Creatine supplementation: analysis of ergogenic value, medical safety, and concerns

Creatine is an amino acid which is synthesized endogenously from glycine, arginine, methionine or obtained in small quantities from the diet from meat and fish. Creatine is primarily stored in the muscle as free creatine and phosphocreatine. Short term creatine supplementation (15 to 25 g/d for 5 to 7-d) has been reported to increase total creatine content by 15 to 30% (e.g. 127 to 149 mmol/kg dry mass) and phosphocreatine stores by 10 to 40% (e.g. 67 to 91 mmol/kg dry mass). The increased availability of creatine and phosphocreatine have been reported to maintain adenosine triphosphate levels during high intensity exercise and facilitate recovery from repetitive bouts of high intensity exercise. Short-term creatine supplementation has been reported to improve maximal power/strength (5-15%), work performed during sets of maximal effort muscle contractions (5-15%), single-effort sprint performance (1-5%), and work performed during repetitive sprint performance (5-15%). Moreover, long-term supplementation of creatine or creatine containing supplements (15 to 25 g/d for 5 to 7-d and 2 to 25 g/d thereafter for 7 to 84-d) has been reported to promote significantly greater gains in strength, sprint performance, and fat free mass during training in comparison to matched-paired controls. Consequently, creatine has become one of the most popular nutritional supplements marketed to athletes in recent times. While not all studies report ergogenic benefits, most studies indicate that creatine is an effective and safe nutritional supplement. However, concerns have been recently expressed in the popular literature regarding unknown long-term side effects and anecdotal reports of greater incidence of muscle cramping/injury. This paper will provide a comprehensive overview of the literature regarding creatine supplementation as well as examine the validity of recent concerns raised regarding creatine supplementation.