Phosphocreatine (Phosphagen) System

Anaerobic metabolic processes supply ATP from phosphocreatine (PCr) and glycolysis without oxygen. The in-muscle concentration of preformed ATP is 25 to 33 percent of the concentration of PCr. The enzyme creatine kinase can break apart PCr into inorganic phosphate and creatine, with a resultant release of energy. The free inorganic phosphate is united with ADP to reform ATP. The breakdown of PCr is not reversible until energy is obtained from other sources (mainly through oxidative metabolic processes). The volume of energy that can be supplied by the breakdown of PCr is vast, and it can be produced instantaneously. However, the length of time that this high volume of energy can be supplied is never greater than 10 seconds because of the limited amount of PCr stored in tissue. The formation of energy from PCr breakdown is directly linked to the intensity of exercise: The higher the exercise intensity, the greater the reliance on PCr breakdown as a source of energy. Athletes performing maximal exercise for 8 to 10 seconds (sprint, vault, jumps) must take a break of 2 to 4 minutes to allow for the regeneration of PCr before undertaking another maximal bout of exercise.

Creatine monohydrate supplementation is popular because athletes want to increase the storage of PCr, with the hope of increasing both capacity and power.