Biological Sex Does Not Influence Core Temperature Change and Sweating of Children Exercising in a Warm Environment

PURPOSE: To investigate the associations of biological sex and aerobic fitness (i.e., V̇O2peak) on the change in gastro-intestinal temperature (∆Tgi) and whole-body sweat rate (WBSR) of children exercising in warm conditions.

METHODS: Thirty-eight children (17 boys (mean [SD]; 13.7 [1.2] years); 21 girls (13.6 [1.8] years)) walked for 45 min at a fixed rate of metabolic heat production (8 W·kg-1) in 30 °C and 40% relative humidity. Biological sex and relative V̇O2peak were entered as predictors into a Bayesian hierarchical general additive model (HGAM) for Tgi. For a subsample of 13 girls with measured body composition, body fat percent was entered into a separate HGAM for Tgi. Sex, V̇O2peak and the evaporative requirement for heat balance (Ereq) were entered into a Bayesian hierarchical linear regression for WBSR.

RESULTS: Mean ∆Tgi for boys was 0.71 °C [90% credible intervals: 0.60, 0.82] and for girls 0.78 °C [0.68, 0.88]. A predicted 20 mL·kg-1·min-1 higher V̇O2peak resulted in a 0.19 °C [-0.03, 0.43] and 0.24 °C [0.07, 0.40] lower ∆Tgi in boys and girls respectively. A predicted ~13% lower body fat in the subsample of girls resulted in a 0.15 °C [-0.12, 0.45] lower ∆Tgi. When Ereq was standardized to the grand mean, the difference in WBSR between boys and girls was -0.00 L·h-1 [-0.06, 0.06] and a 20 mL·kg-1·min-1 higher predicted V̇O2peak resulted in a mean difference in WBSR of -0.07 L·h-1 [-0.15, 0.00].

CONCLUSIONS: Biological sex did not independently influence ∆Tgi and WBSR in children. However, a higher predicted V̇O2peak resulted in a lower ∆Tgi of children, which was not associated with a greater WBSR, but may be related to differences in body fat percent between high and low fitness individuals.