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

The independent influence of peak oxygen uptake (Vo(? peak)) on changes in thermoregulatory responses during exercise in a neutral climate has not been previously isolated because of complex interactions between Vo(? peak), metabolic heat production (H(prod)), body mass, and body surface area (BSA). It was hypothesized that Vo(? peak) does not independently alter changes in core temperature and sweating during exercise. Fourteen males, 7 high (HI) Vo(? peak): 60.1 ± 4.5 ml·kg?1·min?1; 7 low (LO) Vo(? 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% Vo(? 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% Vo(2 peak); P = 0.001). At 60% Vo(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 Vo(? peak).