Sports Nutrition.pdf

Notes from Sept 6, 2024 Chapter 3 Skeletal Muscle Structure Sarcomeres are the smallest functional unit of muscle – contain thin (actin) and thick (myosin) filaments Contractile Unit The heads...

Notes from Sept 6, 2024 Chapter 3 Skeletal Muscle Structure Sarcomeres are the smallest functional unit of muscle – contain thin (actin) and thick (myosin) filaments Contractile Unit The heads of the myosin molecules form cross- bridges that bind reversibly to the actin filaments - brings Z-lines closer together. ATP is energy source that attaches at ATPase activity sites at the head of the myosin molecu Fiber Types Type I Fibers -Specialized for repeated contractions (relatively low forces) over prolonged period of time -High mitochondria count near high capillary supply -Relatively slow acting ATPases -Type 1 - Slow, oxidative Type Il fibers (Ila and lIx) -a shid, periordul contractions for -Fewer mitochondria and poorer capillary supply -Fast-acting ATPases Type lla - Fast, oxidative, glycolytic Type IIx - Fast, glycolytic Muscle Fiber Composition Muscles have a mixture of fiber types Elite marathoners may only have ~20% Type II in vastus lateralis while elite sprinters may have ~60% Type II in the same muscle Postural muscles tend to be composed predominantly of type I fibers (>70%) Example: soleus vs. gastrocnemius, deep core muscles Fiber type is genetically determined and is not pliable to any significant degree by training  ATP The energy source for muscle contraction is ATP, which is continuously regenerated during exercise from: phosphocreatine hydrolysis anaerobic metabolism of glycogen or glucose aerobic metabolism of acetyl-CoA - derived principally from breakdown of carbohydrate or fat. The carbon skeleton of some amino acids, called keto-acids, can be used as a fuel for oxidative metabolism but is not a major fuel for energy production during exercise (85% VO2max) Spirometry Closed-circuit spirometry Open and closed-circuit Closed-circuit is good for resting conditions but not exercise Oxygen is consumed causing the volume of the oxygen in the spirometer decreases and EE can be measured In open-circuit the subject breathes in ambient air and differences are found from exhaled and inhaled (Douglas Bag/ Breath- by-Breath) Computer analysis of Oxygen Consumption Breath-by-Breath Systems use computer analysis on a breath-by-breath basis of the Douglas Bag technique Give an accurate assessment of EE and register more frequent feedback of gas exchange Difficult to use anywhere but the lab so portable analyzers have been produced for free-living conditions Respiration chamber Measures energy balance because food intake can be accurately controlled Provides information about gas exchange (and therefore EE) Can calculate any energy losses in waste  Tracer Methods Doubly Labeled Water -Dose of two stable isotopes of water -Difference between the two excretion rates equals the carbon dioxide production rate -Expensive because of the availability of the tracer and must have a mass spectrometer to detect the tracer -Suitable for estimation of EE over days or weeks Labeled Bicarbonate -Any change in the body’s CO2 production results in the change in the percentage of labeled CO2 -Relatively inexpensive -Used for estimation of EE over hours up to a limited number of days Heart Rate Monitoring Linear relationship between HR and oxygen consumption during submaximal exercise can be used to estimate EE During rest slight movements or emotion can increase HR but not oxygen consumption Inexpensive but less accurate than other methods More accurate for group assessment of EE than individual Can be used in ‘free-living’ physical activities Accelerometer Registers the accelerations that the body makes The intensity and frequency of accelerations can help estimate activity level and therefore energy expenditure Provides a rough estimate but is useful in ‘free-living’ situations Tends to underestimate true energy expenditure Triaxial are better than uniaxial Activity Records Record activities during a 24-hour period Provides a rough estimation of energy expenditure Some people underestimate physical activity others may overestimate Uses a questionnaire that may not include all activities Overall average physical activity is reliable over a long-term period http://activitycalc.com/  Components of energy expenditure Resting metabolic rate -RMR is the largest component (60% to 75%) of the daily energy expenditure in relatively sedentary people Differences between persons primarily related to fat-free mass and influenced by age, gender, body comp, and genetic factors Diet-induced thermogenesis -The thermic effect of food represents about 10% of EE -Occurs as an result of digestion, absorption, metabolizing, and storage of food - EE may remain elevated for up to 8 hours Thermic effect of exercise -15% to 30% for exercise-related energy expenditure for sedentary persons -Most variable component of EE - exercise is voluntary -Can be much larger in active populations -As high as 80% in elite endurance athletes Energy balance between sports Intermittent sports such as tennis require relatively high energy outputs for short durations followed by a longer-period of low intensity The average EE is therefore relatively low Continuous sports such as cycling and running have relatively high EE >3000 kcal/day intake for elite females >4000 kcal/day intake for elite males Energy balance The energy balance is usually calculated over days or weeks and represents the difference between energy intake and energy expenditure When the energy intake exceeds the energy expenditure, a positive energy balance occurs, which will result in weight gain When energy intake is below energy expenditure, a negative energy balance occurs, and weight loss will result  Energy balance extremes Lower limits of energy expenditure Female gymnasts, ballet dancers, and ice dancers often have daily energy intakes between 1,000 kcal and 2,000 kcal In some cases this intake is only 1.2 to 1.4 times the resting metabolic rate, which can result in nutritional deficiency Upper limits of energy expenditure Cycling, triathlon, and ultraendurance running are sports that may require energy expenditures as high as 8,600+ kcal/day Considerations for Energy Intake (Tour de France) For long endurance races intake during the competition is difficult and voluminous eating must be done afterward Note: hunger feelings may be depressed for several hours GI problems make absorbing the necessary large quantities difficult especially in the last week Weight, and therefore energy balance, is typically maintained by the Tour de France athletes Carbohydrate in a drink solution during the competition or training can also help maintain energy balance More Upper Limits of Energy Expenditure Norwegian cross country skiers: 8,600 kcal/day Ultraendurance runner case study: 10,750 kcal/day For the above two cases energy intake was high and accounted for EE resulting in no weight loss Robert Scott (1911-12) and Ernest Shackleton (1914-16) man-hauled sleds for 10 hours a day for ~160 consecutive days Total EE over the whole expedition was ~1,000,000 kcal Energy intake was limited and weight loss occurred