Body Composition in Sport

Body Composition
and Nutrition for Sport
CHAPTER 15 Overview
• Body composition in sport
– Assessment
– Sport performance
– Weight standards
– Achieving optimal weight
• Nutrition and sport
– Classification of nutrients
– Water and electrolyte balance
– Dehydration and exercise performance
– Athlete’s diet
– Sport drinks
Body Composition in Sport
• Body composition: body’s chemical and
molecular composition
• General models of body composition
– Chemical model
– Anatomical model
– Two-compartment model
Figure 15.1
Body Composition in Sport:
Assessment
• Provides more information
– Height and weight not enough to know fitness status
–  Percent body fat,  performance
• Body composition measured several ways
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Densitometry/hydrostatic weighing
DEXA
Air plethysmography
Skinfold
Bioelectric impedance
Body Composition in Sport:
Assessment
• Densitometry: measures body density
– Hydrostatic (underwater) weighing
– Muscle heavier than water, fat lighter than water
– Most commonly used method
• Limitations of hydrostatic weighing
– Lung air volume confounding
– Conversion of body density to percent fat
– Fat-free density varies among people
Figure 15.2
Body Composition in Sport:
Assessment
• DEXA
– Dual-energy X-ray absorptiometry
– Quantifies bone and soft-tissue composition
– Precise and reliable but expensive and technical
• Air plethysmography (Bod Pod)
– Another densitometry technique
– Air displacement (instead of water)
– Easy for subject, difficult for operator, expensive
Figure 15.3a
Figure 15.3b
Body Composition in Sport:
Assessment
• Skinfold
– Most widely used field technique
– Measures thickness at a minimum of three sites
– Uses quadratic equations, reasonably accurate
• Bioelectric impedance
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Electrodes on ankle, foot, wrist, hand
Current passes from proximal to distal sites
Fat-free mass good conductor, fat poor conductor
Reasonably accurate, could be better
Figure 15.5
Figure 15.6
Body Composition in Sport:
Sport Performance
• Fat-free mass (includes muscle)
– Important variable for athletes to know
–  Good for power, strength, muscle endurance
– But bad for aerobic endurance (more mass to carry)
• Relative body fat (percent body fat)
– Fat: dead weight but useful energy store
– Less fat usually = better performance
– Exceptions: sumo wrestler, swimmer, weight lifter
Body Composition in Sport:
Weight Standards
• Guide for optimal body size and
composition for a given sport
• Can be misleading
– Elite athletes define optimal performance
– But do elite athletes define optimal body?
– Not always the case
Figure 15.7
Body Composition in Sport:
Weight Standards
• Inappropriate use of weight standards
– Seriously abused by coaches, players
– Misconception that small weight loss good, large
weight loss better
– Can lead to  performance, eating disorders
• Making weight: severe weight loss
– Wrestling, boxing, etc.
– Weight classes can force extreme weight loss
– Compete in class too low  injury, poor health
Body Composition in Sport:
Risks With Severe Weight Loss
• Dehydration
– Fasting, extreme caloric restriction  water loss
– 2 to 4% weight loss as water  impaired
performance
– Risk of kidney, cardiovascular dysfunction, death
• Chronic fatigue
– Underweight  fatigue   performance, injury
– Mimics overtraining and chronic fatigue syndromes
– Underweight  substrate depletion
Body Composition in Sport:
Risks With Severe Weight Loss
• Eating disorders
– Weight standards can  disordered eating
– Anorexia nervosa, bulimia nervosa
– More prevalent with women in lean sports
• Menstrual dysfunction
– Delayed menarche, oligomenorrhea, or amenorrhea
– Prevalent in low-body-weight sports
– Due to caloric intake < caloric expenditure
Body Composition in Sport:
Risks With Severe Weight Loss
• Bone mineral loss
– Serious consequence of athletic amenorrhea
– Anorexia  fracture rate 7 times higher
• Female athlete triad
– Eating + menstrual + bone mineral disorders
– Seen with women in lean-physique, low-bodyweight, or endurance sports
– Skating, dance, gymnastics, running, swimming
Body Composition in Sport:
Weight Standards
• Appropriate weight standards
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Inappropriate standard risks athlete health
Body composition, not total body weight
