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Excerpt
The purpose of this investigation was to examine the effects of rehydration with glycerol and to study the endocrine, cardiovascular and thermoregulatory responses during subsequent exercise. Eight endurance-trained male cyclists(age: 24±1 yr, VO2peak: 61.4±0.8 ml·kg-1·min-1) completed three dehydration-rehydration experimental trials which differed only with regard to the rehydration treatment. Prior to each experimental day, subjects dehydrated to -4% of their body weight, by exercise and water restriction. The experimental treatments were: no fluid (NF); glycerol (G) bolus (1g/kg), followed by water; and water alone (W). Rehydration (3% body weight) was given over an 80-min period. Thirty minutes after rehydration, subjects cycled (74% VO2peak) to exhaustion in a hot (37 °C) environment. Vasopressin and plasma renin activity decreased during rehydration in the W and G trials, but no differences were found between trials. Plasma osmolality was increased during the G trial compared to the W trial throughout the experiment. For the G trial plasma volume expanded (p<0.05) during rehydration and remained elevated (p<0.05) during exercise. Exercise time to exhaustion was longest(p<0.05) during the G trial (33±4 min) compared to both W(27±3 min) and NF (19±3 min) trials. Cutaneous vascular conductance was found to be significantly elevated (p<0.05) during the G trial, but glycerol administration had no other thermoregulatory or cardiovascular benefit compared to the W and NF. Fluid-regulating hormones were increased during exercise (except atriopeptin), but no differences were found between the G and W trials. These data suggest that glycerol has little or no effect on fluid regulating factors during rehydration or exercise, and the improved performance in G was probably due to the greater plasma volume during exercise.
