Creatine is often taken by athletes to help as a supplement for those wishing to gain muscle mass (bodybuilding). There are a number of forms but the most common are creatine monohydrate (creatine complexed with a molecule of water) and creatine ethyl ester (CEE). A number of methods for ingestion exist: as a powder mixed into a drink, or as a capsule or caplet. Once ingested, creatine is highly bioavailable, whether it is ingested as the crystalline monohydrate form, the free form in solution, or even in meat. Creatine salts will become the free form when dissolved in aqueous solution. Conventional wisdom recommends the consumption of creatine with high glycemic index carbohydrates.[6]

There is scientific evidence that short term creatine use can increase maximum power and performance in high-intensity anaerobic repetitive work (periods of work and rest) by 5 to 15%. This is mainly bouts of running/cycling sprints and multiple sets of low RM weightlifting. Single effort work shows an increase of 1 to 5%. This refers mainly to single sprints and single lifting of 1-2RM weights. However, some studies show no ergogenic effect at all.[7] Studies in endurance athletes have been less than promising, most likely because these activities are sustained at a given intensity and thus do not allow for significant intra-exercise synthesis of additional creatine phosphate molecules. Ingesting creatine can increase the level of phosphocreatine in the muscles up to 20%. It must be noted creatine has no significant effect on aerobic endurance, though it will increase power during short sessions of high-intensity aerobic exercise.[8][9]

Since body mass gains of about 1 kg can occur in a week's time, many studies suggest that the gain is simply due to greater water retention inside the muscle cells.[10] Other studies, however, have shown that creatine increases the activity of satellite cells, which make muscle hypertrophy possible. Creatine supplementation appears to increase the number of myonuclei that satellite cells will 'donate' to damaged muscle fibers, which increases the potential for growth of those fibers.