The Effect of 24-Hours Sleep Deprivation on Whole-Body Heat Loss During Exercise-Heat Stress in Young and Older Males

Abstract

Sleep deprivation has been associated with impaired thermoregulatory function in young adults, though its impact on whole-body heat loss during exercise-heat stress remains unclear. Furthermore, older adults, who are more susceptible to heat-related illnesses due to age-related impairments in heat loss capacity, often experience sleep disturbances. Yet, the effects of sleep deprivation on older adults’ physiological capacity to dissipate heat has not been assessed. To explore the effects of sleep deprivation on thermoregulation in different age groups, two studies were conducted. In the first study, 10 young males (mean [SD]: 23 [3] years) completed three 30-min bouts of semi-recumbent cycling at progressively increasing rates of metabolic heat production (150, 200, 250 W/m²), with 15-min rest periods in between, under dry heat conditions (40°C, ~13% relative humidity). Exercise-heat stress tests followed by either a night of normal sleep or total (24-hour) sleep deprivation. Rates of whole-body heat loss (dry + evaporative) were continuously measured, as were body heat storage and core temperature (indexed by rectal temperature). This study showed that 24-hour sleep deprivation did not appreciably affect total heat loss, body heat storage, or core temperature in young adults during exercise-heat stress. The second study involved 10 older males (mean [SD]: 61 [4] years) who underwent the same protocol. Unlike in young adults, sleep deprivation was associated with reduced peak whole-body total heat loss (-12 [-20, -3] W/m²; P=0.010) and increased heat storage (0.60 [0.32, 0.89] kJ/min; P=0.002) compared to normal sleep. While evaporative heat loss and dry heat gain did not significantly differ between sleep conditions, the overall reduction in total heat loss suggested an impaired thermoregulatory response in older adults, putting them at greater risk for heat-related illness. In conclusion, while sleep deprivation does not appear to alter whole-body heat loss and body heat storage in young adults, it did result in impairments in older adults as assessed during exercise in hot, dry conditions. Altogether, these findings highlight the greater susceptibility of older individuals to potentially elevated levels of heat strain during exercise in the heat when sleep deprived. Our findings emphasize the importance of adequate sleep for safe exercise in hot environments, particularly in older populations.