Influence of Biological Sex and Fitness on Core Temperature Change and Sweating in Children Exercising in Warm Conditions

Abstract

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.