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

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 degrees C for 30 min (equilibrium period) and then in conditions where air temperature (Ta) was decreased linearly from 28 to 15 degrees C (at a constant rate of 0.22 degrees 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 [Tre, mean 37.30 (SEM 0.10) and mean 37.43 (SEM 0.14) degree C in the boys and the men, respectively] or for the respective skin temperatures (except for the forehead), but metabolic heat production (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 declining Ta, 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 M as Ta decreased was significantly lower for the boys (P < 0.01) largely because of a higher M before the cold exposure. Thus, the mean 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 the Ta was lowered, Tre in the boys started falling (P < 0.001), whereas the Tre in the young men did not change for 60 min. The Tre 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) degree C at the end of the exposure]. It was concluded that when Ta was lowered, the prepubertal boys appeared to vasoconstrict more in their limbs and to be somewhat more hypothermic, compared to the young men.