Hydration during exercise in warm, humid conditions: effect of a caffeinated sports drink.
Caffeine is regarded as a diuretic despite evidence that hydration is not impaired with habitual ingestion. The purpose of this study was to determine whether a caffeinated sports drink impairs fluid delivery and hydration during exercise in warm, humid conditions (28.5 degrees C, 60% relative humidity). Sixteen cyclists completed 3 trials: placebo (P), carbohydrate-electrolyte (CE), and caffeinated (195 mg/L) sports drink (CAF+CE). Subjects cycled for 120 min at 60-75%VO2max followed by 15 min of maximal-effort cycling. Heart rate and rectal temperature were similar until the final 15 min, when these responses and exercise intensity were higher with CAF+CE than with CE and P. Sweat rate, urine output, plasma- volume losses, serum electrolytes, and blood deuterium-oxide accumulation were not different. Serum osmolality was higher with CAF+CE vs. P but not CE. The authors conclude that CAF+CE appears as rapidly in blood as CE and maintains hydration and sustains cardiovascular and thermoregulatory function as well as CE during exercise in a warm, humid environment.
Millard-Stafford
Mindy L
ML
School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA 30332-0356, USA.
Cureton
Kirk J
KJ
Wingo
Jonathan E
JE
Trilk
Jennifer
J
Warren
Gordon L
GL
Buyckx
Maxine
M
D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D018592:Cross-Over Studies; D004232:Diuretics / Q000494:pharmacology*; D004311:Double-Blind Method; D004326:Drinking; D006801:Humans; D006813:Humidity; D008297:Male; D010101:Oxygen Consumption; D015532:Rehydration Solutions / Q000494:pharmacology*; D013546:Sweating / Q000502:physiology; D013696:Temperature; D014882:Water-Electrolyte Balance / Q000187:drug effects* / Q000502:physiology
D000697:Central Nervous System Stimulants; D004232:Diuretics; D015532:Rehydration Solutions; D002110:Caffeine