Perceptual, Thermoregulatory, and Performance Effects of Menthol Gel Application in Trained Triathletes Exercising in...

Topical menthol application improves thermal perception and enhances performance but reduces sweat production in hot environments. In the aquatic environment, where sweat evaporation is of limited thermoregulatory benefit (ie, minimal evaporation) and leads to dehydration and cardiovascular strain, downregulating thermoregulatory sweating may have little consequence. However, it may preserve hydration status and improve subsequent performance, especially in air (ie, after first transition in triathlon); we tested this hypothesis.

Eight trained triathletes (age 36 [5] y; height 1.77 [0.1] m; mass 73.9 [8.0] kg) completed 2 experimental conditions with prior whole-body application of menthol GEL (40 g, 3.5% menthol) contrasted to NO-GEL. The protocol comprised 30 minutes of swimming (at 85% of 400-m personal best) in tropical water (29 °C) followed by a 20-km self-paced cycling time trial. Measures were deep body temperature (gastrointestinal pill), skin temperature, sweat production, rating of perceived exertion, thermal sensation, and thermal comfort. Paired t test and analysis of variance compared the data (.05 alpha level).

Wet-bulb globe temperature equated to "red flag" conditions-heat-injury potential for all participants. Terminal gastrointestinal temperature was 38.8 °C (0.3 °C) and 38.8 °C (0.7 °C) and time-trial performance was 39:36 (04:31) and 40:53 (05:53) minutes in the GEL and NO-GEL conditions, respectively (P = .340; 95% CI, -222 to 88 s; d = -0.22). Sweat production increased in the GEL condition (1140 [257] mL) compared to the NO-GEL condition (961 [202] mL) (t = 2.482, P = .042; 95% CI, 08 to 349 mL; d = 0.77).

Menthol improved perception but increased thermoregulatory sweating and did not enhance performance (partial hypothesis support).