Caffeine and exercise - Metabolism, endurance and performance

Caffeine is a common substance in the diets of most athletes and it is now appearing in many new products, including energy drinks, sport gels, alcoho lic beverages and diet aids. It can be a powerful ergogenic aid at levels t hat are considerably lower than the acceptable limit of the International O lympic Committee and could be beneficial in training and in competition. Ca ffeine does not improve maximal oxygen capacity directly, but could permit the athlete to train at a greater power output and/or to train longer. It h as also ben shown to increase speed and/or power output in simulated race c onditions. These effects have been found in activities that last as little as 60 seconds or as long as 2 hours. There is less information about the ef fects of caffeine on strength; however, recent work suggests no effect on m aximal ability, but enhanced endurance or resistance to fatigue. There is n o evidence that caffeine ingestion before exercise leads to dehydration, io n imbalance, or any other adverse effects. The ingestion of caffeine as coffee appears to be ineffective compared to d oping with pure caffeine. Related compounds such as theophylline are also p otent ergogenic aids. Caffeine may act synergistically with other drugs inc luding ephedrine and anti-inflammatory agents. It appears that male and fem ale athletes have similar caffeine pharmacokinetics, i.e., for a given dose of caffeine, the time course and absolute plasma concentrations of caffein e and its metabolites are the same. In addition, exercise or dehydration do es not affect caffeine pharmacokinetics. The limited information available suggests that caffeine non-users and users respond similarly and that withd rawal from caffeine may not be important. The mechanism(s) by which caffein e elicits its ergogenic effects are unknown, but the popular theory that it enhances fat oxidation and spares muscle glycogen has very little support and is an incomplete explanation at best. Caffeine may work, in part, by cr eating a more favourable intracellular ionic environment in active muscle. This could facilitate force production by each motor unit.