HYPERHYDRATION - THERMOREGULATORY EFFECTS DURING COMPENSABLE EXERCISEHEAT-STRESS

This study examined the effects of hyperhydration on thermoregulatory responses during compensable exercise-heat stress. The general approac h was to determine whether 1-h preexercise hyperhydration [29.1 ml/kg lean body mass; with or without glycerol (1.2 g/kg lean body mass)] wo uld improve sweating responses and reduce core temperature during exer cise. During these experiments, the evaporative heat loss required (E- req = 293 W/m(2)) to maintain steady-state core temperature was less t han the maximal capacity (E-max = 462 W/m(2)) of the climate for evapo rative heat lass (E-req/E-max = 63%). Eight heat-acclimated men comple ted five trials: euhydration, glycerol hyperhydration, and water hyper hydration both with and without rehydration (replace sweat loss during exercise). During exercise in the heat (35 degrees C, 45% relative hu midity), there was no difference between hyperhydration methods for in creasing total body water (similar to 1.5 liters). Compared with euhyd ration, hyperhydration did not alter core temperature, skin temperatur e, whole body sweating rate, local sweating rate, sweating threshold t emperature, sweating sensitivity, or heart rate responses. Similarly n o difference was found between water and glycerol hyperhydration for t hese physiological responses. These data demonstrate that hyperhydrati on provides no thermoregulatory advantage over the maintenance of euhy dration during compensable exercise-heat stress.