Influence of age and biological sex on sweating in children exercising in warm and hot environments with comparison to adults

Age and biological sex have been suggested to affect sweating during exercise, but studies that have compared the local sweating response between boys and girls of different ages are limited. We standardized exercise intensity to the rate of metabolic heat production per body surface area and compared local sweat rate and the sweating onset threshold between boys, girls, adult males and adult females using Bayesian hierarchical modelling. Sixty-one children (29 females; 10-16 years old) and 20 adults (9 females; 19-37 years old) walked for 45 min at a fixed rate of metabolic heat production per body surface area (300 W·m-2) in WARM (30°C, 40% relative humidity) and/or HOT (40°C, 30% relative humidity) environments. Differences in local sweat rate between boys and girls were ≤0.03 mg·cm-2·min-1 (90% credible intervals: -0.14, 0.08) in WARM and ≤0.08 mg·cm-2·min-1 (-0.05, 0.23) in HOT, indicating no meaningful sex differences in children. In HOT, the local sweat rate of the back was 1.17 mg·cm-2·min-1 (1.05, 1.28) for boys, 1.09 mg·cm-2·min-1 (0.76, 1.41) for adult males, 1.09 mg·cm-2·min-1 (0.99, 1.19) for girls and 1.01 mg·cm-2·min-1 (0.72, 1.27) for adult females. Sweating onset threshold times differed by ≤0.6 min (-0.2, 1.4) between sexes at the back in WARM. An increase in age of 4 years was associated with a 1.1 min (0.1, 2.0) and 0.8 min (0.1, 1.5) greater sweating onset threshold time of boys and girls, respectively. In conclusion, age and biological sex did not meaningfully influence the local sweating response and onset threshold of children and adults exercising at 300 W·m-2. KEY POINTS: Age and biological sex have been suggested to influence sweating during exercise, but their effect might be confounded by exercise intensity prescription and the consequent sweating requirement between individuals of differing body size. By standardizing exercise intensity to the rate of metabolic heat production per body surface area (in metres squared), we elicited an equivalent evaporative requirement for heat balance and compared local sweat rate and the sweating onset threshold between boys, girls, adult males and adult females exercising in warm and hot conditions. Our findings demonstrate that biological sex did not meaningfully influence the local sweating response and onset threshold time of children exercising at 300 W·m-2 in warm and hot environments. In a hot environment, older children had a greater local sweat rate compared with younger children, but this was not evident when comparing children and adults.