Creatine is a protein molecule that is stored in muscle.
For activities lasting 10 seconds or less, ATP is the energy source for the muscle. It has been shown that muscular fatigue is related to phosphocreatine depletion in muscle, and that creatine supplementation can enhance the levels of both creatine and phosphocreatine in skeletal muscle. Normal requirements for creatine are in the range of two grams per day. The body produces about one gram of creatine in the liver each day, and most American diets, which include meats, provide at least one additional gram of creatine daily. This two gram amount of liver produced and diet consumed creatine is more than adequate for participation in all high school sports.