- Claude Bernard -

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Caffeine does not appear to benefit short term, high intensity exercise (eg. sprinting)
Because each person responds differently to caffeine, don't assume you'll perform better with a caffeine-boost. You might just end up nauseated, coping with a "coffee stomach," or suffering from caffeine jitters at a time when you're already nervous and anxious.
Although caffeine does not appear to significantly alter water balance or body temperature during exercise, dehydration is a potential concern because caffeine is a mild diuretic.

The affects of caffeine on performance have proven significant enough to result in some regulation of the stimulant.
Caffeine is one of the best-tested ergogenic aids and is known to help athletes train harder and longer.
Caffeine stimulates the brain and contributes to clearer thinking and greater concentration.
A low-to-moderate dose of caffeine between 3 and 6 mg appears to be sufficient for enhancing performance in a maximal sustained endurance effort.