muscle metabolism


muscle metabolism

The consumption of energy by all cells, including those of muscle tissue, to perform work. The source of chemical energy, adenosine triphosphate (ATP), is metabolized to adenosine diphosphate (ADP). If the energy requirement is short-term, the ADP is converted back to ATP. This process is too slow to keep up with energy demands during long-term exercise; thus, consumption of other fuels is required. The main sources of fuel for muscles are carbohydrates and lipids. Before being available for intracellular metabolism, glycogen is obtained when glucose is converted to glycogen. The main lipid fuel is free fatty acids present in plasma. Carbohydrates can be metabolized either in the presence of oxygen (aerobically) or in its absence (anaerobically), but lipids can be metabolized only aerobically. During light exercise or when the body is at rest, muscle metabolism is usually entirely aerobic, and the source of fuel is the free fatty acids in plasma. During intense exercise, metabolism of the fatty acids cannot keep up with the demand, and glycogen is used for energy. However, as intense exercise continues, glycogen stores are exhausted, and free fatty acids become the principal source of energy. Trained athletes have an increased ability to metabolize fatty acids as compared with sedentary people; this permits athletes to exercise longer and at higher work rates than untrained people. Athletic trainers have found that muscle glycogen stores can be increased by carbohydrate loading. Working articulation.See also: metabolism