Caffeine and endurance performance.
The belief among athletes that caffeine is an ergogenic aid is common, and several governing bodies of sport have barred use of the drug during competition. At the cellular level, caffeine has been implicated to affect the translocation of calcium in muscle, promote an increase in cellular levels of cyclic AMP and cause a blockade of adenosine receptors in the central nervous system. The general systemic effect of caffeine is to cause central nervous system arousal, mobilisation of free fatty acids and other metabolites, and possibly enhance the contractile status of muscle. At present, the scientific community remains divided as to whether caffeine ingestion will indeed produce an ergogenic effect upon sport performance. Some evidence suggests that caffeine may improve performance in events relying upon strength and power; however, the lack of in vivo research in humans makes it difficult to form firm conclusions. In addition, reports concerning caffeine's effect on VO2max and performance during incremental exercise are not in agreement. On the other hand, recent studies suggest that caffeine might indeed have ergogenic potential in endurance events (e.g. marathon running). It is hypothesised that the mechanism behind these findings is related to the increased availability of free fatty acids for muscle metabolism which has a glycogen-sparing effect.