Comparison Of Core Temperature And Thermoregulatory Sweating Between Boys And Girls Exercising In Uncompensable Heat

PURPOSE: Females have been previously reported to be thermoregulatory disadvantaged when compared to males. However, previous research comparing males and females has often been confounded by physical and physiological differences between sexes, such as morphology and aerobic fitness. Our understanding of sex-mediated differences in thermoregulation within children is limited further, as few studies have included direct comparisons between boys and girls. Therefore, the purpose of this study was to compare the change in core temperature and thermoregulatory sweating of boys and girls exercising in an uncompensable environment. METHODS: 17 boys (age: 13.4 ± 1.5 y, peak oxygen uptake [V̇O2peak]: 50.2 ± 10.7 mL⸳kg-1⸳min-1) and 18 girls (age: 13.5 ± 1.7 y, V̇O2peak: 46.6 ± 6.7 mL⸳kg-1⸳min-1) completed 45 min of treadmill walking at a fixed rate of metabolic heat production per unit body mass (8 W⸱kg-1) and per body surface area (300 W⸱m-2) in 40 °C and 30% relative humidity. Core temperature (Tcore) was measured continuously via gastro-intestinal telemetric pill. Local sweat rate (LSR) was measured using a ventilated sweat capsule affixed to the upper back. RESULTS: In the 8 W⸱kg-1 trial, participant sex, age and V̇O2peak were entered as predictor variables into a general linear model with ∆Tcore as the dependent variable. A significant effect was found for V̇O2peak (-0.02 °C per mL⸳kg-1⸳min-1, CI: -0.04, -0.00, P = 0.015), but not for sex (-0.01 °C for male, CI: -0.28, 0.26, P = 0.925) or age (0.03 °C per year, CI: -0.06, 0.12, P = 0.531). In the 300 W⸱m-2 trial, participant sex, age and V̇O2peak were entered as predictor variables with end-exercise LSR (n = 34) as the dependent variable. No significant effect was found for V̇O2peak (0.01 mg·cm-2·min-1 per mL⸳kg-1⸳min-1, CI: -0.00, -0.02, P = 0.250) sex (0.00 mg·cm-2·min-1 for male, CI: -0.18, 0.18, P = 0.981) or age (0.05 mg·cm-2·min-1 per year, CI: -0.00, 0.11, P = 0.071). CONCLUSION: When exercising at a fixed rate of metabolic heat production per unit body mass in 40 °C and 30% relative humidity, a greater V̇O2peak attenuated the ∆Tcore across both sexes. Furthermore, our data indicate a lack of any sex-mediated difference in thermoregulatory sweating between boys and girls during prolonged exercise in an uncompensable condition.