A comparison of galvanic skin conductance and skin wettedness as indicators of thermal discomfort during moderate and high metabolic rates

The relationship between local thermal comfort, local skin wettedness (w_local) and local galvanic skin conductance (GSC) in four body segments during two different exercise intensities was compared in 10 males. In a balanced order, participants walked at 35% VO_2max for 45 min (WALK) (29.0±1.9°C, 29.8±3.6% RH, no wind) in one test and in a separate test ran at 70% VO_2max for 45 min (RUN) (26.2±2.1°C, 31.1±7.0% RH, no wind). During both tests, participants wore a loose fitting 100% polyester long sleeve top and trouser ensemble with a low resistance to heat and vapour transfer (total thermal resistance of 0.154 m² K W⁻¹ and total water vapour resistance of 35.9 m² Pa W⁻¹). w_local, change from baseline in GSC (ΔGSC) and local thermal comfort were recorded every 5 min. The results suggest that both w_local and ΔGSC are strong predictors of thermal comfort during the WALK when sweat production is low and thermal discomfort minimal (r²>0.78 and r²>0.71, respectively). Interestingly, during the RUN w_local plateaued at ~0.6 to 0.8 due to the high sweat production, whilst ΔGSC gradually increased throughout the experiment. ΔGSC had a similar relationship with thermal comfort to w_local during the RUN (r²>0.95 and r²>0.94, respectively). Despite the strength of these relationships, the ability of w_local to predict local thermal comfort accurately dramatically reduces in the exponential part of the curve. In a situation of uncompensated heat stress such as high metabolic rate in hot climate, where sweat production is high, ΔGSC shows to be a better predictor of local thermal comfort than w_local. The w_local data shows regional differences in the threshold which triggers local discomfort during the WALK than RUN; lower values are found for upper arms (0.22±0.03 and 0.28 ±0.22) and upper legs (0.22±0.11 and 0.22±0.10), higher values for upper back (0.30±0.12 and 0.36 ±0.10) and chest (0.27±0.10 and 0.39 ±0.32), respectively. However, no regional differences in the threshold of discomfort are found in the ?GSC data. Instead, the data suggests that the degree of discomfort experienced appears to be related to the amount of sweat within and around the skin (as indirectly measured by ΔGSC) at each body site.