Thermoregulatory responses during prolonged exercise in the heat are not affected by fluid temperatures ranging from 5 to 35℃

Abstract

 We examined the effects of different fluid temperatures of 5, 15, 25, and 35℃ on thermoregulatory responses during prolonged exercise in the heat because it is speculated that fluid at temperatures of between 5 and 15℃, as recommended by the Japan Sports Association, would have different effects on thermoregulatory parameters. Six men from an university track and field team performed 4 sets of cycling exercise (one set=15-min exercise with a 5-min rest period) at 50%VO₂max under conditions of 32℃ and 60% relative humidity. The volume of water provided was 80% of the total sweat rate in the non-drinking (control) trial divided by 4 equal aliquots. The increase in rectal temperature, mean skin temperature and mean body temperature during exercise showed no significant differences across all the fluid temperatures. Similarly, local sweat rate, skin blood flow and cutaneous vascular conductance were similar among the conditions. These results suggest that iso-volumetric fluids with varying temperatures (5-35℃) have no effect on rectal temperature and heat loss responses during prolonged exercise in a hot environment.