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© 2006 Thomson-Wadsworth Nutrition and physical activity are interactive ◦ Each influences the other ◦ Demands all three energy-yielding nutrients Physical activity benefits the body’s nutrition by helping to regulate the use of fuels ◦ Pushing toward lean body composition ◦ Increasing the daily caloric allowance With more calories come more nutrients Improvement is not only possible but an inevitable consequence of becoming more active ◦ As you improve your physical fitness, you not only feel better and stronger, but you look better ◦ Physically fit people walk with confidence and purpose Posture and self-image improve along with physical fitness Training ◦ Regular practice of an activity ◦ Physical adaptations of the body with improvement in Flexibility, strength, or endurance Fitness depends on ◦ Physical activity Bodily movement produced by muscle contractions that substantially increase energy expenditure ◦ Exercise Planned, structured, and repetitive bodily movement that promotes or maintains physical fitness ◦ More restful sleep During rest, the body repairs injuries, disposes of wastes, and builds new physical structures ◦ Better nutritional health Physical activity expends energy and thus allows people to eat more food Active people can consume more nutrients and be less likely to develop nutrient deficiencies ◦ Enhanced resistance to colds and infections ◦ Stronger circulation and lung function ◦ Improved body composition A balanced program of physical activity limits body fat and increases or maintains lean tissue ◦ Improves bone density Weight-bearing physical activity builds bone strength and protects against osteoporosis ◦ Lower risk of some kinds of cancer Lifelong physical activity may help to protect against colon cancer, breast cancer, and some other cancers ◦ Lower risks of cardiovascular disease Physical activity lowers BP, slows resting pulse rate, lowers total cholesterol, and raises HDL cholesterol Some research suggests that physical activity may also be of benefit by reducing intra-abdominal fat stores ◦ Lower risks of type 2 diabetes Physical activity normalizes glucose tolerance Regular physical activity reduces the risk of developing type 2 diabetes and benefits those who already have the condition ◦ Reduced risk of gallbladder disease (women) ◦ Lower incidence and severity of anxiety and depression ◦ Stronger self-image ◦ Longer life and higher quality of life The American College of Sports medicine (ACSM) and the Dietary Guidelines for Americans, 2005 ◦ Specify that people need to spend an accumulated minimum of 30 minutes in some sort of physical activity on most days of each week ◦ The DRI committee recommends at least 60 minutes of moderately intense activity Flexibility ◦ The capacity of the joints to move through a full range of motion ◦ The ability to bend and recover without injury Muscle strength ◦ The ability of muscles to work against resistance Muscle endurance ◦ The ability of a muscle to contact repeatedly within a given time without becoming exhausted Cardiorespiratory endurance ◦ The ability to perform large-muscle dynamic exercise of moderate-to-high intensity for prolonged periods A person who practices physical activity adapts by becoming better able to perform it after each session ◦ With more flexibility, more strength, and more endurance © 2006 Thomson-Wadsworth How Do My Muscles become Physically Fit? ◦ Overload An extra physical demand placed on the body An increase in the frequency, duration, or intensity ◦ Hypertrophy An increase in size in response to use Muscle cells and tissues respond to an overload of physical activity by gaining strength and size ◦ If not called on to perform, muscle cells dwindle and weaken; they atrophy How Does Weight Training Benefit Health and Fitness? ◦ Weight training/ Resistance Training The use of free weights or weight machines to provide resistance for developing muscle strength and endurance A person’s own body weight may also be used to provide resistance as when a person does push-ups, pull-ups, or sit-ups Helps to prevent and manage several chronic diseases and enhances psychological well-being Weight training promotes strong muscles in the back and abdomen (less back injury) Helps prevent the decline in physical mobility that often accompanies aging Older adults gain muscle strength Improve muscle endurance ◦ Enables them to walk significantly longer before exhaustion Can help to maximize & maintain bone mass ◦ Even in women past menopause, a one-year program of weight training improves bone density ◦ The more weight lifted, the greater the improvement Can emphasize either muscle strength of muscle endurance ◦ To emphasize