Caffeine is widely reported to be an ergogenic aid i.e. a substance that improves the capacity to do work or exercise. Costill and his co-workers were the first to show that 330 mg caffeine administered 1 hour before exercise at 80% of maximal oxygen consumption on a bicycle ergometer increased time to exhaustion. Since then, the vast majority of published studies have shown that caffeine prolongs time to exhaustion or enhances performance in prolonged, moderate- to high-intensity exercise lasting between 30 and 120 minutes. A study of the endurance of trained distance runners during prolonged exercise at 85% of maximal oxygen consumption showed that the optimal caffeine dose is between 3 and 6mg/kg body weight. Evidence for an ergogenic effect of caffeine in short-term, high-intensity exercise lasting between 1 and 10 minutes is not so compelling. However, 6 or 9 mg caffeine/kg body weight was effective in improving endurance in oarsmen and oarswomen participating in a simulated 2,000 m rowing event. It has been shown that habitual caffeine consumption has a minimal impact on the ergogenic properties of caffeine. However, while 4.45 mg caffeine/kg body weight was effective at increasing endurance in adults exercising at 85% of maximal oxygen consumption, the same dose of caffeine in coffee was not.

The mechanism of the ergogenic effect of caffeine is a matter of debate. It has been proposed that caffeine stimulates catecholamine release which in turn stimulates adipose tissue lipolysis. This increases the concentration of circulating free fatty acids and hence their oxidation and so spares muscle glycogen (a carbohydrate store). However, caffeine can have ergogenic effects without elevating catecholamine release so other mechanisms must operate. Caffeine can stimulate the mobilisation of intracellular calcium in muscle cells in vitro and this could enhance muscle contraction and endurance, improve neuromuscular transmission and increase peak force generation in vivo . It has also been suggested that the beneficial effects of caffeine on concentration, fatigue and alertness might also play a role in mediating the ergogenic effect.

It has been shown that caffeine consumption can improve athletic performance in numerous endurance events including swimming, cycling and women’s tennis . The International Olympic Committee (IOC) removed caffeine from its list of banned substances in January 2004.

The diuretic effect of caffeine may be a particular disadvantage for athletes competing in humid climates where the risk of dehydration is high or in endurance events where dehydration has a greater effect on performance. Athletes are often advised to avoid tea and coffee for these reasons but the diuretic effect of caffeine is likely to be small in those accustomed to its use.