Describing individual variation in local sweating during exercise in a temperate environment

It has been previously demonstrated that the individual variation in whole-body sweat rate is described by differences in each participant’s heat balance status. It was hypothesized that the individual variation in local sweat rate of the forehead (LSR_head) and forearm (LSR_arm) would be similarly described using a whole-body heat balance approach, specifically the ratio of evaporation required for heat balance relative to the maximum evaporation possible (i.e. E _req:E _max). Twelve males cycled at 60% \( \dot{V}{\text{O}}_{{ 2 {\text{max}}}} \) for 60 min at 24.9 ± 0.5°C, 31 ± 14% relative humidity. Rectal (T _re) and aural canal (T _au) temperatures as well as mean skin temperature (\( \bar{T}_{\text{sk}} \)), metabolic energy expenditure (M) and rate of external work (W) were measured throughout. In addition, whole-body sweat rate at steady state (WBSR_ss) was estimated using the change in body mass over the last 15 min of exercise, with LSR_head and LSR_arm estimated using technical absorbent patches applied between the 50th and 55th minute. WBSR_ss significantly correlated with M–W (r = 0.66, P = 0.021), E _req (r = 0.69, P = 0.013) and E _req:E _max (r = 0.87, P < 0.001); LSR_head was significantly correlated with E _req:E _max (r = 0.82, P = 0.001), but not M–W (r = 0.31, P = 0.328) or E _req (r = 0.38, P = 0.227); and LSR_arm significantly correlated with E _req (r = 0.62, P = 0.031) and E _req:E _max (r = 0.78, P = 0.003) but not M–W (r = 0.56, P = 0.059). None of WBSR_ss, LSR_head or LSR_arm significantly correlated with any variations in T _re, T _au or \( \bar{T}_{\text{b}} \) (i.e. 0.8T _re + 0.2\( \bar{T}_{\text{sk}} \)). Secondary analyses also demonstrated that both LSR_head (r = 0.79, P = 0.002) and LSR_arm (r = 0.89, P < 0.001) correlated with WBSR_ss. In conclusion, the individual variation in WBSR_ss, LSR_head and LSR_arm is described by the ratio of E _req relative to E _max.