Thermoregulation in hyperhydrated men during physical exercise

Summary

The influence of hyperhydration on thermoregulatory function was tested in 8 male volunteers. The subjects performed cycle exercise in the upright position at 52%V _{O 2max} for 45 min in a thermoneutral (Ta=23° C) environment. The day after the control exercise the subjects were hyperhydrated with tap water (35 ml · kg⁻¹ of body weight) and then performed the same physical exercise as before.

Total body weight loss was lower after hyperhydration (329±85 g) than during the control exercise (442±132 g),p<0.05. The decrease in weight loss after hyperhydration was probably due to a decrease in dripped sweat (58±64 and 157±101 g,p<0.05). With hyperhydration delay in onset of sweating was reduced from 5.8±3.2 to 3.7±2.0 min (p<0.05), and rectal temperature increased less (0.80±0.20 and 0.60±0.10° C,p<0.01). The efficiency of sweating was higher in hyperhydrated (81.4%) than in euhydrated subjects (57.1%),p<0,01. It is concluded that hyperhydration influences thermoregulatory function in exercising men by shortening the delay in onset of sweating and by decreasing the quantity of dripped sweat. As a result, the increases in body temperature in hyperhydrated exercising men are lower than in normally hydrated individuals.