muscle strength Combine high resistance with a low number of repetitions ◦ To emphasize muscle endurance Combine less resistance with more repetitions Enhances performance in other sports ◦ Swimmers can develop a more efficient stroke ◦ Tennis players can develop a more powerful serve How Does Cardiorespiratory Training Benefit the Heart? ◦ Blood HDL increases ◦ Effective activities elevate the heart rate, are sustained for longer than 20 minutes, and use more of the large-muscle groups of the body ◦ Pulse rate falls ◦ The muscles that inflate and deflate the lungs gain in strength and endurance Breathing becomes more efficient ◦ Blood moves easily through the blood vessels Fuels that support body activity are ◦ Glucose From carbohydrate ◦ Fatty acids From fat ◦ To a small extent, amino acids From protein ◦ The body uses different mixtures of fuels depending on the intensity and duration of its activities and depending on its own prior training During rest ◦ Little more than half of energy from fatty acids Most of the rest from glucose A little from amino acids During physical activity ◦ The body adjusts its fuel mix to use the stored glucose of muscle glycogen ◦ In the early minutes of activity, glycogen provides the majority of energy the muscles use to go into action As the activity continues, messenger molecules, including epinephrine, flow into the bloodstream to signal the liver and fat cells to liberate their stored nutrients Primarily glucose and fatty acids As activity continues ◦ Glucose from the liver’s stored glycogen and dietary glucose absorbed from the digestive tract also become important sources of fuel for muscle activity The body constantly uses and replenishes its glycogen ◦ The more carbohydrate a person eats The more glycogen muscles store (up to a point) The longer the stores will last to support physical activity A classic report compared fuel use during activity by three groups of runners, each on a different diet ◦ The high-carbohydrate diet enables the athletes to work longer before exhaustion The body’s glycogen stores are much more limited than its fat stores ◦ Glycogen can easily support everyday activities but is limited to less than 2,000 calories of energy How long a person’s glycogen will last while exercising depends on both diet and intensity of the activity ◦ Fat stores can usually provide more than 70,000 calories and fuel hours of activity without running out Not requiring oxygen Requires strength but does not work the heart & lungs Intense activity uses glycogen quickly ◦ Muscles must begin to rely more heavily on glucose Which can be partially broken down by anaerobic metabolism Anaerobic Use of Glucose ◦ Glucose can yield energy quickly ◦ Anaerobic breakdown of glycogen yields energy to muscle tissue when energy demands outstrip the body’s ability to provide energy aerobically Lavish spending of the muscles’ glycogen stores Lactic acid ◦ A compound produced during the breakdown of glucose during anaerobic metabolism During intense activity, anaerobic breakdown of glucose produces lactic acid ◦ When production of lactic acid exceeds the ability of muscles to use it, they release it, and it travels in the blood to the liver Liver enzymes convert the lactic acid back into glucose Glucose can then return to the muscles to fuel additional activity Moderate physical activity uses glycogen slowly ◦ The individual breathes easily and the heart beats at a faster pace than at rest but steadily ◦ The activity is aerobic During aerobic metabolism muscles extract their energy from both glucose and fatty acids ◦ By depending partly on fatty acids, moderate activity conserves glycogen stores At low intensities, lactic acid is readily cleared from the blood by the liver At higher intensities, lactic acid accumulates When the rate of lactic acid production exceeds the rate of clearance, intense activity can be maintained for only one to three minutes Lactic acid was long blamed for a type of muscle fatigue ◦ Evidence disputes this idea ◦ Muscles produce lactic acid during a type of fatigue ◦ But the lactic acid does not cause the fatigue Glucose use during physical activity depends on the duration of the activity ◦ As well as on its intensity In the first 10 minutes or so of activity ◦ The active muscles rely almost entirely on their own stores of glycogen Within the first 20 minutes or so of moderate activity ◦ A person uses up about one-fifth of the available glycogen As the muscles devour their own glycogen, they increase their uptake of blood glucose dramatically ◦ During moderate activity, blood glucose declines slightly Reflecting its use by the muscles A person who exercises moderately for longer than 20 minutes begins to use less glucose