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

TOPHAM, T. H., J. W. SMALLCOMBE, H. A. BROWN, B. CLARK, A. P. WOODWARD, R. D. TELFORD, O. JAY, and J. D. PÉRIARD. Influence of Biological Sex and Fitness on Core Temperature Change and Sweating in Children Exercising in Warm Conditions. Med. Sci. Sports Exerc., Vol. 56, No. 4, pp. 697- 705, 2024. Purpose: This study aimed to investigate the associations of biological sex and aerobic fitness (i.e., VO ^. _2peak) on the change in gastrointestinal temperature (ΔT _gi) and whole-body sweat rate (WBSR) of children exercising in warm conditions. Methods: Thirty-eight children (17 boys, mean ± SD = 13.7 ± 1.2 yr; 21 girls, 13.6 ± 1.8 yr) 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 VO ^. _2peak were entered as predictors into a Bayesian hierarchical generalized additive model for T _gi. For a subsample of 13 girls with measured body composition, body fat percent was entered into a separate hierarchical generalized additive model for T _gi. Sex, VO ^. _2peak, and the evaporative requirement for heat balance (E _req) were entered into a Bayesian hierarchical linear regression for WBSR. Results: The mean ΔT _gi for boys was 0.71°C (90% credible interval = 0.60–0.82) and for girls 0.78°C (0.68–0.88). A predicted 20 mL·kg ⁻¹·min ⁻¹ higher VO ^. _2peak resulted in a 0.19°C (−0.03 to 0.43) and 0.24°C (0.07–0.40) lower ΔT _gi in boys and girls, respectively. A predicted ~13% lower body fat in the subsample of girls resulted in a 0.15°C (−0.12 to 0.45) lower ΔT _gi. When E _req was standardized to the grand mean, the difference in WBSR between boys and girls was −0.00 L·h ⁻¹ (−0.06 to 0.06), and a 20-mL·kg ⁻¹·min ⁻¹ higher predicted VO ^. _2peak resulted in a mean difference in WBSR of −0.07 L·h ⁻¹ (−0.15 to 0.00). Conclusions: Biological sex did not independently influence ΔT _gi and WBSR in children. However, a higher predicted VO ^. _2peak resulted in a lower ΔT _gi 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.