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C H A P T E R 13 NUTRITION AND SPORT
w Learn how dehydration affects performance, heart rate, and body temperature. (continued) Learning Objectives w Review the six categories of nutrients and learn what amount of intake is necessary for normally active men and women. w Discover the roles of carbohydrate, dietary fat, and protein supplements in athletic performance. w Find out which vitamins and minerals are most important in an athlete’s diet.
Learning Objectives w Examine how the body regulates electrolyte balance during exercise and maximizes muscle glycogen storage. w Find out what makes up a recommended precompetition meal and how to properly load the muscles with glycogen before an endurance event. w Learn the value of ingesting carbohydrates during and after endurance exercise and what constitutes the most effective sports drink.
Days precompetition before during after general before meal exercise exercise exercise training exercise * A healthy/optimal diet is context specific and may be quite different between a sedentary person and someone who is training
Six Nutrient Classes w Carbohydrate w Fat w Protein w Vitamins w Minerals w Water
Recommended Balance of Nutrients w 55% to 60% carbohydrate w Less than 30% fat (less than 10% saturated) w 10% to 15% protein
Carbohydrate (CHO) w Provides energy, particularly during high-intensity exercise w Regulates fat and protein metabolism w Exclusive energy source for the nervous system w Synthesized into muscle and liver glycogen w Sources include grains, fruit, vegetables, milk, and sweets
Simple sugars • In general, rapidly elevate blood glucose levels – high glycemic index – which causes large secretion of insulin w When intake exceeds usage, may be stored within the cells as fat, particularly in adipocytes (very costly, does not happen to any great extent) Complex CHOs • Generally require more time to breakdown (lower glycemic index), therefore causing more moderate elevation in insulin secretion w Have less impact on blood lipid levels CHO Types
High GI foods (GI >85) Soft drinks, honey/syrups, ice cream, whole wheat bread, raisins, potatoes, carrots, beer Moderate GI foods (GI 60-85) Pastry, pita bread, white rice, orange, popcorn, banana, low-fat ice cream Low GI foods (GI <60) Spaghetti, milk, grapefruit, beans, apples, pears, peanuts, and yogurt Glycemic Index (GI) The glycemic response to carbohydrate varies depending on the food
Key Points Ergogenic Properties of CHO w Glycogen loading the muscles may delay onset of fatigue. w Maintaining normal blood glucose levels may allow the muscles to obtain more energy from blood glucose, sparing liver and muscle glycogen reserves. w 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.
° Astrand’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 the activity of glycogen synthase in response to low muscle glycogen. 3. Eat a CHO-rich diet for remaining 3 days before event and reduce training load; because of increased glycogen synthesis, more glycogen is stored.
7 days before competition w Reduce training intensity w Eat a normal, healthy mixed diet with 55% CHO 3 days before competition w Reduce training to daily warm-up of 10 to 15 minutes w Eat a CHO-rich diet Sherman’s Glycogen Loading
CHO INTAKE AND PERFORMANCE CHO and placebo drinks were taken every 15 min during exercise
PRE-EXERCISE CHO FEEDING Hypoglycemia
Hypoglycemic Effect during Exercise? Carbohydrate intake during exercise does not produce the same hypoglycemic effects as pre-exercise intake. This difference may be caused by increased muscle fiber glucose uptake during muscle contraction that decreases the need for insulin during exercise, or insulin-binding sites may be altered during muscular activity.
Fat w Important constituent of cell membranes and nerve fibers (myelin sheath) w Provides up to 70% energy at rest w Cushions vital organs w Used to produce steroid hormones (cholesterol) w Transports and stores fat-soluble vitamins w Helps preserve body heat (provides insulation)
Fat Milk type Weight H2O Energy (8 oz) (g) (% weight) (kcal) (g) (% weight) (kcal) (% kcal) Whole 244 88 150 8.15 3.3 73.4 48.9 2% low-fat 244 89 121 4.78 2.0 43.0 35.6 1% low-fat 244 90 102 2.54 1.0 22.9 22.4 Skim 245 91 86 0.44 0.2 4.0 4.6 Calculating the Fat Content of Foods
Key Points Ergogenic Properties of Fat w Use of FFAs for energy production can delay exhaustion during exercise. w Chronic endurance training results in more reliance on fat for energy. w For some individuals, caffeine promotes fat use and improves performance.