and more fat for fuel ◦ Still, glucose use continues If the activity goes on long enough and at a high enough intensity, muscle and liver glycogen stores will run out almost completely Glycogen depletion generally occurs after about two hours of vigorous exercise ◦ Physical activity can occur for a short time thereafter only because the liver produces some glucose from available lactic acid and certain amino acids This minimum amount of glucose may briefly forestall exhaustion But when hypoglycemia accompanies glycogen depletion, it brings nervous system function almost to a halt Maintaining Blood Glucose for Activity ◦ Eat a high-carbohydrate diet regularly ◦ Take glucose (usually in sports drinks) periodically during endurance activities ◦ Eat carbohydrate-rich foods after performance ◦ Train the muscles to maximize glycogen stores Carbohydrate loading Glucose During Activity ◦ Glucose ingested before and during exhausting endurance activities makes its way from the digestive tract to the working muscles Augmenting dwindling internal glucose supplies from the muscle and liver glycogen stores Especially during games which last for hours and demand repeated bursts of intense activity, athletes benefit from carbohydrate-containing drinks taken during the activity Before concluding that sugar might be good for your own performance, consider first whether you engage in endurance activity ◦ Do you run, swim, bike, or ski nonstop at a rapid pace for more than 45 minutes at a time, or do you compete in games lasting for hours? ◦ If not, the sugar picture changes For an everyday activity lasting less than 60 minutes, sugar probably won’t help (or harm) performance Even in athletes, extra carbohydrate does not benefit those who engage in sports in which fatigue is unrelated to blood glucose ◦ ◦ ◦ ◦ 100-meter sprinting Baseball Casual basketball Weight lifting Carbohydrate Loading ◦ A regimen of moderate exercise, followed by eating a high-carbohydrate diet ◦ Glycogen stored beyond their normal capacity Can nearly double muscle glycogen concentration Carbohydrate Loading ◦ Glycogen storage occurs slowly in the plan presented in Table 10-2 ◦ Athletes must alter their training in the days just before the event Quick method of carbohydrate loading that has produced promising preliminary results • Eat a high-carbohydrate diet after a short but very intense bout of exercise Can benefit an athlete who must keep going for 90 minutes or longer Shorter durations- a regular high-carb diet In a hot climate, extra glycogen confers an additional advantage • As glycogen breaks down, it releases water • Which helps to meet the athlete’s fluid needs Glucose After Activity ◦ Eating high-carbohydrate foods after physical activity also enlarges glycogen stores Train normally, and then, within 2 hours after physical activity, consume a high-carbohydrate meal This method accelerates the rate of glycogen storage by 300% for a while This is especially important to athletes who train hard more than one time a day For athletes who don’t feel like eating right after exercise, high-carbohydrate energy drinks are available ◦ Fruit-flavored commercial beverages used to restore muscle glycogen after exercise or as a pregame beverage For athletes wishing to maximize muscle glycogen synthesis after strenuous training, eating foods with a high glycemic index may restore muscle glycogen most rapidly Muscles that deplete their glycogen stores through work adapt to store greater amounts of glycogen to support that work Trained muscles burn more fat, and at higher intensities, than untrained muscles ◦ So they require less glucose to perform the same amount of work People with diabetes ◦ Who must take insulin or insulin-eliciting drugs Sometimes find that as their muscles adapt to physical activity, they ca reduce their daily drug dose ◦ Physical activity may also improve type 2 diabetes by helping the body lose excess fat Factors that affect glucose use during physical activity ◦ Carbohydrate intake ◦ Intensity and duration of the activity ◦ Degree of training When endurance athletes “fat load” by consuming high-fat, low-carbohydrate diets for one to three days… ◦ Performance is impaired because their small glycogen stores are depleted quickly Endurance athletes who adhere to a high-fat, low-carbohydrate diet for more than a week… ◦ Adapt by relying more on fat to fuel activity ◦ Even with fat adaptation performance benefits have not been consistently shown High-fat diets carry risks of heart disease Fat restriction is not recommended either ◦ <20% of total energy intake may fail to consume adequate energy and nutrients ◦ Consume 20%-30% of their energy from fat As fuel for activity, body fat stores are more