During exercise our body uses different sources of energy, depending on availability and the request of the agency that can be used more quickly during muscle contraction is the creatine,
but it is available in very small quantity in our body and therefore sufficient only for the first few seconds of a sporting activity. This energy source is characterized, however, by a great immediacy of use and a large output power, even if for a very short time.
The carbohydrates are stored, in the form of glycogen and glucose, in the liver and muscles. Muscle glycogen is the second form of energy, but of short duration, and intervenes immediately after the creatine. Then we resort to glucose, which allows us a good supply of energy. The energy source is formed by the metabolism of adipose tissue, which is the major source of energy of the human being.
In special cases, such as in the presence of reduced supply and strong depletion of traditional energy stocks, the body also makes use of the proteins present in the muscles for energy.