Creatine is an amino acid (a protein building block) which is absorbed into the bloodstream in the small intestine and excreted as the by-product creatinine in the urine. Creatine in the form of creatine phosphate (phosphocreatine) is an important form of high-energy phosphate found in skeletal muscle cells. During high-intensity exercise lasting for a short time (15 to 30 seconds), phosphocreatine is broken down into phosphate and creatine. The energy released is used to regenerate ATP, the primary source of energy. As phosphocreatine becomes depleted, output power drops because ATP cannot be regenerated fast enough. Therefore, more energy is available for use. In short-duration, high-intensity anaerobic sports such as weight lifting or sprinting, it is logical that more creatine phosphate in the muscles would allow greater ATP regeneration to produce more energy and increase performance.

Research has shown that taking creatine monohydrate supplements enhances performance for athletes who participate in high-intensity, short-duration sports. Several studies have been recently conducted to study a variety of sports and various dosages of creatine. The results are generally concurrent. After an initial "loading" phase of about a week, a "maintenance" phase keeps most athletes' muscle concentrations of creatine high enough to see noticeable changes in endurance and strength, and also an increase in lean muscle mass. However, some individuals are genetically predisposed to have high stores of creatine already in their muscles, or have a high efficiency or inefficiency in producing ATP. These people will not see a dramatic ergogenic (energy-producing) effect from creatine monohydrate supplementation.

About half of an individual's daily need of creatine is synthesized in the liver, kidneys, and pancreas from the amino acids glycine, arginine, and methionine. The other half is provided from the diet.

Meat or fish are the best natural sources of creatine. There is about 1 g of creatine in a half pound of raw meat. However, for purposes of "loading" the skeletal muscles to gain ergogenic benefits, it is not feasible to get extra creatine from the diet alone. Supplementation is necessary.

There are three different forms of creatine. Creatine is primarily stored in the skeletal muscles as free creatine and phosphocreatine. Creatine monohydrate is the form primarily used for supplementation to increase the skeletal muscles' stores of both free creatine and the phosphorylized form used to fuel energy release during the conversion of ATP.

Creatine monohydrate is available in a variety of forms. The most common form is a powder which is ingested by mixing with juice or water. Generally, about 1 tsp. provides a 5 g dose of creatine monohydrate. Liquid creatine monohydrate, a more recently marketed preparation, is now competing with the powdered form. Claimed benefits of the liquid form are faster absorption and convenience over the powdered variety. Creatine monohydrate is also available in tablets, capsules, energy "bars," chews, drink mixes, and other preparations. Since combining creatine monohydrate with glucose is reported to be more effective than taking creatine alone, there are many preparations with differing combinations of creatine and glucose or other carbohydrates.

• Primarily used by athletes as a supplement to "load" muscle stores of creatine to improve strength, endurance, and lean muscle mass for high-intensity, short-duration exercise
• May reduce blood lipids
• May improve glucose metabolism
• Reduces muscle wasting in postsurgical patients
• May benefit heart patients by increasing myocardial metabolism and reducing fibrillation as well as allowing increased exercise capacity
• May provide anti-inflammatory and analgesic activity

The typical loading regimen for the average weight athlete consists of taking creatine monohydrate supplements in the dose of 5 g, qid (20 g/day) for seven days, depending on body weight. After that, the maintenance phase consists of 2 to 5 g/day to sustain the stores of creatine in the muscles.

The only well-documented side effect has been weight gain. This is due to water being stored in the muscle cells (volumization), general water weight gain, and also an increase in lean muscle tissue.

Unsubstantiated side effects which have been reported include greater incidence of muscle cramping, strains, and pulls; gastrointestinal distress; kidney impairment; and liver damage. However, studies have been done which negate these claims.

Not useful to increase performance in endurance (aerobically oriented) exercise.

There has been a report of an ischemic stroke in a male weight lifter who ingested combinations of Ma Huang (ephedra alkaloids) (40 to 60 mg/day), caffeine (400 to 600 mg/day), and creatine monohydrate (6000 mg/day) (Vahedi et al. 2000). The combination of the CNS stimulants with creatine may have contributed to the ischemic attack. Until this case, creatine alone had not been associated with cardiovascular side effects.

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