Week 7 - Nutrients Physical Activity

Nutrients & Physical ActivityMilly Ryan-Harshman, PhD, RD Benefits of FitnessCompared with unfit people, physically fit people enjoy:More restful sleepImproved nutritional healthImproved body compositionImproved bone densityEnhanced resistance to infectious diseasesLower risk of some cancersLower risk of cardiovascular disease Benefits of FitnessLower risk of type 2 diabetesReduced risk of gallbladder disease (women)Lower incidence and severity of anxiety and depressionStronger self-imageLonger life and higher quality of life in the later years Benefits of Fitness Hill Climbing 101 Key Components of FitnessFlexibilityMuscle strengthMuscle enduranceCardiorespiratory endurance How Do My Muscles Gain Strength and Size?Muscle cells respond to an overload of physical activity by gaining strength and size, a response called hypertrophy. How Do My Muscles Gain Strength and Size? How Does Weight Training Benefit Health and Fitness?Weight training can emphasize either muscle strength or endurance.Muscle strength – combine high resistance (heavy weight) with a low number of repetitionsMuscle endurance – combine less resistance (lighter weight) with more repetitionsstyle.visibilitystyle.visibility How Does Cardiorespiratory Training Benefit the Heart?Cardiorespiratory endurance training enhances the ability of the heart and lungs to deliver oxygen to the muscles.The heart becomes stronger, breathing becomes more efficient, and the health of the entire body improves. How Does Cardiorespiratory Training Benefit the Heart?The accepted measure of a person’s cardiorespiratory fitness is maximal oxygen uptake (VO2 max). As the heart muscle becomes stronger, its cardiac output increases.The heart’s stroke volume also increases, i.e. the heart pumps more blood per beat.style.visibilitystyle.visibilitystyle.visibility The Active Body’s Use of FuelsPhysical activity is supported by different mixtures of glucose, fatty acids, and to a small extent amino acids, depending on the intensity and duration of its activities and depending on the body’s prior training. Glycogen/Glucose Use and Storage Anaerobic Use of GlucoseIntense activity uses glycogen quickly. Muscles must begin to rely on glucose which (unlike fat) can be partially broken down by anaerobic metabolism.Anaerobic breakdown of glucose yields energy to muscle tissue when energy demands outstrip the body’s ability to provide energy aerobically, but it does so by spending the muscle’s glycogen reserves. style.visibilitystyle.visibility Aerobic Use of GlucoseAerobic activity: Moderate physical activity, such as easy jogging, uses glycogen slowly.The person breathes easily and heart beats faster than at rest, but steadily.Muscles get energy from both glucose and fatty acids (this conserves glycogen stores). Balanced Fuel Consumption LactateLactate is produced by the anaerobic breakdown of glucose during intense activity.Lactate travels from muscles to liver where it is converted back to glucose.When rate of lactate production exceeds the rate of clearance, intense activity can be maintained for only one to three minutes. Activity Duration Affects Glucose UseGlucose use during physical activity depends on the duration of the activity and its intensity.First 10 minutes – glycogen used by musclesFirst 20 minutes of moderate activity – about 1/5 of available glycogen used upA person who exercises for longer than 20 minutes begins to use less glucose and more fat for fuelstyle.visibilitystyle.visibilitystyle.visibilitystyle.visibility Activity Duration Affects Glucose UseGlycogen depletion occurs after ~2 hours of vigorous exercise. After that, vigorous activity can continue for a short time as the liver converts lactate and some amino acids into glucose. Finally, hypoglycemia occurs which brings the nervous system almost to a halt, making intensive activity impossible.This is what marathon runners call “hitting the wall.”style.visibilitystyle.visibilitystyle.visibility Hitting the Wall Muscle metabolism and trainingMuscles are comprised of three main fiber types:    Type I   Slowly contracting red fibers where aerobic metabolism dominates.     Type IIA  Fibers of intermediate contractility where both anaerobic and aerobic processes are active.    Type IIB  Rapidly contracting white fibers where anaerobic metabolism is the major energy supply. Muscle FuelCreatine phosphateInitiator of muscle contraction & short burst activity Creatine phosphate and anaerobic glycolysis supply energy for intense, short work sessions while aerobic metabolism of both carbohydrates and fat supply energy for longer work sessions. Muscle FuelAerobic GlycolysisAnaerobic Glycolysis Muscle Fuel Muscle Fuel Maintaining Blood Glucose for ActivityFour strategies can help to maintain blood glucose to support sports performanceEat a high-carbohydrate diet (~70% of energy)Take glucose (usually in sports drinks) during activityEat carbohydrate-rich foods after performanceTrain the muscles to maximize glycogen storesstyle.visibilitystyle.visibilitystyle.visibilitystyle.visibility Glucose During ActivityGlucose ingested before and during endurance or intense intermittent activities (lasting more than 45 minutes) makes its way to the working muscles and adds to the glycogen stores.For activities less than 45 minutes, glucose probably won’t help (or harm) performance. Carbohydrate LoadingCarbohydrate loading is a technique to maximize muscle glycogen before a competition Can nearly double the muscle glycogen concentrationsCan benefit an athlete who keeps going 90 minutes or longer Carbohydrate Loading Glucose after ActivityEating high-carbohydrate foods within 2 hours after physical activity also enlarges glycogen stores. CrackersOrange juiceToastCerealSports drinks Degree of Training Affects Glycogen UseHighly trained muscles use less glucose and more fat than do untrained muscles to perform the same work, so their glycogen lasts longer. Using Protein and Amino Acids to Build Muscles and Fuel ActivityThe body handles protein differently during activity than during rest.In the hours after physical activity, muscles speed up the rate of protein synthesis.Physical activity, with a slight overload, calls into action protein-dismantling and protein-synthesis in individual muscle cells. Protein for Building Muscle TissuePhysical activity itself triggers the building of muscle proteins