D uring high-intensity, short duration exercise, the amount of energy supplied is determined by the amount of phosphocreatine stored in the skeletal muscle. As phosphocreatine stores become depleted, fatigue will ultimately occur, reflecting an inability to resynthesize ATP, the primary fuel for muscle, at the rate required. Therefore, it has been presumed that increasing muscle creatine content may increase the availability of phosphocreatine and allow for a quicker rate of resynthesis of ATP during and following brief, high-intensity exercises. A dditional creatine is supplied to the body through protein-rich sources, particularly beef, pork, herring, tuna, and salmon. Generally, a mixed diet provides about one gram of creatine each day.
Creatine supplements are yet another form of acquiring creatine.
This pill form is preferred by many supplement users because of the high fat content of most food sources. In order to receive the 20 g of creatine recommended as a loading dose by manufacturers, one would have to consume 10 pounds of raw steak. However, the increase in body weight can not be attributed exclusively to creatine supplementation. T he muscle cell creatine saturation effect occurs after five days of loading on 20 g of creatine. Once the muscle cell is overloaded with creatine, it is easily maintained at this level with about two 5-g doses a day.