Creatine is an amino acid made by your liver, pancreas and kidney. Creatine is also available in dietary sources like fish and meat. In addition, it can be synthesized in the laboratory, although its efficacy as a supplement remains controversial. Your muscles store creatine as creatine phosphate, a source of ATP, which provides energy.
History
Creatine was first identified in 1832 in meat. In the 1970s Soviet scientists claimed that oral supplements of creatine could boost the performance of athletes in brief, intense events. Since then, the use of creatine supplements has grown among both amateur and professional athletes seeking to improve their performance. Creatine also appears to increase lean body mass, although this effect can vary.
How It Works
While your muscles are at rest, normal aerobic respiration provides them with energy. They don't require much creatine phosphate for energy, and they produce more of it than they use. On the other hand, when your muscles are actively contracting, they need more ATP for energy and start using up their stores of creatine phosphate. However, they are unable make enough extra ATP to keep up with the rate at which they use it.
Muscle Fatigue
Responding to increased need, the production of ATP rises in your muscle cells, but it is limited by the rate at which oxygen can reach them. At maximum exertion, the mitochondria in your muscle cells only make about one-third of the ATP they require. Your body then shifts to anaerobic activity to make ATP, but this results in the byproduct lactic acid, which builds up and causes your muscles to fatigue.
Additional Information
Creatine supplements may slow the progress of Parkinson's disease and increase strength and endurance in conditions like amyotrophic lateral sclerosis, rheumatoid arthritis, various muscular dystrophies and congestive heart failure. Creatine supplementation by athletes is permitted by the International Olympic Committee and the National Collegiate Athletic Association, according to MedlinePlus.com. Your creatine needs depend on your size and physical activity, but supplementation is not considered necessary. Check with your doctor before you start taking creatine.