Optimal range of percent body fat
Account for sex differences
• Weight standards not always appropriate
– Technical measurement errors
– Not all athletes perform best at ideal composition
Table 15.1
Body Composition in Sport:
Achieving Optimal Weight
• Avoid fasting and crash diets
– Cause more water and muscle loss, less fat loss
– Ketosis accelerates water loss
• Optimal weight loss:  fat mass,  FFM
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Moderate caloric restriction + exercise
Caloric deficit ~200 to 500 kcal/day
Lose no more than 0.5 to 1 kg/week
When near goal, slow weight loss further
Nutrition and Sport
• Recommended macronutrient balance
– Carbohydrate: 55 to 60% of daily kilocalories
– Fat: <35% (<10% saturated)
– Protein: 10 to 15%
• Optimal for both performance and health
Nutrition and Sport:
Classification of Nutrients
• Recommended Daily Allowance (RDA)
– Outdated—not bad, just insufficient
– Estimated safe, adequate dietary intakes and
minimum vitamin and mineral requirements
• Daily Recommended Intake (DRI)
– Current standard
– Groups intakes by nutrient function, classification
– Four reference values: EAR, RDA, UL, AI
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
Nutrition and Sport:
Classification of Nutrients—CHO
• 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
Nutrition and Sport:
Classification of Nutrients—CHO
• GI not perfect
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Individual GI response varies
Some complex CHOs have high GI
Fat + high GI = lower GI
GI calculations differ depending on reference food
(glucose vs. white bread)
• Glycemic load (GL)
– Improved CHO index
– GL = (GI x CHO, g)/100
Nutrition and Sport:
Classification of Nutrients—CHO
• CHO factors that  exercise time
– Normoglycemia, low-GI preexercise snack
– CHO loading (1-3 days prior)
– CHO feedings during exercise
• CHO factors that  exercise time
– Hypoglycemia, high-GI preexercise snack
– No CHO loading (lower glycogen stores)
– No CHO feeding during exercise
Figure 15.10
Figure 15.11
Nutrition and Sport:
Classification of Nutrients—CHO
• CHO during exercise
– Unlike preexercise CHO, does not trigger
hypoglycemia
– Improved muscle permeability to glucose?
– Insulin-binding sites altered during exercise?
• CHO intake after exercise essential
– Glycogen resynthesis high <2 h after exercise
– Protein + CHO intake enhances glycogen stores
– Stimulates muscle tissue repair
Figure 15.12
Nutrition and Sport:
Classification of Nutrients—Fat
• Fat essential for body function
– Fuel substrate (triglycerides  FFAs + glycerol)
– Component of cell membranes and nerve fibers
– Required by steroid hormones and fat-soluble
vitamins
• Saturated versus unsaturated FFAs
– Total fat <35% of total daily kilocalories (0 trans fat)
– Saturated fat <10% total daily kilocalories
– Cholesterol <300 mg/day
Nutrition and Sport:
Classification of Nutrients—Fat
• FFAs important fuel during exercise
– Delay exhaustion after glycogen depletion
– Body cannot metabolize triglycerides (dietary fat)
– Must break down triglycerides into FFAs
• High-fat versus high-CHO diets
– High-fat intake   circulating FFAs (good)
– High-fat intake   glycogen storage (bad)
– No conclusive evidence on high-fat diets
Nutrition and Sport:
Classification of Nutrients—Protein
• 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
• 20 amino acids: essential versus
nonessential
• Protein consumption
– 15% of total daily kilocalories
– ~0.80 g protein/kg body weight per day
Table 15.2
Nutrition and Sport:
Classification of Nutrients—Protein
• Protein requirements higher for athletes
– 1.2 to 1.7 g protein/kg body weight per day
– Endurance training: may use as fuel substrate
– Strength training: needed for building muscle
• Excessive protein intake  health risks
• CHO + protein after exercise  improved
glycogen and muscle protein synthesis
Nutrition and Sport:
Classification of Nutrients—Vitamins
• Small but essential organic molecules
– Enable use of other ingested nutrients
– Act as catalysts and cofactors in chemical reactions
• 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
Nutrition and Sport:
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
Nutrition and Sport: 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
Nutrition and Sport:
Classification of Nutrients—Minerals
• Minerals
– Inorganic substances needed for cellular function
