Local sweating on the forehead, but not forearm, is influenced by aerobic fitness independently of heat balance requirements during exercise

The present study investigated the influence of maximal oxygen uptake ( ) on local steady‐state sudomotor responses to exercise, independently of evaporative requirements for heat balance (Ereq). Eleven fit (F; 61.9 ± 6.0 ml kg−1 min−1) and 10 unfit men (UF; 40.4 ± 3.8 ml kg−1 min−1) cycled for 60 min at an air temperature of 24.5 ± 0.8°C and ambient humidity of 0.9 ± 0.3 kPa at a set metabolic heat production per unit surface area, producing the same Ereq in all participants (BAL trial) and, in a second trial, at 60% of . During the BAL trial, absolute power (F 107 ± 2 and UF 102 ± 2 W; P= 0.126), Ereq (F 175 ± 5 and UF 176 ± 9 W m−2; P= 0.855), steady‐state whole‐body sweat rate (F 0.44 ± 0.02 and UF 0.47 ± 0.02 mg cm−2 min−1; P= 0.385) and local sweat rate on the arm (F 0.29 ± 0.03 and UF 0.35 ± 0.03 mg cm−2 min−1; P= 0.129) were not different between groups; however, local sweat rate on the forehead in UF (1.67 ± 0.20 mg cm−2 min−1) was almost double (P= 0.002) that of F (0.87 ± 0.11 mg cm−2 min−1). Heart rate, ratings of perceived exertion and relative exercise intensity were also significantly greater in UF (P < 0.05). There was a trend towards an elevated minute ventilation in UF (P= 0.052), while end‐tidal was significantly lower in UF (P= 0.028). At 60% , absolute power (F 174 ± 6 and UF 110 ± 5 W; P < 0.001), Ereq (F 291 ± 14 and UF 190 ± 17 W m−2; P < 0.001), steady‐state whole‐body sweat rate (F 0.84 ± 0.05 and UF 0.53 ± 0.03 mg cm−2 min−1; P < 0.001) and local sweat rate on the arm (F 0.75 ± 0.04 and UF 0.35 ± 0.03 mg cm−2 min−1; P < 0.001) and on the forehead (F 2.92 ± 0.42 and UF 1.68 ± 0.23 mg cm−2 min−1; P= 0.022) were all significantly greater in F compared with UF. Heart rate and ratings of perceived exertion were similar at all time points (P > 0.05). Significantly greater minute ventilation (P < 0.001) and end‐tidal responses (P= 0.017) were found in F. In conclusion, aerobic fitness alters local sweating on the forehead, but not the forearm, independently of evaporative requirements for heat balance, and may be the result of differential control of sweating in these skin areas associated with the relative intensity of exercise.