Perspectives in Nutrition 5 th ed. Gordon M.Wardlaw, PhD, RD, LD, CNSD PowerPoint Presentation by Dana Wu Wassmer, MS, RD

Chapter 14: Sports Nutrition

Benefits of Regular Physical Activity Cardiovascular health Maintains lean muscle tissue Reduces health risks associated with obesity Enhances insulin action Strengthens bone

Benefits of Regular Physical Activity Reduces susceptibility to infections Reduces cancers risk Improves peristaltic functions Fewer injuries Psychological health

Beginning an Exercise Program Start out slowly Vary your workout; make it fun Include others to help you keep accountable Set attainable goals Set aside specific time Reward yourself Focus on long-term and not on occasional setbacks

Fuel for Muscle Work ATP Chemical energy used by cells for muscle contractions Only a small amount is stored in resting cells (2-4 sec. of work) Other sources of energy are needed

Phosphocreatine (PCr) A high-energy compound that is formed and stored in the muscle cells PCr + ADP Cr + ATP Activated instantly and replenish ATP Not enough is stored or made in the muscle to sustain ATP for more than a few minutes

Anaerobic Glycolysis Limited oxygen to the muscle cells Intense physical activity (sprinting) Pyruvate is converted to lactate Produces 2 ATP per glucose (~5% of energy potential) Replenishes ATP quickly Provides energy for 30 seconds to 2 minutes of work Lactate build-up will change acidity and inhibit glycolysis enzymes

Glucose - The Major Fuel Aerobic glycolysis Plenty of oxygen available Low to moderate intensity (jogging) Produces ATP per glucose (95% of energy potential) Replenishes ATP slowly Provides energy for 2minutes to 3 hours of work

Glucose Utilization Glucose 2 Pyruvate Anaerobic Aerobic 2 ATP ATP Lactic Acid CO2 + H2O

Glycogen Temporary storage of glucose in the liver and muscle Muscle glycogen is used only by that muscle; liver glycogen is released into the blood stream Low to moderate intensity; sustain work for up to 2 hours Once depleted, can only work at ~50% of maximal capacity (“hitting the wall”)

Fuel Use During Various Activities (Fig. 14-3) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Maintaining Normal Blood Glucose Level For activity lasting longer than minutes Blood glucose is an important source of fuel Intake of gm CHO/hour is helpful during strenuous endurance activity Delays fatigue by minutes

Fat Fuel Majority of stored energy in the body Fatty acids can be converted to acetyl-CoA in the mitochondria of muscle cells Produces 12 ATP per turn of the Citric Acid Cycle (or 147 ATP per 18 C fatty acid chain) Trained muscles have more mitochondria to utilize fat as fuel

Fat Fuel The more trained a muscle, the greater its ability to use fat as fuel The more fatty acids released into the bloodstream, the more fat will be used by the muscle As exercise prolong, fat becomes the main fuel Not a major source of fuel for intense activity Requires more oxygen for aerobic breakdown (than glucose)

Protein--A Minor Source of Fuel Provides 2%-5% of energy needs during rest and low/moderate exercise Provides 10%-15% of energy needs during endurance exercise Most energy is from branched-chain amino acids Average diet provides ample amount of these amino acids -- supplements are not needed

Effects of Exercise Hypertrophy –Increase in cell size –Muscles enlarge as a result of repeated work Atrophy –Wasting away of tissues –Result of non-movement

Effects of Aerobic Exercise Increases red blood cell production to deliver oxygen Increases total blood volume Increases the number of capillaries in muscle tissue Strengthens the heart (muscle) Increases the number and size of mitochondria Increases muscle glycogen stores

VO 2 Max Measures the maximum oxygen that can be consumed per unit of time The more fit you are, the more oxygen you can consume (to do work) VO 2 max can be increased 15%-20% with training

Energy Needs For Athletes Estimate needs by monitoring weight and body fat Desirable body fat for male athletes: 5%- 15% Desirable body fat for female athletes: 12%-25% If weight falls, increase intake If body fat increases, cut back in fat (& kcal) and maintain activity

“Making Weight” The Wrong Way Lose weight so to qualify for a lower weight class Many will lose pounds by intense diuresis leading to dehydration Dehydration adversely affect performance Increases risk for decrease growth and development, abnormal psychological state, poor school performance, pulmonary problems, pancreatitis, kidney malfunction, heart problems, etc.

