Dieticians, physiologists, athletic trainers, and physicians have recommended refraining from caffeine intake when exercising because of possible fluid-electrolyte imbalances and dehydration.
To assess how 16-hour rehydration is affected by caffeine ingestion.
59 college-age men.
Subjects consumed a chronic caffeine dose of 0 (placebo), 3, or 6 mg · kg−1 · day−1 and performed an exercise heat-tolerance test (EHT) consisting of 90 minutes of walking on a treadmill (5.6 km/h) in the heat (37.7 °C).
There were no between-group differences immediately after and 16 hours after EHT in total plasma protein, hematocrit, urine osmolality, specific gravity, color, and volume. Body weights after EHT and the following day (16 hours) were not different between groups (P > .05).
Hydration status 16 hours after EHT did not change with chronic caffeine ingestion.
The authors are with the Human Performance Laboratory, University of Connecticut, Storrs, CT 06269-1110.