important than fat in the diet ◦ Fat stores can fuel hours of activity ◦ Body fat is (theoretically) an unlimited source of energy Even the lean bodies of runners carry enough fat to fuel several marathons Early in activity, muscles begin to draw on fatty acids from two sources ◦ Fats stored within the working muscles ◦ Fats from fat deposits such as fat under the skin Intensity and Duration Affect Fat Use ◦ The intensity of physical activity affects the percentage of energy contributed by fat Fat can be broken down for energy only by aerobic metabolism When the intensity of activity becomes so great that energy demands surpass the ability to provide energy aerobically, the body cannot burn more fat Instead, it burns more glucose ◦ The duration of activity matters to fat use At the start of activity, the blood fatty acid concentration falls After about 20 minutes of activity, the blood fatty acid concentration rises above normal resting concentrations Degree of Training Affects Fat Use ◦ Training stimulates muscles to develop more fatburning enzymes Aerobically trained muscles burn fat more readily than untrained muscles With aerobic training, the heart and lungs become stronger and better able to deliver oxygen to the muscles during high-intensity activities This improved oxygen supply enables the muscles to burn more fat Intense, prolonged activity may increase your basal metabolic rate (BMR) Athletes in training, whether endurance athletes or power athletes, expend huge amounts of energy each day while practicing ◦ The harder an athlete works, the more energy the athlete spends ◦ The greater the intensity and the longer the duration of the activity, the longer the metabolic rate remains elevated ◦ The more muscle is developed the more metabolically active Protein for Building Muscle Tissue ◦ In the hours of rest that follow physical activity Muscles speed up their rate of protein synthesis They build more of the proteins they need to perform the activity Eating protein, together with carbohydrate, enhances protein synthesis Dietary protein provides the needed amino acids for the synthesis of new muscle protein Protein for Fuel Protein contributes about 10% of the total fuel used Both during activity and during rest Diet Affects Protein Use during Activity A carbohydrate-rich diet spares protein from being used as fuel Some amino acids can be converted into glucose when needed If your diet is low in carbohydrate, much more protein will be used in place of glucose Intensity and Duration Affect Protein Use ◦ Endurance athletes may deplete glycogen and use protein for energy Anaerobic strength training does not use more protein for energy ◦ Does demand more protein to build muscles The 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 Use ◦ Particularly in strength athletes, the higher the degree of training, the less protein a person uses during an activity at a given intensity Most athletes need more protein than do sedentary people ◦ Average protein intakes in the U.S. are high enough to cover those needs ◦ Athletes in training should attend to protein needs but should back up the protein with ample carbohydrate Otherwise, they will burn off as fuel the very protein they wish to retain as muscle The DRI committee does not recommend high protein intakes for athletes ADA & Dietitians of Canada recommend protein intakes slightly more than 0.8 g/kg of body weight Athletes who eat a balanced, highcarbohydrate diet consume enough protein ◦ No special foods, protein shakes, or supplements Many vitamins and minerals assist in releasing energy from fuels and transporting oxygen © 2006 Thomson-Wadsworth Vitamin C is needed for the formation of the protein collagen ◦ The foundation material of bones and the cartilage that forms the linings of joints and other connective tissues Folate and vitamin B12 help build red blood cells Calcium and magnesium help make muscles contract © 2006 Thomson-Wadsworth In general, people who eat well-balanced meals do not need vitamin or mineral supplements ◦ Vitamin E and iron do merit special attention Vitamin E is addressed because so many athletes take supplements of it Iron is discussed because some female athletes may be unaware that they need supplements Vitamin E is a potent fat-soluble antioxidant ◦ Defends cells membranes against oxidative damage Some athletes take megadoses of vitamin E in hopes of preventing such oxidative damage to muscles ◦ Supplementation with vitamin E does seem to protect against exercise-induced oxidative stress, ◦ There is little evidence that vitamin E supplements can improve performance Physically active young women, especially those who engage in endurance activities, are prone to iron deficiency Iron losses