Enhancement of Exercise Capacity in the Heat With Repeated Menthol-Spray Application

Purpose. Exercise performance is impaired in the heat and a contributing factor to this decrement is thermal discomfort. Menthol-spraying of skin is one means of alleviating thermal discomfort but has yet to be shown to be ergogenic using single spray applications. We examined whether repeated menthol-spraying could relieve thermal discomfort, reduce perception of exertion and improve exercise performance in hot (35ºC), dry (22% RH) conditions; we hypothesised it would. Method. Eight trained cyclists completed two separate conditions of fixed intensity (FI) cycling (50% PMax) for 45-minutes before a test to exhaustion (TTE; 70% PMax) with 100 mL of menthol-spray (0.20% menthol) or control-spray applied to the torso after 20 and 40-minutes. Perceptual (thermal sensation (TS), thermal comfort (TC), RPE) performance (TTE duration), thermal variables (skin temperature (Tskin), rectal temperature (Trec), cardiac frequency (fc)) and sweating were measured. Data were compared using ANOVA to 0.05 alpha level. Results. Menthol-spray improved TS (‘cold’ sensation cf ‘warm/hot’ after first spraying; p=.008) but only descriptively altered TC (‘comfortable’ cf ‘uncomfortable’; p=.173). Sweat production (994 (380) mL cf 1180 (380); p=.020) mL and rate (827 (327)mL·hr-1 cf 941 (319)mL·hr-1; p=.048) lowered. TTE performance improved (4.6 (1.74) cf 2.4 (1.55) minutes (p=.004). Menthol-spray effects diminished despite repeated applications indicating increased contribution of visceral thermoreceptors to thermal perception. Conclusion. Repeated menthol-spray improves exercise capacity but alters thermoregulation potentially conflicting behavioural and thermoregulatory drivers; care should be taken with its use. Carrying and deploying menthol-spray would impose a logistical burden which needs consideration against performance benefit.