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

highlights
• Skin wettedness cannot predict thermal discomfort at high metabolic rates.
• Galvanic skin conductance can predict thermal discomfort.
• Galvanic skin conductance indicates internal and external sweat.
• Discomfort is related to sweat within and around the skin.
• The torso area experiences higher thermal discomfort than the extremities.

The relationship between local thermal comfort, local skin wettedness (wlocal) 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% VO2max 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% VO2max 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). wlocal, change from baseline in GSC (ΔGSC) and local thermal comfort were recorded every 5 min. The results suggest that both wlocal 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 wlocal 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 wlocal during the RUN (r2>0.95 and r2>0.94, respectively). Despite the strength of these relationships, the ability of wlocal 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 wlocal. The wlocal 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.