In warm, humid conditions, the thermal gradient between the skin and environment is reduced, along with the capacity for evaporative heat loss. Consequently, heat may be stored within the body during exercise. Interventions to offset heat stress may be beneficial to perception and performance.
PURPOSE: To assess whether donning a garment saturated with menthol and ethanol (M/E) could improve evaporative cooling and thermal perceptions versus water (W) or no nothing (CON) during rest and exercise in warm, humid conditions. It was hypothesised there would be no difference in rectal (Tre) and skin (Tsk) temperature, thermal imagery of the chest/back, thermal comfort (TC) and rating of perceived exertion (RPE) between M/E, W and CON, but participants would feel cooler in M/E versus W or CON.
METHODS: Six volunteers (mean [SD] 22  years old, 72.4 [7.4] kg and 173.6 [3.7] cm) completed (separate days) three, 60-minute tests in warm, humid conditions (30 °C, 70 % rh) in a balanced order. After 15-minutes of seated rest participants donned a dry (CON) or 80 mL soaked (M/E, W) long sleeve shirt appropriate to their intervention. They then undertook 30-minutes of low intensity stepping exercise at a rate of 12 steps per minute, followed by 15 minutes of seated rest. Measurements included heart rate (HR), Tre, Tsk (chest, back, forearm), thermal imaging (back/chest), thermal sensation (TS), TC and RPE. Data were reported every fifth minute as they changed from baseline and the area under the curves were compared by condition using one-way repeated measures ANOVA, with an alpha level of 0.05.
RESULTS: Tre differed by condition, with the largest heat storage response observed in M/E (p<0.05). Skin temperature at the chest/back/forearm, and thermal imaging of the back/chest all differed by condition, with the greatest rate of heat loss observed in W and M/E respectively (p<0.01). Thermal sensation differed by condition, with the coolest sensations observed in M/E (p<0.001). No other differences were observed.
CONCLUSIONS: Both M/E and W enhanced evaporative cooling compared CON, but M/E causes cooler sensations and a heat storage response, both of which are likely mediated by menthol, a well-established cold receptor TRPM8 agonist.