Biological sex does not independently influence time-dependent changes in core temperature and sweating of children exercising in uncompensable heat stress.

Abstract

To investigate the influence of biological sex, independent of differences in aerobic fitness and body fatness, on the change in gastro-intestinal temperature (∆Tgi) and whole-body sweat rate (WBSR) of children exercising under uncompensable heat stress. Seventeen boys (mean±SD; 13.7±1.3 years) and 18 girls (13.7±1.4) years) walked for 45 min at a fixed rate of metabolic heat production per kg body mass (8 W·kg-1) in 40°C and 30% relative humidity. Sex and V̇O2peak were entered into a Bayesian hierarchical general additive model (HGAM) for Tgi. Sex, V̇O2peak and the evaporative requirement for heat balance (Ereq) were entered into a Bayesian hierarchical linear regression for WBSR. For 26 (12 M, 14 F) of the 35 children with measured body composition, body fat percentage was entered in a separate HGAM and hierarchical linear regression for Tgi and WBSR respectively. Conditional on sex-specific mean V̇O2peak, ∆Tgi was 1.00°C [90% credible intervals: 0.84, 1.16] for boys and 1.17°C [1.01, 1.33] for girls, with a difference of 0.17°C [-0.39, 0.06]. When sex differences in V̇O2peak were accounted for, the difference in ∆Tgi between boys and girls was 0.01°C [-0.25, 0.22]. The difference in WBSR between boys and girls was 0.03 L·h-1 [-0.02, 0.07], when isolated from differences in Ereq. The difference in ∆Tgi between boys and girls was -0.10°C [-0.38, 0.17] when sex differences in body fat (%) were accounted for. Biological sex did not independently influence the ∆Tgi and WBSR of children exercising under uncompensable heat stress.