Effects of 24-h sleep deprivation on whole-body heat exchange in young men during exercise in the heat.

Sleep deprivation has been associated with impaired thermoregulatory function. However, whether these impairments translate to changes in whole-body heat exchange during exercise-heat stress remains unknown. Therefore, following either a night of normal sleep or 24 h of sleep deprivation, 10 young men (mean (SD): 23 (3) years) completed three 30-min bouts of semi-recumbent cycling at increasing fixed rates of metabolic heat production (150, 200, 250 W/m), each separated by a 15-min rest in dry heat (40 °C, ~ 13% relative humidity). Rates (W/m) of whole-body total heat exchange (dry + evaporative) were measured continuously and expressed as peak responses [mean of the final 5-min of exercise at the highest metabolic heat production (250 W/m)]. Body heat storage was quantified as the temporal summation of heat production and loss. Core temperature, indexed by rectal temperature, was measured continuously. Relative to normal sleep, sleep deprivation did not modify whole-body heat exchange (evaporative (-6 [-18, 5] W/m; P = 0.245), or dry (7 [-5, 19] W/m; P = 0.209; sleep deprivation-normal sleep mean difference [95%CIs]) and therefore total heat loss (1 [-14, 15] W/m; P = 0.917). There were no differences in either the change in body heat storage (-9 [-67, 49] kJ; P = 0.732) or change in core temperature (0.1 [-0.1, 0.3] °C; P = 0.186) between conditions. Overall, we showed that 24-h sleep deprivation did not influence whole-body dry or evaporative heat exchange, resulting in no differences in total whole-body heat exchange or body heat storage in young adults during exercise under hot-dry conditions.