Local differences in sweat secretion from the head during rest and exercise in the heat
Thermal sweating from the human torso accounts for about half of the whole-body sweat secretion, yet its intra-segmental distribution has not been thoroughly examined. Therefore, the aim of the current study was to provide a detailed description of the distribution of eccrine sweating within the torso during passively-induced (water-perfusion garment: 40ÃÂÃÂÃÂÃÂ°C) and progressively increasing, exercise-related thermal strain (36ÃÂÃÂÃÂÃÂ°C, 60% relative humidity). Sudomotor function was measured in ten males using ventilated sweat capsules (3.16 cm2) attached to twelve sites on the ventral (four), lateral (three) and dorsal (four) torso, and upper shoulder surfaces. Sweating increased asymptotically in all sites, with the final core temperature averaging 39.7ÃÂÃÂÃÂÃÂ°C (ÃÂÃÂÃÂÃÂ±0.1) and heart rates being 181 b min1 (ÃÂÃÂÃÂÃÂ±2). During exercise, the mean torso sweat rate averaged 1.35 mgcm2min1, with sweating from the lateral torso surfaces generally being the lowest. Each of the between-site comparisons with the lateral torso differed significantly (P < 0.05), except for comparisons with the chest (P = 0.051) and shoulder (P > 0.05). The intra-segmental differences between the lateral torso and the chest, abdomen, upper- and lower-back areas were significantly accentuated during exercise. From these data, it is evident that the torso is another region that does not have a uniform distribution of thermally-induced sweating. Thus, it is no longer acceptable for researchers, modellers, sweating manikins engineers or clothing manufacturers to assume that the sweat rates for all local sites within any body segment are equivalent.