CREATINE IN HUMANS WITH SPECIAL REFERENCE TO CREATINE SUPPLEMENTATION

Since the discovery of creatine in 1832, it has fascinated scientists with its central role in skeletal muscle metabolism. In humans, over 9 5% of the total creatine (Cr(tot)) content is located in skeletal musc le, of which approximately a third is in its free (Cr(f)) form. The re mainder is present in a phosphorylated (Cr(phos)) form. Cr(f) and Cr(p hos) levels in skeletal muscle are subject to individual variations an d are influenced by factors such as muscle fibre type, age and disease , but not apparently by training or gender. Daily turnover of creatine to creatinine for a 70kg male has been estimated to be around 2g. Par t of this turnover can be replaced through exogenous sources of creati ne in foods, especially meat and fish. The remainder is derived via en dogenous synthesis from the precursors arginine, glycine and methionin e. A century ago, studies with creatine feeding concluded that some of the ingested creatine was retained in the body. Subsequent studies ha ve shown that both Cr(f) and Cr(phos) levels in skeletal muscle can be increased, and performance of high intensity intermittent exercise en hanced, following a period of creatine supplementation. However, neith er endurance exercise performance nor maximal oxygen uptake appears to be enhanced. No adverse effects have been identified with short term creatine feeding. Creatine supplementation has been used in the treatm ent of disease where creatine synthesis is inhibited.