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

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