Nutritional ergogenic aids and exercise performance

Abstract

The use of nutritional supplements in sport is widespread and few serious athletes 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 energy metabolism or by an effect on the central nervous system), at increasing 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 in reducing the interruptions to training that minor illness and infection can cause. Creatine is perhaps the most widely used supplement in sport at the moment. Supplementation can increase muscle creatine phosphate levels and, although not all published studies show positive results, there is much evidence that performance of short-term high-intensity exercise can be improved by supplementation. Ingestion of large doses of bicarbonate can enhance performance of exercise where metabolic acidosis may be a limiting factor, but there is a signi®cant risk of adverse gastrointestinal side effects. Caffeine can also improve performance, in part by a stimulation of fatty acid mobilization and sparing of the body's limited carbohydrate stores, but also via direct effects on muscle and possibly by central nervous system effects on the perception of effort and fatigue. Carnitine plays an essential role in fatty acid oxidation in muscle but, although supplements are used by athletes, there is no good evidence of a bene®cial effect of supplementation. None of these products contravenes the International Olympic Committee regulations on doping in sports, although caffeine is not permitted above a urine concentration of 12 mg/l. Supplementation is particularly prevalent among strength and power athletes, where an increase in muscle mass can bene®t performance. Protein supplements have not been shown to be effective except in those rare cases where the dietary protein intake is otherwise inadequate. Individual amino acids, especially ornithine, arginine and glutamine, are also commonly used, but their bene®t is not supported by documented evidence. Cr and hydroxymethylbutyrate are also used by strength athletes, but again there are no well-controlled studies to provide evidence of a bene®cial effect. Athletes use a wide variety of supplements aimed at improving or maintaining general health and vitamin and mineral supplementation is widespread. There is a theoretical basis, and limited evidence, to support the use of antioxidant vitamins and glutamine during periods of intensive training, but further evidence is required before the use of these supplements can be recommended.

The effect of caffeine ingestion on functional performance in older adults

“…All participants habitually ingested caffeine although none were heavy caffeine users (mean ± SD of caffeine consumption = 149.2 ± 58 mg/day, range = 90-210 mg/day). Caffeine intake was established using a 24 hour recall questionnaire (25). All participants completed a health history questionnaire to ensure that they met all inclusion criteria.…”

The athlete’s diet: nutritional goals and dietary strategies

“…A wide range of experimental models and subject groups have been employed, and it is difficult to determine consistent patterns that could account for the effects seen in some studies but not in others. There is strong support for effects on repeated sprints, with less conclusive evidence for effects on single sprints and on muscle strength (Maughan, 1999;Williams et al 1999). Many studies and much anecdotal information support the suggestion that acute supplementation with creatine is associated with a prompt gain in body mass.…”

“…A few supplements have been the subject of closer scrutiny, and there is evidence to support the use of creatine, caffeine, bicarbonate and perhaps also a small number of other compounds. Comprehensive reviews can be found elsewhere (Maughan, 1999(Maughan, , 2000a, and only a few individual supplements will be considered here.…”

Evaluating the effects of caffeine and sodium bicarbonate, ingested individually or in combination, and a taste-matched placebo on high-intensity cycling capacity in healthy males

“…Participants that completed the study habitually consumed caffeine, but were not heavy caffeine users (125 ± 95 mg/day). Caffeine intake was measured using a 24 hour recall questionnaire (Maughan 1999). …”