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Transcript
chapter
14
Body Composition
and Nutrition for
Sport
Body Build, Size, and Composition
Body build is the form or structure of the body.
• Muscularity
• Linearity
• Fatness
Body size is determined by height and weight.
Body composition refers to the chemical composition
of the body
• Fat mass
• Fat-free mass
Three Models of Body Composition
Adapted, by permission, from J.H. Wilmore, 1992, Body weight and body composition. In Fasting, body
weight, and performance in athletes: Disorders of modern society, edited by R. Brownell and J.H. Wilmore
(Baltimore, MD: Lippincott, Williams, and Wilkins), 77-93.
Did You Know . . . ?
Fat-free mass is composed of all of the body’s nonfat
tissue, including bone, muscle, organs, and
connective tissue. Lean body mass includes all fatfree mass along with essential fat. Lean body mass
is difficult to measure, so the fat mass/fat-free mass
model is most often used.
Did You Know . . . ?
Body composition is a better indicator of fitness than
body size and weight. Being overfat (not necessarily
overweight) has a negative impact on athletic
performance. Standard height–weight tables do not
provide accurate estimates of what an athlete should
weigh because they do not take into account the
composition of the weight. An athlete can be
overweight according to those tables yet have very
little body fat.
Assessing Body Composition
• Densitometry (hydrostatic weighing)
• Skinfold fat thickness
• Bioelectric impedance
Densitometry
• Body density = Body mass ÷ Body volume
• Body mass = measured on a regular scale
• Body volume = measured using hydrostatic
(underwater) weighing accounting for
water density and air trapped in the
lungs
• % body fat = (495 ÷ body density) – 450
Underwater Weighing Technique to
Determine Density of the Body
Tom Pantages
UNDERWATER WEIGHING TECHNIQUE
Dual-Energy X-Ray Absorptiometry
Machine
Photo courtesy of Hologic, Inc.
Bod Pod device
Photo courtesy of Life Measurement, Inc.
Measuring Skinfold Fat Thickness at
the Triceps Skinfold Site
© Human Kinetics
Bioelectric Impedance Technique for
Assessing Relative Body Fat
© Human Kinetics
Did You Know . . . ?
Inaccuracies in densitometry are due to the variation
in the density of the fat-free mass from one individual
to another. Age, sex, and race affect the density of fatfree mass.
Body Composition and
Performance
Maximizing Fat-Free Mass
• Desirable for strength, power, and muscular
endurance
• Undesirable for endurance or jumping sports if the
result is weight gain
Minimizing Relative Body Fat
• Desirable, especially in sports in which the body
weight is moved through space
• Improves speed, endurance, balance, agility, and
jumping ability
Relative Body Fat in Elite Female
Track and Field Athletes
Data from J.H. Wilmore et al., 1977, “Body physique and composition of the female distance runner,” Annals of the New York
Academy of Sciences 301: 764-776.
Risks With Severe Weight Loss
•
•
•
•
•
Dehydration
Chronic fatigue
Disordered eating and eating disorders
Menstrual dysfunction
Bone mineral disorders
COMPOSITION OF WEIGHT LOSS
Appropriate Weight Guidelines
• Maximize performance within the specific sport
(See table 14.1, page 327)
• Are based on body composition
• Emphasize relative body fat rather than total body mass
• Use a range of relative fat values that are considered
acceptable for the athlete’s age and sex
Achieving Optimal Weight
• Combine proper diet with exercise.
• Lose no more than 1.0 kg (2 lb) per week.
• Reduce caloric intake to 200 to 500 kcal less than daily
energy expenditure.
• Use moderate resistance and endurance training.
Six Nutrient Classes
•
•
•
•
•
•
Carbohydrate
Fat
Protein
Vitamins
Minerals
Water
Recommended Balance of Nutrients
• 55% to 60% carbohydrate
• Less than 30% fat (less than 10% saturated)
• 10% to 15% protein
Carbohydrate (CHO)
• Provides energy, particularly during high-intensity
exercise
• Regulates fat and protein metabolism
• Exclusive energy source for the nervous system
• Synthesized into muscle and liver glycogen
• Sources include grains, fruit, vegetables, milk, and sweets
• Glycemic index influences performance and health
Influence of Dietary Carbohydrate (CHO)
on Muscle Glycogen Stores During
Repeated Days of Training
D.L. Costill and J.M. Miller, "Nutrition for endurance sport: Carbohydrate and fluid balance," 1980,
International Journal of Sports Medicine 1: 2-14. Reprinted by permission.
Relationship Between Preexercise Muscle
Glycogen Content and Exercise Time to
Exhaustion
D.L. Costill and J.M. Miller, "Nutrition for endurance sport: Carbohydrate and fluid balance," 1980,
International Journal of Sports Medicine 1: 2-14. Reprinted by permission.