Protein for FuelProteins contributes about 10 percent of the total fuel used, both during activity and rest.Athletes use a little more protein as fuel than non athletes. Diet Affects Protein Use during ActivityA carbohydrate-rich diet spares protein from being used as a fuel.Some amino acids will be converted to glucose if your diet is low in carbohydrates. Intensity and Duration Affect Protein UseEndurance athletes who train for over an hour a day, engaging in aerobic activity of moderate intensity and long duration, may deplete their glycogen stores by the end of their training and become more dependent on body protein for energy.Anaerobic strength training does not use more protein for energy but does need more protein to build muscle. style.visibilitystyle.visibility Intensity and Duration Affect Protein UseThe protein needs of both endurance and strength athletes are higher than those of sedentary people, but not as high as the protein intakes many athletes consume. Degree of Training Affects Protein UseThe extent of training affects the use of protein.In strength athletes the higher the degree of training, the less protein a person uses during activity at a given intensity. How Much Protein Should an Athlete Consume? Iron and PerformancePhysically active young women are especially prone to iron deficiency because of:Habitually low intakes of iron-rich foodsHigh iron losses through menstruationHigh demands of muscles for iron Iron and PerformanceEarly in training, athletes may develop low blood hemoglobin.Sports anemia – an adaptive, temporary response to endurance training. Fluids and Temperature Regulation in Physical ActivityPhysically active people lose fluids and must replace them to avoid dehydration.A water loss of 7% is likely to lead to collapse. Temperature RegulationHeat stroke – a dangerous accumulation of body heat with a loss of fluid.SymptomsClumsiness Body temp above 104oFConfusion Nausea Dizziness HeadacheStumblingSudden cessation of sweating (hot, dry skin) Temperature RegulationHypothermia can occur in cold weather.Loss of body heat Fluid Needs during Physical ActivityEndurance athletes can lose 1.5 quarts or more of fluid during each hour of activity.During activity thirst becomes detectable only after fluid stores are depleted. Fluid Needs during Physical ActivityActive people need extra fluid, even in cold weather Water Water is the best drink for most physically active people, but endurance athletes need drinks that supply glucose as well as fluids. Electrolyte Losses and ReplacementThe body adapts to compensate for sweat losses of electrolytes. Athletes are advised to use foods, not supplements, to make up for these losses. Sodium DepletionHyponatremia – a dangerous condition of sodium depletionCan occur when endurance athletes drink such large amounts of water over the course of a long event that they overhydrate, diluting the body’s fluids to such an extent that the sodium concentration becomes too lowstyle.visibility Sodium DepletionTo prevent hyponatremia, sports drinks are more helpful than water.In the days before the event, athletes should not restrict salt in their diets. Other BeveragesCaffeine-containing drinks within limits may not impair performance, but water and fruit juice are preferred.Alcohol can impair performance in many ways and is not recommended. Food Feature: Choosing a Performance Diet Food Feature: Choosing a Performance Diet Controversy: Ergogenic Aids: Breakthroughs, Gimmicks, or Dangers?The large majority of legitimate research has not supported the claims made for ergogenic aids.Training serves an athlete better than any pills or powders. CaffeineCaffeine seems to provide a physical boost during endurance sports.Little or no effect for athletes in short-duration sports. CarnitineCarnitine is a nonessential nutrient often marketed as a “fat burner.”Carnitine supplementation neither raises muscle carnitine levels nor enhances exercise performance. Chromium PicolinateChromium picolinate promises to burn fat from the body.Chromium is an essential trace mineral involved in lipid and carbohydrate metabolism.Majority of studies showed no effect on body fatness, lean body mass, strength or fatigue.style.visibilitystyle.visibility CreatinePower athletes often use creatine supplements in the belief they enhance stores of the high-energy compound creatine phosphate in muscles.Creatine may enhance performance of high-intensity strength activities such as weight lifting or competitive swimming.But creatine does not benefit endurance activity.No long-term studies for safety.style.visibilitystyle.visibilitystyle.visibility Conjugated Linoleic AcidConjugated linoleic acid (CLA) arises from the essential fatty acid linoleic acid.In human beings, may provide a small increase in lean body mass and reductions in body fat, but no improvements in strength.Too early to know if CLA is worth the cost and is safe. Amino Acid SupplementsTo build protein, all the essential amino acids must be in the blood prior to physical work for maximum gains.The best source for these amino acids is food, not supplements.All amino acids are in a well-balanced diet.Supplements may not provide the ideal balance.Only a few grams of amino acids are needed and heavy doses from supplements are not needed. Supplements can lead to digestive disturbances.style.visibilitystyle.visibilitystyle.visibilitystyle.visibilitystyle.visibility Complete Meal ReplacersSpecialty drinks and candy bars, packed with vitamins, minerals, and other healthy-sounding goodies, appeal to athletes.They may taste good but fall short of providing “complete” nutrition and often are high in fat and sugar.These meal replacers may be useful as a pregame meal or a snack but are inferior to nutritious foods for meeting the high needs of athletes.style.visibilitystyle.visibilitystyle.visibility Hormone PreparationsAnabolic steroid hormones produce muscle size and strength far beyond that attainable by training alone, but are very dangerous. Hormone Preparations Steroid Alternative SupplementsSteroid alternatives, such as the officially banned “andro” (androstenedione) or DHEA, produce unpredictable results. Illegal to sell and banned by many sports organizations including the International Olympic Committee.These products may be as risky as steroid drugs and provide no competitive edge in sports. style.visibilitystyle.visibility