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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.