CHO Types
Simple Sugar
• Elevates blood glucose levels
• Relies on insulin to move it to cells
• When intake exceeds usage, stored within the cells
as fat
Complex CHO
• Requires more time to break down
• Produces a smaller and slower rise in blood glucose
• Has less impact on blood lipid levels
Key Points
Ergogenic Properties of CHO
• Muscle glycogen loading may delay onset of
fatigue.
• Maintaining normal blood glucose levels may allow
the muscles to obtain more energy from blood
glucose, sparing liver and muscle glycogen
reserves.
• Activities over 1 hour can be enhanced when
carbohydrate is consumed within 5 minutes of, over
2 hours before, and at frequent intervals during the
activity.
Influence of Exercise Intensity (%VO2)
on Muscle Glycogen Stores
Adapted, by permission, from A. Jeukendrup and M. Gleeson, 2004, Sport nutrition: An introduction to
energy production and performance (Champaign, IL: Human Kinetics) . Original data from Gollnick, Piehl,
and Saltin.
CHO INTAKE AND PERFORMANCE
Effects of Preexercise Carbohydrate
Feeding on Blood Glucose Levels During
Exercise
Adapted, by permission, from D.L. Costill et al., 1977, "Effects of elevated plasma FFA and insulin on
muscle glycogen usage during exercise," Journal of Applied Physiology 43(4): 695-699.
Replenishment of Muscle Glycogen Stores
Using Two Different Regimens of
Carbohydrate Replacement
Adapted, by permission, from J.L. Ivy et al., 1988, "Muscle glycogen synthesis after exercise: Effect of time of carbohydrate
ingestion," Journal of Applied Physiology 64: 1480-1485.
Did You Know . . . ?
Carbohydrate intake during exercise does not produce
the same hypoglycemic effects as preexercise intake.
This difference may be caused by increased muscle
fiber permeability that decreases the need for insulin
during exercise, or insulin-binding sites may be
altered during muscular activity.
Fat
•
•
•
•
•
•
Makes up cell membranes and nerve fibers
Provides up to 70% energy at rest
Cushions vital organs
Produces all steroid hormones
Transports and stores fat-soluble vitamins
Preserves body heat
Key Points
Ergogenic Properties of Fat
• Use of FFAs for energy production can delay
exhaustion.
• Chronic endurance training results in more
reliance on fat for energy.
• For some individuals, caffeine promotes fat use
and improves performance.
Protein
•
•
•
•
•
•
•
Makes up cell structure
Provides up to 10% energy during exercise
Produces hemoglobin, enzymes, and many hormones
Maintains normal blood osmotic pressure
Forms antibodies
Can be energy source
Breaks down into amino acids to be used by the body
Key Points
Ergogenic Properties of Protein
• Builds fat-free muscle mass.
• Strength athletes need 1.4 to 1.8 g per kg body
weight.
• Endurance athletes need 1.2 to 1.4 g per kg body
weight.
• Diets exceeding 2.0 g per kg body weight per day
have not been proven to provide additional
benefits and may damage kidney function.
Vitamins
Fat Soluble
• A, D, E, and K
• Absorbed from digestive tract and bound to lipids
• Excessive intake can cause toxic accumulations
Water Soluble
• B-complex and C
• Absorbed from digestive tract with water
• Excess is excreted
B-Complex Vitamins
• Include more than 1 dozen vitamins
• Involved in energy production
• If deficiency, supplementation may facilitate performance
Vitamin C
• Formulates and maintains collagen in connective tissue
• Helps metabolize amino acids
• Helps synthesize epinephrine, norepinephrine, and
corticoids
• Promotes iron absorption
• May help fight infection and function as antioxidant
• Supplementation does not appear to improve
performance if no deficiency exists
Vitamin E
•
•
•
•
•
Stored in muscle and fat
Prevents oxidation of vitamins A and C
Acts as antioxidant to disarm free radicals
May decrease risk of coronary artery disease
Supplementation has not been proven to improve
performance
Minerals
Electrolytes are mineral compounds that can
dissociate into ions in the body.
Macrominerals are minerals that your body needs 100
g of per day.
Microminerals are minerals that your body needs less
than 100 g of per day.
Calcium
•
•
•
•
•
Most abundant mineral in the body
Stored in the bones
Facilitates bone growth and maintenance
Essential in nerve impulse transmission
Activates enzymes and regulates cell membrane
permeability
• Essential for normal muscle function
Phosphorus
•
•
•
•
•
Commonly linked to calcium in form of calcium phosphate
Provides strength and rigidity to bones
Essential to metabolism and component of ATP
Part of cell membrane structure
Helps maintain constant blood pH
Iron
• Helps form hemoglobin and myoglobin
• Deficiency is relatively common, more so in women
• If deficiency, supplementation can improve aerobic
capacity
Sodium, Potassium, and Chloride
• Separate electrical charge across neuron and muscle cell
membranes
• Maintain body’s water balance and distribution
• Maintain normal osmotic equilibrium and pH
• Maintain normal cardiac rhythm
Did You Know . . . ?
