Large differences in peak oxygen uptake do not independently alter changes in core temperature and sweating during exercise

Abstract

The independent influence of peak oxygen uptake (V̇o_{2 peak}) on changes in thermoregulatory responses during exercise in a neutral climate has not been previously isolated because of complex interactions between V̇o_{2 peak}, metabolic heat production (H_prod), body mass, and body surface area (BSA). It was hypothesized that V̇o_{2 peak} does not independently alter changes in core temperature and sweating during exercise. Fourteen males, 7 high (HI) V̇o_{2 peak}: 60.1 ± 4.5 ml·kg⁻¹·min⁻¹; 7 low (LO) V̇o_{2 peak}: 40.3 ± 2.9 ml·kg⁻¹·min⁻¹ matched for body mass (HI: 78.2 ± 6.1 kg; LO: 78.7 ± 7.1 kg) and BSA (HI: 1.97 ± 0.08 m²; LO: 1.94 ± 0.08 m²), cycled for 60-min at 1) a fixed heat production (FHP trial) and 2) a relative exercise intensity of 60% V̇o_{2 peak} (REL trial) at 24.8 ± 0.6°C, 26 ± 10% RH. In the FHP trial, H_prod was similar between the HI (542 ± 38 W, 7.0 ± 0.6 W/kg or 275 ± 25 W/m²) and LO (535 ± 39 W, 6.9 ± 0.9 W/kg or 277 ± 29 W/m²) groups, while changes in rectal (T_re: HI: 0.87 ± 0.15°C, LO: 0.87 ± 0.18°C, P = 1.00) and aural canal (T_au: HI: 0.70 ± 0.12°C, LO: 0.74 ± 0.21°C, P = 0.65) temperature, whole-body sweat loss (WBSL) (HI: 434 ± 80 ml, LO: 440 ± 41 ml; P = 0.86), and steady-state local sweating (LSR_back) ( P = 0.40) were all similar despite relative exercise intensity being different (HI: 39.7 ± 4.2%, LO: 57.6 ± 8.0% V̇o_{2 peak}; P = 0.001). At 60% V̇o_{2 peak}, H_prod was greater in the HI (834 ± 77 W, 10.7 ± 1.3 W/kg or 423 ± 44 W/m²) compared with LO (600 ± 90 W, 7.7 ± 1.4 W/kg or 310 ± 50 W/m²) group (all P < 0.001), as were changes in T_re (HI: 1.43 ± 0.28°C, LO: 0.89 ± 0.19°C; P = 0.001) and T_au (HI: 1.11 ± 0.21°C, LO: 0.66 ± 0.14°C; P < 0.001), and WBSL between 0 and 15, 15 and 30, 30 and 45, and 45 and 60 min (all P < 0.01), and LSR_back ( P = 0.02). The absolute esophageal temperature (T_es) onset for sudomotor activity was ∼0.3°C lower ( P < 0.05) in the HI group, but the change in T_es from preexercise values before sweating onset was similar between groups. Sudomotor thermosensitivity during exercise were similar in both FHP ( P = 0.22) and REL ( P = 0.77) trials. In conclusion, changes in core temperature and sweating during exercise in a neutral climate are determined by H_prod, mass, and BSA, not V̇o_{2 peak}.