Heat Stress with once vs thrice daily exposures to heat.

There is an underrepresentation of females in thermoregulatory research and there has been limited research investigating flexible heat acclimation strategies. Therefore, the purpose of this study was to determine the sex differences and effect of periodic vs sustained heat exposures during heat acclimation on core body temperature. Males and females were divided into two exposure groups and underwent 90 minutes of heat acclimation (38°C, 60% RH) at an absolute intensity on a treadmill (1.6 m·s-1, 5% grade) for 1 week. A sustained group completed the single 90-minute session continuously daily. A periodic group completed three 30-minute sessions 3 hours apart daily. Therefore, total heat exposure was matched. On days 1, 4, and 7 a telemetry pill was ingested at least 4 hours prior to exercise. Peak core temperature was tracked, and the area under the curve (AUC) of core temperature over time was calculated. Post-heat exposure measures for the sustained group were taken during the 6 hours following exposure. Post-heat exposure measures for the periodic group were taken in the 2 hours following each exposure. AUC was calculated using the trapezoid method. This study shows that there is not a sex-dependent capacity to heat acclimate; however, there are thermoregulatory differences between sexes before and during heat acclimation. The time course of experienced heat stress is an important consideration to make when coming up with heat acclimation strategies. When under varied heat acclimation schedules, a sufficient amount of time at an elevated core temperature must be reached in order to elicit adaptions associated with heat acclimation.