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

Abstract

Purpose

Child–adult thermoregulatory comparisons may be biased by differences in metabolic heat production ( \(\dot{H}_{\text{p}}\) ). We compared thermoregulatory responses of boys and men exercising at two intensities prescribed to elicit either a fixed \(\dot{H}_{\text{p}}\) per unit body mass (BM) or a fixed absolute \(\dot{H}_{\text{p}}\) .

Methods

Ten boys (10–12 years) and 10 men (19–25 years) performed 4 × 20-min cycling at a fixed \(\dot{H}_{\text{p}}\) per BM (W kg⁻¹) at 35 °C and 35 % relative humidity (MEN_REL). Men also cycled (MEN_ABS) at the same absolute \(\dot{H}_{\text{p}}\) (in W) as the boys.

Results

\(\dot{H}_{\text{p}}\) was lower in boys compared with MEN_REL, but similar to MEN_ABS (mean ± SD, 233.6 ± 38.4, 396.5 ± 72.3, 233.6 ± 34.1 W, respectively, P < 0.001). Conversely, \(\dot{H}_{\text{p}}\) per unit BM was similar between boys and MEN_REL, and lower in MEN_ABS (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 MEN_REL (0.6 ± 0.2 vs. 0.7 ± 0.2 °C, P = 0.92) but was lower in MEN_ABS (0.3 ± 0.2 °C, P = 0.004). Sweat volume was lower in boys compared to MEN_ABS (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).

Conclusion

Boys and men demonstrated similar thermoregulatory responses to 80 min of exercise in the heat performed at a fixed \(\dot{H}_{\text{p}}\) per unit BM. Sweat volume was lower in boys compared to men, despite similarities in absolute \(\dot{H}_{\text{p}}\) and E _req.

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