Vitamins and minerals do not appear to have any
ergogenic value in amounts beyond the RDA. Taking
them in amounts greater than RDA will not improve
performance and may be dangerous.
Water
• Makes up blood plasma, which transports and delivers
nutrients to tissues
• Makes up body fluids that regulate pH
• Dissipates excess body heat during exercise
• Maintains blood pressure
BODY WATER AT REST
Key Points
Water Balance During Exercise
• Metabolic water production increases as body heat
increases.
• Water loss increases during exercise due to
sweating.
• Blood flow to the kidneys decreases to prevent
dehydration.
• If dehydration exceeds 2% body weight, physical
performance is impaired.
Decline in Running Velocity With
Dehydration of About 2% of Body Weight
Reprinted, by permission, from L.E. Armstrong, D.L. Costill, and W.J. Fink, 1985, "Influence of diureticinduced dehydration on competitive running performance," Medicine and Science in Sports and Exercise 17:
456-461.
Key Points
Electrolyte Balance During Exercise
• Loss of water via sweating disrupts
electrolyte balance.
• Sodium and chloride are the most abundant
electrolytes in sweat.
• Excess electrolytes are excreted in the urine
during rest, but less so during exercise.
• Dehydration causes aldosterone to promote
renal retention of sodium and chloride ions,
raising their concentrations in the blood.
This, in turn, triggers thirst.
Effects of 6 h of Treadmill Running in
the Heat on Heart Rate
Data from S.I. Barr, D.L. Costill, and W.J. Fink, 1991, "Fluid replacement during prolonged exercise: Effects
of water, saline or no fluid," Medicine and Science in Sports and Exercise 23: 811-817.
Key Points
Replacing Fluid Losses
• The need to replace body fluids is greater than the
need to replace electrolytes.
• The thirst mechanism does not match the
hydration state, so it is best to consume more fluid
than thirst dictates.
• Water intake during prolonged exercise reduces
the risk of dehydration and optimizes performance.
• Drinking too much fluid can result in hyponatremia
(low levels of plasma sodium), which can cause
confusion, disorientation, and seizures.
(continued)
Key Points (continued)
The Athlete’s Diet
• There is no one typical diet of an athlete; but it is
important that athletes and active people alike
meet their RDA of nutrients.
• Athletes can get the nutrition they need with a
strictly vegetarian diet as long as the foods they
select include a balance of essential nutrients and
calories.
• The precompetition meal can ensure a normal
blood glucose level and prevent hunger; it should
include 200 to 500 kcal of foods that are easily
digestible and are eaten no less than 2 hours
before competition.
Åstrand’s Glycogen Loading
1. Complete an exhaustive training bout 7 days before
event.
2. Eat fat and protein for next 3 days and reduce training
load; this increases glycogen synthesis.
3. Eat a carbohydrate-rich diet for remaining 3 days
before event and reduce training load; because of
increased glycogen synthesis, more glycogen is
stored.
Sherman’s Glycogen Loading
7 Days Before Competition
• Reduce training intensity.
• Eat a normal, healthy mixed diet with 55%
carbohydrate.
3 Days Before Competition
• Reduce training to daily warm-up of 10 to 15
minutes.
• Eat a carbohydrate-rich diet.
Two Regimens for Muscle Glycogen
Loading
Data from P.-O. Astrand, 1979, Nutrition and physical performance. In Nutrition and the world food problem,
edited by M. Rechcigl et al. (Basel, Switzerland: S. Karger).
Muscle Glycogen Resynthesis
Effects of Solution Characteristics
on the Rate of Gastric Emptying
Solution characteristic
Rate of emptying
Volume of the solution
Increases with larger volumes
Caloric content
Decreases as the caloric density
increases
Osmolarity
Decreases with hyperosmolar
solutions
Temperature
Faster for cooler fluids than
warm solutions
pH
Decreases with more acidic
solutions
Gastric Emptying
•
•
•
•
•
.
Slows at exercise intensities above 70% VO2max
Is the same .rate at rest as it is at exercise intensities
below 70% VO2max
Affected by an individual’s fitness—the more fit, the
less exercise affects it
Not affected by exercise duration
Affected differently by different types of activities
CHO AND RATE OF GASTRIC EMPTYING
Key Points
Designing Sport Drinks
• Fructose, glucose, and maltodextrin may empty
fastest from digestive tract.
• Concentrations less than 11 g of CHO per 100 ml
empty faster but don’t supply the full energy needed
for prolonged exercise.
• Athletes prefer a drink with a light flavor and no
strong aftertaste.
• During prolonged exercise, water intake is primary,
but drinking 4 g to 8 g of CHO per 100 ml solution
every 10 to 15 minutes reduces dehydration and
provides a partial energy supplement.