The Effect Of Sleep Deprivation On Thermoregulation In Older Adults During Exercise-Heat Stress

Sleep deprivation has been shown to cause a deterioration in physical and cognitive function leading to performance reductions. While some reports suggest that it can cause impairments in thermoregulation, others have shown no effect. These disparate findings may in part be due to differences in the duration of the sleep deprivation employed and or the level of heat stress assessed. Further, prior reports have been limited to the evaluation of local heat loss responses of skin blood flow and sweating which may not accurately reflect whole-body heat loss. Additionally, no study to our knowledge has assessed responses in older adults who may be at greater risk of heat-related illness. PURPOSE: To assess the effect of 24-h of sleep deprivation on heat loss capacity in older men during exercise-heat stress. METHODS: On separate days, following either a night of normal sleep or 24-h of sleep deprivation, eight older men (mean [SD], age: 62 [2] yrs), completed an exercise heat-stress test consisting of three 30-min bouts of exercise at increasing fixed rates of metabolic heat production of 150, 200, and 250 W/m2, each separated by 15-minutes rest in the heat (40 °C, 15% relative humidity). Rates of whole-body heat loss (dry and evaporative heat loss, via direct calorimetry), metabolic heat production (via indirect calorimetry) and change in core (rectal) temperature (ΔTrec, difference from pre-exercise resting) were measured continuously and expressed as peak responses (mean of final 5-minutes of the final exercise bout; 250 W/m2). Responses between conditions were compared using paired samples t-tests (α = 0.05). RESULTS: Relative to a normal night of sleep there were no differences in evaporative (282 [36] vs. 276 [31] W/m2) or dry heat loss (-66 [15] vs.-67 [18] W/m2) following sleep deprivation at the end of exercise (both p > 0.42). As such, whole-body heat loss did not differ between a normal night of sleep and sleep deprivation (216 [26] vs. 209 [19] W/m2, p = 0.31). Consequently, body heat storage (92 [36] vs. 96 [26] kJ, p = 0.62) and the ΔTrec were similar between the normal and sleep deprived conditions (1.2 [0.3] and 1.2 [0.4] °C, p > 0.69). CONCLUSION: We showed that 24-h of sleep deprivation was not associated with a decrease in heat loss capacity in older males during exercise heat stress. Natural Sciences and Engineering Research Council of Canada and Mitacs