The topography of eccrine sweating in humans during exercise

Abstract

The purpose of this study was to investigate the distribution of steady-state sweating rates (m _sw), during stressful exercise and heat exposures. Six men completed 42-min trials: 2-min rest and 40-min cycling at 40% peak power in 36.6° C (relative humidity 46.0%). The m _sw, was monitored using ventilated capsules at the forehead, and at three additional sites. Repeat trials allowed monitoring from eleven skin surfaces. Auditory canal temperature (T_ac) and 11 skin temperatures were measured. After normalising m _sw to the forehead response within subjects, differences in T _ac and onset time thresholds, and transient and steady-state m _sw were examined. The pooled, lower torso m _sw onset [mean 45.5 (SEM 42.0) s] preceded that of the head [mean 126.5 (SEM 34.8) s, P<0.05], but was not significantly different from the legs [mean 66.6 (SEM 25.7) s], upper torso [mean 80.2 (SEM 36.8) s] or arms [mean 108.6 (SEM 31.2) s]. Transient m _sw did not differ among regions (P=0.16). Mean, steady-state forehead m _sw [3.20 (SEM 0.51) mg · cm⁻² · min⁻¹]was not significantly greater than the scapula, forearm, hand, stomach and lower back m _sw (in descending order), but was greater than the chest [1.6 (SEM 0.2)], upperarm [1.6 (SEM 0.2)], calf [1.5 (SEM 0.3)] and thigh m _sw [1.0 (SEM 0.2), P<0.05 for all comparisons]. The results did not support the caudal-to-rostral sweat onset evident during supine, resting heat stress. Equivalent T _ac sweat thresholds existed between sites, while steady-state m _sw topography varied among subjects and was not dominated by central regions.