“Making Weight” The Right Way Gradual reduction in food intake long before competition Lower body fat composition If there is very little body fat to lose, athlete should consider competing in the higher weight class

Carbohydrates Main fuel for many types of activity Need to consume a diet moderate to high in CHO (~60% of total kcal) Adhere to the Food Guide Pyramid For aerobic and endurance activity, recommend 8-10 gm CHO/kg body weight Marathoners should consume ~ 600 gm of CHO/day

CHO Loading For events lasting longer than minutes Maximize glycogen stores Tapering of exercise while increasing CHO intake

CHO Loading Days Before Comp- etition Exercise Time rest CHO (grams)

Proteins Recommend gm protein/kg body weight The higher value for individuals participating in endurance exercise Needs are easily met by a normal diet Protein supplements are not necessary

Vitamins and Minerals Slightly higher needs for vitamin E and C (antioxidant properties) Thiamin, riboflavin, vitamin B-6, potassium, magnesium, iron, zinc, copper, and chromium needs may also be higher (role in metabolism or sweat) Extra vitamins and minerals needs are easily met by diet, especially by increasing intake of fruits and vegetables

Iron Needs Iron deficiency will affect performance Iron is loss in sweat, urine, gastrointestinal blood, and for the production of red blood cells “Foot-strike” destruction of iron and red blood cells by runners Women at risk because of menstruation Focus on iron-rich foods

Calcium Needs Restriction of dairy products by women Comprises bone health Amenorrhea and affect on bone density and osteoporosis Extra calcium does not compensate for amenorrhea Calcium deficiency can make it worst

Fluid Needs Average adult needs 1 ml/kcal of fluid per day Equivalent to 6-8 C per day Athletes need this and more Fluids are needed to maintain body’s cooling system Avoid losing more than 3% of body weight during exercise

Heat Exhaustion A depletion of blood volume from fluid loss by the body Body heat is lost primarily through evaporation of sweat Fluid loss through sweat is about 3-8 C per hour Humidity interferes with sweat production Decreases endurance, strength, performance Profuse sweating, headache, dizziness, nausea, weakness, visual disturbances

Heat Cramp Occurs in the skeletal muscle A complication of heat exhaustion Painful muscle contractions for 1-3 minutes at a time Ensure athletes have adequate salt and fluid intake Exercise moderately at first in the heat

Heat Stroke Internal body temperature reaches 105º F Symptoms: nausea, confusion, irritability, poor coordination, seizures, and coma Athletes should replace fluids and monitor weight change (fluid loss) Avoid exercising under hot, humid conditions

Hydration Thirst is not a reliable indicator of fluid needs General guideline: 2 C of fluids per each pound of weight loss during activity Drink fluid freely 24 hours before the event Drink 2 C two hours before the event Consume 1/2 - 1 C every 15 minutes for events lasting longer than 30 min. Goal is to lose no more than 3% of body weight

Sports Drink For Endurance Exercise Recommended for activity > 90 minutes in duration Sweat, CHO, and electrolytes lost in events <90 minutes are easily replaced by diet For events > 90 min. sports drink can help maintain blood glucose level and blood volume

Pre-Event Meal For endurance events Consumed 2-4 hours prior to event Consist primarily of CHO Low fat (<25% of energy intake) Little fiber (prevent bloating, gas) Moderate protein Avoid fatty, fried foods Use of glycemic index

Recovery Meal Consumed within 2 hours after endurance event CHO rich (1-2 g/kg body weight) to replace glycogen Repeat CHO meal over the next 2 hour interval Choose high glycemic index foods Aim for 3:1 CHO to protein ratio Fluids and electrolytes