in sweat may contribute to deficiency The muscles’ high demands for iron to make the ironcontaining molecules of aerobic respiration Habitually low intakes of iron-rich foods, high iron losses through menstruation, and extra demands can contribute to iron deficiency in young female athletes Vegetarian female athletes are particularly vulnerable to iron insufficiency ◦ The bioavailability of iron is often poor in plant-based diets ◦ Vegetarian female athletes ◦ Vegetarian diets are usually rich in vitamin C ◦ To protect against iron deficiency, vegetarian athletes need to pay close attention to their intake of good dietary sources of iron (fortified cereals, legumes, nuts, and seeds) And include vitamin C-rich foods with each meal As long as vegetarian athletes, like all athletes, consume enough nutrient-dense foods, they can perform as well as anyone The body’s need for water far surpasses its need for any other nutrient ◦ If the body loses too much water, its life-supporting chemistry is compromised The exercising body loses water primarily via sweat Second to that, breathing costs water, exhaled as vapor During physical activity, both routes can be significant ◦ Dehydration is a real threat The first symptom is fatigue A water loss of even 1%-2% of body weight can reduce a person’s capacity to do muscular work A person with a water loss of ≈7% is likely to collapse Even in cold weather, the body still sweats and needs fluids ◦ The fluids should be warm or at room temperature to help prevent hypothermia © 2006 Thomson-Wadsworth Endurance athletes can lose 2 or more quarts of fluid in every hour of activity ◦ The digestive system can only absorb about a quart or so an hour The athlete must hydrate before and rehydrate during and after activity to replace all the lost fluid ◦ In hot weather, the digestive tract ay not be able to absorb enough water fast enough to keep up with an athlete’s sweat losses Some degree of dehydration becomes inevitable © 2006 Thomson-Wadsworth Athletes who rely on thirst to govern fluid intake can easily become dehydrated ◦ During activity thirst becomes detectable only after fluid stores are depleted ◦ Don’t wait to feel thirsty before drinking © 2006 Thomson-Wadsworth Endurance athletes are an exception ◦ They need more from their fluids than water alone ◦ The first priority for endurance athletes should always be replacement of fluids To prevent life-threatening heat stroke ◦ Endurance athletes need carbohydrate to supplement their limited glycogen stores During physical activity, the body loses electrolytes in sweat ◦ The minerals sodium, potassium, and chloride The body’s adaptation to physical activity includes better conservation of these electrolytes © 2006 Thomson-Wadsworth Many different diets can support an athlete’s performance ◦ Food choices must obey the rules of diet planning Nutrient Density ◦ Athletes need a diet composed mostly of nutrientdense foods That supply a maximum of vitamin and minerals for the energy they provide ◦ When athletes eat mostly refined, processed foods that have suffered nutrient losses and contain added sugar and fat, their nutrition status suffers © 2006 Thomson-Wadsworth Balance ◦ Athletes must eat for energy Their energy needs can be immense ◦ Athletes need full glycogen stores Need to strive to prevent heart disease and cancer by limiting fat especially saturated fat A diet that is high in carbohydrate (60%-70% of total calories), moderate in fat (20%-39%), and adequate in protein (10%-20%) is best for all these purposes © 2006 Thomson-Wadsworth © 2006 Thomson-Wadsworth © 2006 Thomson-Wadsworth Ergogenic Aids ◦ Appeal to performance-conscious people Protein powders Amino acid supplements Caffeine pills Steroid replacers “muscle builders” Vitamins and more ◦ Research findings do not support the claims ◦ Almost anything can be sold under the label of “dietary supplement” with scant regulation by authorities © 2006 Thomson-Wadsworth Amino Acid Supplements ◦ Are unnecessary ◦ Healthy athletes eating a well-balanced diet never need them ◦ In a few cases these supplements have proved dangerous Amino acids complete for carriers An overdose of one can limit the availability of some other needed amino acid Can lead to digestive disturbances and excess water accumulation in the digestive tract © 2006 Thomson-Wadsworth Branched-chain amino acids (BCAA) ◦ Advertised as a source of fuel for the exercising body ◦ Compared to glucose and fatty acids, provide very little fuel to working muscles When they are needed, trained muscles have plenty on hand ◦ No consistent findings exist to indicate a performance benefit from supplemental BCAA ◦ A diet too low in carbohydrates or energy triggers activity of an enzyme that