Thermoregulatory responses of prepubertal boys and young men in changing temperature linearly from 28 to 15°C

Abstract

To examine thermoregulatory responses of prepubertal children to cold stress, 11 boys (aged 8 years) and 11 young men (aged 19–23 years), wearing only trunks, participated in this study. They sat in air at 28°C for 30 min (equilibrium period) and then in conditions where air temperature (T _a) was decreased linearly from 28 to 15°C (at a constant rate of 0.22°C · min⁻¹) for 60 min, at a fixed relative humidity of 65%. In the equilibrium period there was no significant difference between the groups for rectal temperature [T _re, mean 37.30 (SEM 0.10) and mean 37.43 (SEM 0.14)°C in the boys and the men, respectively] or for the respective skin temperatures (except for the forehead), but metabolic heat production ($\dot M$) was significantly greater for the boys [mean 57.1 (SEM 1.2) and mean 52.0 (SEM 0.9)W. m⁻²,P <0.005]. With decliningT _a, the skin temperatures decreased in both groups (P <0.001), but the decrease was significantly greater for the boys (P < 0.05), especially on the limbs as represented by the thigh and forearm. No significant correlations were observed between the limb skin temperatures compared to surface area-to-mass ratio or limb skinfold thicknesses in either group. The rate of increase in$\dot M$ asT _a decreased was significantly lower for the boys (P < 0.01) largely because of a higher$\dot M$ before the cold exposure. Thus, the mean$\dot M$ during the cold exposure did not differ between the groups [mean 63.6 (SEM 1.1) and mean 61.6 (SEM 1.1) W · m⁻² in boys and men, respectively]. When theT _a was lowered,T _re in the boys started falling (P < 0.001), whereas theT _re in the young men did not change for 60 min. TheT _re during the 60-min exposure was significantly lower (P < 0.001) for the boys [mean 37.01 (SEM 0.13) and mean 37.48 (SEM 0.18)°C at the end of the exposure]. It was concluded that whenT _a was lowered, the prepubertal boys appeared to vasoconstrict more in their limbs and to be somewhat more hypothermic, compared to the young men.