Perceptual, thermoregulatory and performance effects of menthol gel application in trained triathletes exercising in hot conditions

Purpose: 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 (i.e., minimal evaporation) and leads to dehydration and cardiovascular strain, downregulating thermoregulatory sweating may have little consequence but preserve hydration status and improve subsequent performance especially in air (i.e., after 1st transition in triathlon); we tested this hypothesis. Method: Eight trained triathletes (36 (5) yrs; height 1.77 (0.1) m; 73.9 (8.0) kg) completed two experimental conditions with prior whole-body application of menthol GEL (40g, 3.5% menthol) contrasted to NO-GEL. The protocol comprised 30-minute swimming (@85% 400 m PB) in tropical water (29 °C) followed by a 20 km self-paced cycling time-trial (TT). Measures were deep body temperature (gastrointestinal pill; TGI), skin temperature (Tskin), sweat production, RPE, thermal sensation (TS) and comfort (TC). Paired (t-test) and ANOVA compared data (0.05 alpha level). Results. Wetbulb globe temperature equated to ‘red flag’ conditions - heat injury potential for all. Terminal TGI was 38.8 (0.3) °C and 38.8 (0.7) °C and TT 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 = -.22). Sweat production increased in the GEL condition 1140 (257) mL; NO-GEL 961 (202) mL (t = 2.482, p = .042; 95% CI 08 to 349 mL; d = .77). Conclusion. Menthol improved perception but increased thermoregulatory sweating and didn’t enhance performance (partial hypothesis support).