breaks down BCAA for energy An athlete who consumes adequate carbohydrate and calories conserves BCAA in the tissues ◦ Large doses of BCAA can raise plasma ammonia concentrations, causing fatigue © 2006 Thomson-Wadsworth ◦ Provides mental stimulation ◦ Provides a physical boost during endurance sports Athletes performing high-intensity, short-duration activities derive little or no performance edge Adverse effects ◦ Upset stomach, nervousness, irritability, headaches, dehydration, and diarrhea, diuretic ◦ High doses constrict the arteries and raise blood pressure above normal Making the heart work harder to pump blood An effect potentially detrimental to sports performance Some competitions prohibit >5-6c of coffee in a two-hour period prior to competition ◦ Athletes are disqualified if urine tests detect more than this amount Often marketed as a “fat burner’ In the body, does help to transfer fatty acids across the membrane that encases the cell’s mitochondria In studies, carnitine supplementation for 7 to 14 days did not influenced fat or carbohydrate oxidation Nor do such supplements enhance exercise performance For those concerned about adequate carnitine ◦ Milk and meat products are good sources ◦ Carnitine is nonessential The body makes plenty for itself when needed ◦ Essential trace mineral involved in carbohydrate and lipid metabolism ◦ Studies show no effects of chromium picolinate on body fatness, lean body mass, strength, or fatigue Chromium picolinate safety ◦ Allergic reactions ◦ The release of chromium from chromium picolinate creates molecular free radicals that can contribute to potentially harmful levels of oxidative stress in body tissues Creatine ◦ The outcomes of some studies suggest that creatine supplementation may enhance performance of highintensity strength activity such as weight lifting or repeated sprinting ◦ Other studies have found no effect of creatine supplements on strength performance Creatine safety ◦ Appropriate long-term studies are lacking ◦ Cramping and gastrointestinal distress seem to occur with about the same dosages reported to benefit performance ◦ Short-term supplementation may pose risk to athletes with kidney disease or other conditions © 2006 Thomson-Wadsworth ◦ Medical and fitness experts voice concern that creatine is being taken in huge doses and that children as young as 9 years old are taking it with unknown consequences ◦ Creatine levels from foods, even diets high in creatine-rich foods like red meat, do not approach the amount athletes take in supplement form © 2006 Thomson-Wadsworth Protein Powders ◦ Whey protein Can supply amino acids to the body Offers no special benefits beyond those provided by ordinary milk or yogurt Extra protein will not stimulate muscle growth ◦ Muscle growth is stimulated by physical activity ◦ Not by excess protein Purified protein contains none of the other nutrients needed to support the building muscle ◦ An entire array of nutrients from food is required © 2006 Thomson-Wadsworth ◦ The testes and adrenal glands in men and the adrenal glands in women make anabolic steroid hormones naturally ◦ Often taken without any medical supervision or testing ◦ Synthetic versions of these natural hormones produce accelerated muscle bulking in response to physical activity in both men and women Injections of these “fake” hormones produce muscle size and strength far beyond that attainable by training alone At the price of great risks to health “steroid rage” Steroid Alternative Supplements ◦ “andro” (androstenedione) or DHEA or a number of herbal preparations Claims made for these substances - that they reduce fat, build muscle, slow aging, and other miracles - are unsupported by research These substances are converted to active hormones by body tissues Users incur many of the same serious risks as for steroid drugs People respond unpredictably © 2006 Thomson-Wadsworth Herbal or even insect sterols hawked as “natural” substitutes for steroid drugs are useless in sports ◦ The body cannot convert them into human steroids Nor do they stimulate the body’s own steroid production ◦ These products may contain toxins “natural” does not mean “harmless” © 2006 Thomson-Wadsworth Human Growth Hormone (HGH) Athletes in power sports are most likely to experiment with HGH ◦ Can induce huge body size ◦ Is less readily detected in drug tests than steroids ◦ Believing the injectable hormone will provide the benefits of anabolic steroids without the dangerous side effects ◦ Alternatively, they may take growth hormone “stimulators” such as the amino acids ornithine and arginine ◦ HGH causes the disease acromegaly ◦ The amino acids ornithine and arginine do not stimulate growth hormone release © 2006 Thomson-Wadsworth