Influence of the timing of fluid ingestion on temperature regulation during exercise.

The purpose of this investigation was to determine whether the timing of fluid ingestion affects thermoregulation during exercise-heat stress. On four occasions, seven endurance-trained cyclists [age 25 +/- 2 (SE) yr, body weight 70.5 +/- 3.3 kg, maximal O2 uptake (VO2max) 4.69 +/- 0.11 l/min] performed 140 min of cycle ergometer exercise at 62-66% of VO2max in a hot environment (33 degrees C dry bulb, 51% relative humidity, wind speed 2.5 m/s). The subjects drank 1,173 +/- 44 ml of a carbohydrate-electrolyte beverage after 0 min (D0), 40 min (D40), or 80 min (D80) of exercise or consumed the same total volume in small aliquots throughout exercise (DT). The exercise-heat stress resulted in calculated sweating rates of approximately 1,200 ml/h and a body weight loss of 2.9 +/- 0.1% after 140 min of exercise. After fluid intake in the D0, D40, and D80 trials, there was a time period (approximately 40 min) in which the increases in serum osmolality and sodium concentration and the reduction in blood volume were attenuated. During that same time period, there was an attenuated rise in esophageal temperature (Tes; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)