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) 0-90 min anaerobic b/c the body requires

Capacities for Aerobic Oxygen 0-90 min anaerobic b/c the body requires

Muscle Fuel Consumption During Exercise Light – (and resting muscles) get most of their energy from fatty acids Moderate (just below lactate threshold) energy obtained about equally from fatty acids and glucose Heavy – glucose, (from glycogen) becomes increasingly important

LEG Muscle GLUCOSE Consumption During Exercise CYCLE ERGOMETER Exercise stimulates glut 4 transporter insertion into plasma membrane of muscle cells. More intense the exercise = more glut4 transporters. -- independent of insulin

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.

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 Photo shows 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 examples: soleus (leg) FAST-TWITCH: Contract quickly less capillary supply fewer mitochondria adapted to metabolize anaerobically use a glycogen storage 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?