Thermoregulation in boys and men exercising at the same heat production per unit body mass.

Abstract

Child-adult thermoregulatory comparisons may be biased by differences in metabolic heat production ([Formula: see text]). We compared thermoregulatory responses of boys and men exercising at two intensities prescribed to elicit either a fixed [Formula: see text] per unit body mass (BM) or a fixed absolute [Formula: see text]. Ten boys (10-12 years) and 10 men (19-25 years) performed 4×20-min cycling at a fixed [Formula: see text] per BM (Wkg(-1)) at 35°C and 35% relative humidity (MENREL). Men also cycled (MENABS) at the same absolute [Formula: see text] (in W) as the boys. [Formula: see text] was lower in boys compared with MENREL, but similar to MENABS (mean±SD, 233.6±38.4, 396.5±72.3, 233.6±34.1W, respectively, P<0.001). Conversely, [Formula: see text] per unit BM was similar between boys and MENREL, and lower in MENABS (5.7±1.0, 5.6±0.8 and 3.3±0.3Wkg(-1), respectively; P<0.001). The change in rectal temperature was similar between boys and MENREL (0.6±0.2 vs. 0.7±0.2°C, P=0.92) but was lower in MENABS (0.3±0.2°C, P=0.004). Sweat volume was lower in boys compared to MENABS (500±173 vs. 710±150mL; P=0.041), despite the same evaporative heat balance requirement (E req) (199.1±34.2 vs. 201.0±32.7W, P=0.87). Boys and men demonstrated similar thermoregulatory responses to 80min of exercise in the heat performed at a fixed [Formula: see text] per unit BM. Sweat volume was lower in boys compared to men, despite similarities in absolute [Formula: see text] and E req.