Dilution Method of Menthol Solutions Affects Subsequent Perceptual Thermal Responses during Passive Heat Exposure in Non-Heat Acclimated Participants

Abstract

Due to its volatility, the qualitative experience of menthol may be modulated by its preparation and combination with other compounds. One such method of preparation is dilution, with two dilution methods existing within the sport and exercise science literature, where menthol is used to impart feelings of oral cooling and improve thermal comfort and sensation during heat exposure. This study compared these two dilution methods; one using a solvent the other using temperature, via a randomized counterbalanced repeated measures design (n = 12; Height: 174.0 ± 8.5 cm Mass: 73.4 ± 13.3 kg Age: 28.7 ± 8.4 y; two exposures to each solution) to assess the effect of solution and heat exposure, upon thermal comfort, thermal sensation and associated physiological parameters in non-heat acclimated participants. Thermal comfort was significantly affected by solution (p = 0.041; η2 = 0.017) and time (p < 0.001; η2 = 0.228), whereas thermal sensation was significantly affected by time only (p = 0.012; η2 = 0.133), as was tympanic temperature (p < 0.001; η2 = 0.277). Small to moderate clear differences between solutions at matched time points were also observed. These trends and effects suggest that, depending upon the dilution method employed, the resultant perceptual effects are likely impacted; this also likely depends upon the timing of menthol administration within a heat exposure session.

Menthol Mouth Rinsing Maintains Relative Power Production during Three-Minute Maximal Cycling Performance in the Heat Compared to Cold Water and Placebo Rinsing

“…Thus, ratings in the current study may have differed if participants were given a more thorough explanation of thermal comfort and sensation, where they should anchor their descriptions of each perception from and examples of when they might feel a particular number. For example, Best, et al [ 30 , 31 ], used a scenario with the participants prior to testing to distinguish between thermal comfort and thermal sensation. The scenario consisted of participants imagining lying on a sun lounger in a hot environment (e.g., a beach).…”

“…Eleven healthy non-heat-acclimated male ( n = 6) and female ( n = 5) participants (height: 171.2 ± 11.0 cm; mass: 75 ± 13 kg; age: 25 ± 5 years) were included in this study. To ensure non-heat-acclimated participation, research was conducted over autumn and winter months, with no participant travelling to hot (≥28 °C) climate for ≥two months, prior to study commencement [ 28 , 31 ]. Inclusion criteria required participants to have general fitness ability, with prior experience in exercise testing procedures and being self-reported as free from injury.…”

“…Participants wore exercise clothing in which they felt most comfortable; this was shorts or exercise tights, lightweight t-shirt and shoes. The estimated insulative values of environment appropriate sportswear for males is 0.45–0.61 clo and 0.57 clo for females [ 30 , 31 , 49 ]. Once settled on the bike prior to warm up, resting blood lactate was taken via a fingertip sample (Lactate Pro 2, Arkray Ltd., Koka-shi, Shiga, Japan).…”

“…Menthol being applied as a mouth rinse targets a smaller thermally sensitive area compared to a topical spray, or other more aggressive cooling methodologies that elicit a reduction in core body temperature. However, a greater menthol concentration could potentially eliminate variability due to individuals’ differing menthol sensitivity thresholds [ 14 , 29 , 30 , 31 ]. It is important to note that at higher concentrations menthol acts as an irritant, but when administered at appropriate concentrations and time intervals, irritation and desensitization are mitigated [ 32 , 33 ].…”

The Effect of Isolated and Combined Application of Menthol and Carbohydrate Mouth Rinses on 40 km Time Trial Performance, Physiological and Perceptual Measures in the Heat

“…This approach has previously been used to detect differences between regional thermal sensations [37]. Statistical significance was set at p < 0.05, readers are also encouraged to interpret these data alongside typical and ecologically meaningful variation in performance and other measures, e.g., the smallest worthwhile change of all perceptual measures was considered 0.5 arbitrary units [38,39].…”