During high intensity exercise, the demand in working muscles for ATP increases several hundredfold as compared to muscles at rest. Creatine phosphate acts as the primary resupplier of ATP levels for high intensity efforts lasting up to and around 25 seconds. Due to the important role creatine plays in recharging ATP levels, researchers and athletes are focusing on how they can raise levels of creatine in the body. Neither creatine phosphate nor ATP can be directly supplemented in the diet. Creatine phosphate levels will increase, however, with a rise in total creatine levels.
Creatine is manufactured in the body by arginine, glycine and methionine.
In the diet it is found in meat, especially red meat, and also in small amounts from plants. A clinical study of 17 subjects demonstrated that creatine monohydrate supplementation increased the total creatine pool in muscle. The subjects were administered 5 g of creatine monohydrate four or six times a day for 2 or more days. Supplementation resulted in a significant increase in the total creatine content of the quadriceps femoris muscle. It has been theorized that a limited supply of ATP is one of the major limiting factors in maintaining peak muscle performance.