Nutritional ergogenic aids and exercise performance

The use of nutritional supplements in sport is widespread and few serious a thletes do not, at some stage in their career, succumb to the temptation to experiment with one or more nutritional supplements. Nutritional ergogenic aids are aimed primarily at enhancing performance (either by affecting ene rgy metabolism or by an effect on the central nervous system), at increasin g lean body mass or muscle mass by stimulation of protein synthesis and at reducing body fat content. Although not strictly ergogenic (i.e. capable of enhancing work performance), supplements aimed at increasing resistance to infection and improving general health are seen by athletes as important i n reducing the interruptions to training that minor illness and infection c an cause. Creatine is perhaps the most widely used supplement in sport at t he moment. Supplementation can increase muscle creatine phosphate levels an d, although not all published studies show positive results, there is much evidence that performance of short-term high-intensity exercise can be impr oved by supplementation. Ingestion of large doses of bicarbonate can enhanc e performance of exercise where metabolic acidosis may be a limiting factor , but there is a significant risk of adverse gastrointestinal side effects. Caffeine can also improve performance, in part by a stimulation of fatty a cid mobilization and sparing of the body's limited carbohydrate stores, but also via direct effects on muscle and possibly by central nervous system e ffects on the perception of effort and fatigue. Carnitine plays an essentia l role in fatty acid oxidation in muscle but, although supplements are used by athletes, there is no good evidence of a beneficial effect of supplemen tation. None of these products contravenes the International Olympic Commit tee regulations on doping in sports, although caffeine is not permitted abo ve a urine concentration of 12 mg/l. Supplementation is particularly preval ent among strength and power athletes, where an increase in muscle mass can benefit performance. Protein supplements have not been shown to be effecti ve except in those rare cases where the dietary protein intake is otherwise inadequate. Individual amino acids, especially ornithine, arginine and glu tamine, are also commonly used, but their benefit is not supported by docum ented evidence. Cr and hydroxymethylbutyrate are also used by strength athl etes, but again there are no well-controlled studies to provide evidence of a beneficial effect. Athletes use a wide variety of supplements aimed at i mproving or maintaining general health and vitamin and mineral supplementat ion is widespread. There is a theoretical basis, and limited evidence, to s upport the use of antioxidant vitamins and glutamine during periods of inte nsive training, but further evidence is required before the use of these su pplements can be recommended.