– Macrominerals versus microminerals (trace
elements)
• Calcium
– Bone density, nerve and muscle function
– Concerns: osteopenia, osteoporosis
• Phosphorus
– Bound to calcium in bones
– Important for metabolism, cell membranes, buffers,
bioenergetics
Nutrition and Sport:
Classification of Nutrients—Minerals
• Iron
– Critical for hemoglobin, myoglobin (O2 transport)
– Deficiency  anemia
– Excess iron  toxicity
• 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 dangerous
Nutrition and Sport:
Classification of Nutrients—Water
• 50 to 60% of total body weight
– Fat-free mass 73% water versus fat mass 10%
water
– 1 to 6% body weight loss in sweat common for
athletes
– 9 to 12% loss can be fatal
– 2/3 body water intracellular, 1/3 extracellular
• Medium for transportation, diffusion
• Regulates temperature
• Maintains blood pressure
Nutrition and Sport:
Water and Electrolyte Balance
• Water gain at rest (33 ml/kg/day)
– 60% from beverages
– 30% from food
– 10% from cellular respiration
• Water loss at rest
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Evaporation from skin, respiratory tract (30%)
Excretion from kidneys (60%)
Excretion from large intestine (5%)
Sweat (5%)
Nutrition and Sport:
Water and Electrolyte Balance
• Dehydration during exercise
– Sweat  due to higher body temperature
– Water loss > water gain
• Body temperature and sweating affected by
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Environmental temperature, radiant heat load
Humidity
Air velocity
Body size
Metabolic rate
Table 15.4
Figure 15.13
Nutrition and Sport: Dehydration
and Exercise Performance
• Impairs aerobic performance
–  Temperature   sweat loss   performance
–  Plasma volume   cardiovascular function
–  Plasma volume   thermoregulatory function
• Effect of dehydration on anaerobic and
strength performance unclear
Figure 15.14
Nutrition and Sport: Dehydration
and Exercise Performance
• Electrolyte loss in sweat
– Sweat similar to (and derived from) plasma
– Mostly Na+, Cl- (concentrations will vary)
– Remaining ions in body must redistribute
• Electrolyte loss in urine
– Kidneys regulate electrolyte excretion
–  Urine production =  electrolyte excretion
– Aldosterone  Na+ retention   thirst and drinking
Table 15.5a
Table 15.5b
Table 15.6
Nutrition and Sport: 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 during exercise
– Minimize dehydration and water loss
– Performance and cardiovascular function maintained
Figure 15.15
Nutrition and Sport: Dehydration and
Exercise Performance
• Hyponatremia
– Serum Na+ <135 mmol/L
– Excessive Na+ loss + excessive rehydration
– Relatively rare (e.g., ultramarathoners)
• Symptoms
– Mild: bloating/puffiness, nausea/vomiting, headache
– More severe: cerebral edema, cognitive/central
nervous system dysfunction, pulmonary edema,
coma, death
Nutrition and Sport:
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
• Precompetition meal
– 200 to 500 kcal at least 2 h before competition
– Mostly CHOs: cereal, milk, juice, toast
– Liquid meals
Nutrition and Sport:
The Athlete’s Diet
• Maximal glycogen stores   performance
• Carbohydrate (glycogen) loading
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Tapering training week before event
Days 6 to 4 before event: normal CHO diet
Days 3 to 1 before event: high CHO diet
Muscle glycogen stores doubled
Figure 15.16
Nutrition and Sport:
The Athlete’s Diet
• Diet prepares liver for endurance exercise
– CHO loading greatly increases liver glycogen,
reduces hypoglycemia
– 1 g glycogen stored with 2.6 g water
– CHO loading  glycogen  water weight gain
• Back-to-back competition
– Liver glycogen resynthesized quickly
– Muscle glycogen resynthesized slowly
–  CHO + protein intake <2 h after competition
Figure 15.17
Nutrition and Sport:
Sport Drinks
• Composition of sport drinks
– Water + energy (CHO) + electrolytes
– Widespread performance benefits
• CHO concentration: energy delivery
–  CHO content slows gastric emptying
– Most drinks have 6 to 8 g CHO per 100 ml fluid
– Mostly glucose, glucose polymers
Nutrition and Sport:
Sport Drinks
• Na+ concentration: aids rehydration
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Glucose and Na+ stimulate water absorption
Na+   thirst and palatability
Na+ retention promotes water retention
20 to 60 mmol/L
• What works best?
– Light flavor, no strong aftertaste
– Taste, composition   ad libitum consumption