CAFFEINE AND ENDURANCE PERFORMANCE

Caffeine is consumed in many beverages and foods throughout the world. It is the most commonly used drug in North America and, probably, in many other countries. The short term consumption of caffeine may resul t in increased urination, gastrointestinal distress, tremors, decrease d sleep, and anxiety symptoms in certain individuals. The long term co nsumption of caffeine at < 5 cups/day does not appear to increase the risk of cancer, cardiovascular disease, peptic ulcer disease or cardia c arrhythmias. At the cellular level, caffeine is a competitive antago nist of adenosine receptors and probably acts directly on the ryanodin e receptor (Ca++ release channel) to potentiate Ca++ release from skel etal muscle sarcoplasmic reticulum. As a result of these 2 cellular me chanisms of action, caffeine causes increased lipolysis, a facilitatio n of central nervous system transmission, a reduction in plasma potass ium during exercise, an increased force of muscle contraction at lower frequencies of stimulation, and a sparing of muscle glycogen (partial ly or wholly due to an increase in free fatty acid oxidation). These m echanisms of action would predict that caffeine should be of ergogenic benefit during endurance exercise performance, especially when glycog en depletion would be rate limiting to performance. A review of the li terature suggests that caffeine at doses of approximately 6 mg/kg is n ot of ergogenic benefit to high intensity exercise performance, but si milar doses are ergogenic in endurance exercise performance. These dos es (approximately 6 mg/kg) would result in urinary caffeine concentrat ions less than the current International Olympic Committee restricted level of 12 mg/L, and consideration should be given to lowering this l evel.