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Energy Requirements of Skeletal Muscles Metabolism of skeletal muscle depends on O2 uptake -- depends on whether exercise is light, moderate, heavy, which depends on a person’s maximum capacity for aerobic exercise --Maximal oxygen uptake (aerobic capacity), abbreviated VO2 max It is expressed as ml O2/min/kg of body weight High = 84 ml/min/kg (young male athlete) Low = 12 ml/min/kg (older, sedentary people) Capacities for Aerobic Oxygen From the Internet Muscle Fuel Consumption During Exercise Light – (and resting muscles) get most of their energy from fatty acids Moderate (just below the lactate threshold) energy is obtained about equally from fatty acids and glucose Heavy – glucose, (from the muscle’s stored glycogen and from blood plasma) becomes increasingly important LEG Muscle GLUCOSE Consumption During Exercise GLUCOSE UPTAKE: Exercise stimulates glut 4 transporters to be inserted into the plasma membrane of muscle cells. The more intense the exercise, the more glut4 transporters are inserted. -- this is independent of insulin CYCLE ERGOMETER Oxygen Debt: the length of time it takes to ‘catch your breath’ after lactic acid build-up Oxygen debt is the amount of oxygen that you owe yourself to convert lactate back into pyruvate and restore aerobic respiration. • Click here for a 1 minute video Production of Phosphocreatine Rapid production of ATP is accomplished by combining ADP with inorganic phosphate derived from phosphocreatine Phosphocreatine is a high-energy reserve found in muscle cells. The reverse reaction is catalyzed during rest (to restore depleted supplies. Different Exercise Regimens between twins This is a famous photograph showing differences in body types between identical twins that simply used different exercise regimens. Skinny guy – a runner, high aerobic capacity and endurance Buffed guy – a weight lifter, does his exercise with short bursts of energy, rather than endurance. What’s going on here? SLOW- AND FAST-TWITCH FIBERS SLOW-TWITCH: Contract slowly often “postural” high oxidative capacity contract without fatigue numerous mitochondria myoglobin sometimes called red fibers FAST-TWITCH: Contract quickly less capillary supply fewer mitochondria adapted to metabolize anaerobically use a glycogen storage examples: soleus (leg) examples: extraocular muscles that position the eyes Relative Abundance of Fiber Types Muscle fatigue • Defined as a reversible, exercise-induced reduction in the ability of a muscle to generate force • Many causes, which seem to be determined by the type of exercise. • E.g. lifting an extremely heavy weight. K+ builds up outside of muscle cells Adaptation to Endurance Exercise Training Student activity: Compare the storage of fatty acids in obese people with the storage of fatty acids in athletes. What’s the difference?