[Creatine: the nutritional supplement for exercise - current concepts].

Abstract

Creatine, a natural nutrient found in animal foods, is alleged to be an effective nutritional ergogenic aid to enhance sport or exercise performance. It may be formed in kidney and liver from arginina and glicina. Creatine may be delivered to the muscle, where it may combine readily with phosphate to form creatine phosphate, a high-energy phosphagen in the ATP-CP system, and is stored. The ATP-CP energy system is important for rapid energy production, such as in speed and power events. Approximately 120 g of creatine is found in a 70 kg male, 95% in the skeletal muscle. Total creatine exists in muscle as both free creatine (40%) and phosphocreatine (60%). It is only recently that a concerted effort has been undertaken to investigate its potential ergogenic effect relative to sport or exercise performance. It does appear that oral creatine monohydrate may increase muscle total creatine, including both free and phosphocreatine. Many, but not all studies suggest that creatine supplementation may enhance performance in high intensity, short-term exercise task that are dependent primarily on the ATP-CP energy system, particularly on laboratory test involving repeated exercise bouts with limited recovery time between repetitions. Short-term creatine supplementation appears to increase body mass, although the initial increase is most likely water associated with the osmotic effect of increased intramuscular total creatine. Chronic creatine supplementation in conjunction with physical training involving resistance exercise may increase muscle mass. However, confirmatory research data are needed. Creatine supplementation up to 8 weeks, with high doses, has not been associated with major health risks; with low doses, it was demonstrated that in 5 years period supplementation, there are no adverse effects. The decision to use creatine as a mean to enhance sport performance is left to the description to the individual athlete.