Thermoregulation at rest and during exercise in prepubertal boys

Summary

Thermal balance was studied in 11 boys, aged 10–12 years, with various values for maximal oxygen uptake ($\dot V_{O_{2 max} }$), during two standardized sweating tests performed in a climatic chamber in randomized order. One of the tests consisted in a 90-min passive heat exposure [dry bulb temperature (T _db) 45° C] at rest. The second test was represented by a 60-min ergocycle exercise at 60% of individual$\dot V_{O_{2 max} }$ (T _db 20° C). At rest, rectal temperature increased during heat exposure similar to observations made in adults, but the combined heat transfer coefficient reached higher values, reflecting greater radiative and convective heat gains in the children. Children also exhibited a greater increase in mean skin temperature, and a greater heat dissipation through sweating. Conversely, during the exercise sweating-test, although the increase in rectal temperature did not differ from that of adults for similar levels of exercise, evaporative heat loss was much lower in children, suggesting a greater radiative and convective heat loss due to the relatively greater body surface area. Thermophysiological reactions were not related to$\dot V_{O_{2 max} }$ in children, in contrast to adults.