Protein w Required for development, repair, and maintenance of cells w Main constituent of hemoglobin, enzymes, and many hormones w Helps maintain normal blood osmotic pressure w Used to form antibodies w Can be energy source, but it is a minor contributor except during fasting or starvation w Made up of 20 amino acids (9 essential and 11 nonessential)
Essential Nonessential Isoleucine Alanine Leucine Arginine Lysine Asparagine Methionine Aspartic acid Phenylalanine Cysteine Threonine Glutamic acid Tryptophan Glutamine Valine Glycine Histidine (children)a Proline Serine Tyrosine Histidine (adult)* aHistidine is not synthesized in infants and young children, so it is an essential amino acid for children but not for adults. Essential and Nonessential Amino Acids
Key Points Ergogenic Properties of Protein w Builds fat-free muscle mass. w Strength athletes need 1.4 to 1.8 g per kg body weight versus 0.8 g per kg RDA. w Endurance athletes need 1.2 to 1.4 g per kg body weight versus 0.8 g per kg RDA. w Diets exceeding 1.8 to 2.0 g per kg body weight per day have not been proven to provide additional benefits and may damage kidney function. Also, excess protein may be converted to fat. w Supplements are generally not needed providing caloric intake is adequate.
Fat soluble w A, D, E, and K w Absorbed from digestive tract and bound to lipids w Excessive intake can cause toxic accumulations Water soluble w B-complex and C w Absorbed from digestive tract with water w Excess is excreted Vitamins
B-Complex Vitamins w Include more than 1 dozen vitamins w Important components of enzymes involved in energy production wIf deficient in the diet, supplementation may facilitate performance
Vitamin C w Synthesis and maintenance of collagen in connective tissue w Helps metabolize amino acids w Helps synthesize epinephrine, norepinephrine, and corticoids w Promotes iron absorption w May help fight infection and function as an antioxidant • Supplementation does not appear to improve performance if no deficiency exists • Sever deficiency results in scurvy (why were British sailors called “limeys”?)
Vitamin E w Stored in and fat, including cell membranes w Prevents oxidation of vitamins A and C w Acts as an antioxidant to disarm free radicals w May decrease risk of coronary artery disease and cancer w Supplementation has not been proven to improve performance
Minerals Electrolytes—mineral compounds that can dissociate into ions in the body Macrominerals—minerals that your body needs ≥ 100 mg of per day Microminerals—minerals that your body needs less than 100 mg of per day
Calcium w Most abundant mineral in the body; second most common mineral deficiency (behind iron) w Stored in the bones w Facilitates bone growth and maintenance w Essential in nerve impulse transmission w Activates enzymes and regulates cell membrane permeability w Essential for normal muscle function
Phosphorus w Commonly linked to calcium in form of calcium phosphate w Provides strength and rigidity to bones w Essential to metabolism and component of ATP w Part of cell membrane structure (phospholipids) w Helps maintain constant blood pH
Iron w Essential component of hemoglobin and myoglobin; O2 specifically binds to the Fe2+ in the proteins • Deficiency is relatively common, more so in women because of menstruation and tendency of women to eat less • Estimated ~25% of world’s population has iron-deficiency anemia – most common mineral deficiency w If deficiency, supplementation can improve aerobic capacity
Sodium, Potassium, and Chloride w Separation across neuron and muscle cell membranes results in the membrane potential w Maintain body's water balance and distribution w Maintain normal osmotic equilibrium and pH w Maintain normal cardiac rhythm
The Rule of Thumb Vitamins and minerals do not appear to have any ergogenic value in amounts beyond the recommended daily allowance (RDA), which is achieved by eating a good, balanced diet. Taking them in amounts greater than RDA will not improve performance and may be dangerous.
