Sports Nutrition Chapter 14

Nutrition and Physical Performance Cardiorespiratory fitness Muscular strength Muscular endurance

Guidelines for Physical Activity

Energy Systems, Muscles, and Physical Performance ATP–CP energy system Quick source of ATP Cellular ATP and creatine phosphate Fuel for 3–15 seconds of maximal effort

Energy Systems, Muscles, and Physical Performance Lactic acid energy system Breakdown of glucose to lactic acid (lactate) Doesn’t require oxygen Rise in acidity triggers muscle fatigue

Energy Systems, Muscles, and Physical Performance Oxygen energy system Breakdown of carbohydrate and fat for energy Requires oxygen Produces ATP more slowly

Energy Systems, Muscles, and Physical Performance Teamwork in energy production Anaerobic systems for short duration activities, early part of endurance activities Aerobic systems for endurance activities Training Decreases reliance on anaerobic systems Extends availability of glycogen

Energy Systems, Muscles, and Physical Performance Glycogen Depletion Initial, primary energy source with gradual depletion “Hit the wall” Endurance Training Enhances aerobic capacity Decreases reliance on anaerobic energy system

Muscles and Muscle Fibers Slow-twitch (ST) fibers Breakdown carbohydrate and fat via aerobic pathways Fast-twitch (FT) fibers Anaerobic pathways Fiber type and the athlete Genetics

Optimal Nutrition for Athletic Performance Underlying foundations are similar to the basic principles in the Dietary Guidelines for Americans Differences Increase fluid needs Increase energy needs

Energy Intake and Exercise Priority = Adequate energy intake by eating small, frequent meals Maintain metabolism Improve nutrient intake Achieve desirable body composition Support a training schedule Reduce injuries

Carbohydrate and Exercise High-carbohydrate diets Increase glycogen stores Extend endurance Carbohydrate loading Carbohydrate intake Before exercise During exercise Following exercise

Dietary Fat and Exercise Major fuel source during exercise High-fat diet not needed Recommendations Moderate fat intake with focus on monounsaturated and polyunsaturated sources © ZUMA Press, Inc./Alamy

Protein and Exercise Protein recommendations Adults: 0.8 grams/kg body weight Endurance athletes: 1.2–1.4 grams/kg Strength athletes: 1.6–1.7 grams/kg Protein sources Foods: lean meats, fish, low-fat dairy, egg whites Protein intake after exercise Helps replenish glycogen Dangers of high protein intake diuresis

Vitamins, Minerals, and Athletic Performance B vitamins Needed for energy metabolism Choose variety of whole grains, fruits, vegetables Calcium Needed for normal muscle function, strong bones Low-fat dairy products Adequate intake may be a problem for females

Vitamins, Minerals, and Athletic Performance Iron Needed for oxygen delivery and energy production Athletes have higher losses Lean red meats, vegetables, enriched grains Other Trace Minerals Copper zinc

Fluid Needs During Exercise Exercise and fluid loss Increased losses from sweat Increased with heat, humidity Risk for dehydration Hydration Adequate fluids before, during, after exercise Water vs. sports drinks

Nutrition Needs of Young Athletes Short stature and delayed puberty Nutrient deficiencies and dehydration Menstrual irregularities Poor bone health Increases incidence of injuries Increased risk of developing eating disorders

Nutrition Supplements and Ergogenic Aids Most are unnecessary for athletes who select a variety of foods and meet their energy needs Although some have been well researched, most lack vigorous clinical trials

Nutrition Supplements and Ergogenic Aids Regulation and concerns about dietary and herbal supplements Dietary Supplement Health and Education Act Contamination of products Purchases from other countries May contain substances not shown on the package label

Nutrition Supplements and Ergogenic Aids: Types Convenience supplements Weight gain powders Amino acids Branched chain amino acids HMB Glutamine Creatine Antioxidants

Nutrition Supplements and Ergogenic Aids: Types Caffeine Sodium bicarbonate Iron Beta-alanine

Weight and Body Composition Weight gain Build Muscle, Lose Fat Weight loss Lose fat, maintain muscle Avoid dangerous weight loss practices Female athlete triad Disordered eating Amenorrhea Premature osteoporosis Breaking the triad

Slow-Twitch Fibers With a sufficient supply of oxygen, slow-twitch (ST) fibers can maintain muscular activity for a prolonged time. This ability is known as aerobic endurance. Because ST fibers have high aerobic endurance, your body predominantly relies on them during low-intensity endurance events, such as a marathon, and during everyday activities, such as walking.

Fast-Twitch Fibers Compared to slow-twitch fibers, fast-twitch (FT) fibers have poor aerobic endurance. They are optimized to perform anaerobically (when the oxygen supply is limited). The body recruits both ST and FT fibers during shorter, higher-intensity endurance events, such as the mile run or the 400-meter swim.

Pound for Pound? Women’s muscles have smaller muscle fiber cross sections and less muscle mass then men. For a given amount of muscle, however, there is no difference in strength between men and women.

Structure of Skeletal Muscle

Fiber Type and the Athlete Genes determine the relative proportion of muscle fiber types in athletes. Although distance runners who have a high percentage of ST fibers are well suited for endurance events, they will not succeed as elite sprinters. Conversely, sprinters who have predominantly FT fibers are better equipped for explosive events, but they will not become competitive marathon runners.

Fat Intake and the Athlete Fat intake should not be overly restricted. There is no performance benefit in consuming a diet with less than 15 percent of energy from fat. Extreme fat restriction limits food choices, especially sources of protein, iron, zinc, and essential fatty acids. Sports nutritionists recommend that any extra fat calories come from monounsaturated and polyunsaturated sources.

Making Weight Wrestlers, weight lifters, boxers, jockeys, rowers, and coxswains face competitive pressures to “make weight” to compete or to be certified in a lower weight classification. In order to make weight, such athletes often resort to pathogenic weight-control behaviors such as fasting, using diet pills, following a fat-free diet, using diuretics or laxatives, or excessive exercise. Repeated cycles of rapid weight loss and subsequent regain increase risk of disordered eating, fatigue, psychological distress (anger, anxiety, depression), dehydration, and sudden death.

Glycogen Depletion and Fatigue Sensation

American Heart Association: Physical Activity Physical inactivity is a major risk factor for developing coronary artery disease. Even moderately intense physical activity such as brisk walking is beneficial when done regularly for a total of 30 minutes or longer most days.