True, caffeine can aid sprint performances, but that's no consolation for the multi-hour performer. In addition, caffeine has a troubling tendency to empty your body of water. Its diuretic effect can do more than increase the queues at Portaloos prior to races; pre-competition caffeine could also expel enough water to raise your body temperature and heart rate during exercise and increase your risk of dehydration.

However, if you want to take in some caffeine DURING your exertions, there's no problem, according to recent research at Ohio State University. At Ohio State, six athletes cycled for three hours at an intensity of 60% V02max (74 per cent of maximal heart rate) while ingesting a carbohydrate-electrolyte sports drink which on one occasion contained caffeine and on a separate date was caffeine-free. On two other days, the subjects tried the two beverages without engaging in any exercise at all.

When no exercise was carried out, caffeine acted as a strong diuretic, hiking urine production by a hefty 31 per cent. However, during the cycling trials, it was a different story altogether. As the cyclists pedaled along, the use of a caffeinated sports drink didn't boost urine output at all, compared to drinking a caffeine-free beverage. In addition, caffeine had no effect on heart rate, body temperature, perceived effort, or overall performance. This was in spite of the fact that the athletes were swallowing the equivalent of two cups of coffee per hour during their three-hour exertions.

What does this new information really mean for endurance athletes? Taking in 'de-fizzed,' caffeinated soda during exercise, as many athletes like to do, won't increase the risk of dehydration or harm performance, as many experts have suggested. In fact, if the soda is diluted a bit with water (adding one ounce of plain water for every two ounces of soda should be about right), it will make a pretty decent sports drink. In addition, the added caffeine might actually give an athlete a little more power during a full-tilt 'kick' at the end of a race.

'Caffeine Ingested in a Fluid Replacement Beverage during Prolonged Exercise Does Not Cause Diuresis' Medicine and Science in Sports and Exercise, vol. 26(5), Supplement, p. 5204, 1994