Before discussing the contraction process itself, let us look first at how muscle fibers obtain the energy they need to contract. The direct source of energy for muscle contraction is ATP. ATP, however, is not stored in large amounts in muscle fibers and is depleted in a few seconds.
The secondary energy sources are creatine phosphate […]

The same basic metabolic systems are present in muscle as in other parts of the body. However, special quantitative measures of the activities of three metabolic systems are exceedingly important in understanding the limits of physical activity. These systems are (1) the phosphocreatine-creatine system, (2) the glycogenlactic acid system, and (3) the aerobic system.
Adenosine […]

In addition to the large usage of carbohydrates by the muscles during exercise, especially during the early stages of exercise, muscles use large amounts of fat for energy in the form of fatty acids and acetoacetic acid, and they use to a much less extent proteins in the form of amino acids. In fact, even […]

Phosphocreatine (also called creatine phosphate) is another chemical compound that has a high-energy phosphate bond, with the following formula:
Creatine ~ PO3-
This can decompose to creatine and phosphate ion, as shown to the left in Figure 84–1, and in doing so release large amounts of energy. In fact, the high-energy phosphate bond of phosphocreatine has more […]