Body Water – Intracellular (67%) and Extracellular (33%) - ~60% of body mass is water w Makes up blood plasma, which transports and delivers nutrients to tissues w Body fluids regulate pH w Dissipates excess body heat during exercise w Maintains blood pressure
Rest Prolonged exercise Source of loss ml/h % total ml/h % total Insensible loss skin 14.6 15 15 1.1 respiration 14.6 15 100 7.5 Sweating 4.2 5 1,200 90.6 Urine 58.3 60 10 0.8 Feces 4.2 5 — 0.0 Total 95.9 100 1,325 100 Comparison of Water Loss From the Body at Rest in a Cool Environment and During Prolonged Exhaustive Exercise
Key Points Water Balance During Exercise w Metabolic water production increases as metabolic rate increases—water gain. w Water loss increases during exercise due to sweating. w Blood flow is redistributed away from the kidneys which helps prevent dehydration —reduced urine output. w If dehydration exceeds 2% body weight, physical performance is impaired.
DEHYDRATION AND PERFORMANCE Effect of 2% dehydration on running velocity at 1500, 5000, and 10,000 meters
Key Points Electrolyte Balance During Exercise w Loss of water via sweating disrupts electrolyte balance. w Sodium and chloride are the most abundant electrolytes in sweat. w Excess electrolytes are excreted in the urine during rest, but less so during exercise. w Dehydration causes aldosterone to be released, which promotes renal retention of sodium and chloride ions, raising their concentrations in the blood. This, in turn, triggers thirst.
Electrolytes (mEq/L) OsmolaritySite Na+ Cl– K+ Mg2+ (mOsm/L) Sweat 40-60 30-50 4-6 1.5-5 80-185 Plasma 140 101 4 1.5 295 Muscle 9 6 162 31 295 Note. mEq/L = milliequivalents per liter (thousandths of 1 g of solute per 1 L of solvent). Electrolyte Concentrations and Osmolarity in Sweat, Plasma, and Muscle of Men Following 2 h of Exercise in the Heat
Fluid Replacement during Exercise in the Heat Saline (0.9% NaCl) or water were given equal to the weight loss during 6 hours of exercise in the heat These subjects became exhausted before completing the exercise
Key Points Replacing Fluid Losses wThe need to replace body fluids is greater than the need to replace electrolytes. wOur thirst mechanism does not match our hydration state, so it is best to consume more fluid than thirst dictates. w Water intake during prolonged exercise reduces the risk of dehydration and optimizes performance. w Drinking too much fluid can result in hyponatremia (low levels of plasma sodium), which can cause confusion, disorientation, and seizures; however, this is not a common problem.
Key Points Athlete’s Diets w There is no one typical diet of an athlete; yet, it is important that athletes and active people alike meet their RDA of nutrients. w 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. w 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.
Key Points Designing Sports Drinks wIn designing sports drinks, there is no clear advantage of using one type of CHO over another. w Concentrations less than 11 g of CHO per 100 ml empty faster, but don't supply the full energy needed for prolonged exercise. w Athletes prefer a drink with a light flavor and no strong aftertaste. w 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 risk of dehydration and provides a partial energy supplement.
5 g of glucose 10 g of glucose Water per 100 ml per 100 ml Variables Before Residue Before Residue Before Residue Osmolarity 23 87 266 245 532 434(mOsm/L) Sodium 0.7 7.9 1.5 18.6 1.9 14.5(mEq/L) Potassium 0.10 4.11 0.11 5.21 0.10 3.63(mEq/L) Glucose 0.0 0.0 5.0 3.3 10.0 6.5(g/100 ml) pH 4.76 2.05 3.50 2.29 3.46 2.40 Gastric — 32 — 52 — 65secretiona (ml) aGastric secretion denotes the volume of secretion calculated to be present in the residue. Composition of Water and Glucose Solutions before Ingestion and the Residues Remaining in the Stomach 20 Min after Ingestion of 100 ml