Can evaporative cooling attenuate physiological and perceptual responses during exercise in Hot/Dry and Warm/Humid environments?

This study evaluated the effects of evaporative cooling using a water-soaked inner t-shirt with a ventilation garment on physiological and perceptual responses during walking in Hot/Dry (40°C, 30% relative humidity) and Warm/Humid (32°C, 80% relative humidity) environments (wet-bulb globe temperature [WBGT] 31.5°C). Eight men performed a 60-min moderate-intensity exercise protocol under control (CON, fan-off of a ventilation jacket while wearing a dry inner t-shirt) and evaporative cooling conditions (EVA, fan-on of a ventilation jacket while wearing an inner t-shirt soaked with 350 ml of tap water) in each environment. Rectal temperature was ~0.4°C lower during exercise in EVA than CON in both Hot/Dry (37.7 ± 0.4 vs. 38.1 ± 0.3°C, p=0.001) and Warm/Humid (37.8 ± 0.4 vs. 38.2 ± 0.4°C, p=0.002), with no difference between environments. Whole-body sweat loss in EVA was halved compared to CON in both Hot/Dry (0.56 ± 0.12 vs. 1.08 ± 0.23 kg, p<0.001) and Warm/Humid (0.47 ± 0.10 vs. 1.12 ± 0.21 kg, p<0.001). Thermal sensation and discomfort were lower in EVA than in CON in both environments (both p<0.05). Thus, wearing a water-soaked inner t-shirt with a ventilation garment helps mitigate thermophysiological and perceptual responses in environments where ambient temperature exceeds skin temperature and in high humidity (≤ WBGT 31.5°C).