Body regional influences of l-menthol application on the alleviation of heat strain while wearing firefighter’s protective clothing

Abstract

The purpose of this study was to investigate the influences of menthol application according to the amount of surface area on physiological and psychological heat strains, along with body regional influences. Male students underwent two stages of experiments: [Experiment 1] Cutaneous thermal threshold test at rest on eight body regions with/without a 0.8% menthol application at T (a) 28°C and 50% RH; [Experiment 2] Six exercise tests with/without a 0.8% menthol spray at T (a) 28°C and 40% RH, while wearing firefighter's protective clothing (No menthol, PC(NO); Face and neck menthol, PC(FN); Upper body menthol, PC(UP); Whole body menthol application, PC(WB)) or wearing normal clothing (No menthol, NC(NO); Upper body menthol, NC(UP)). Experiment 1 showed that menthol caused no significant influence on cutaneous warm thresholds, while menthol applications evoked earlier detection of cool sensations, especially on the chest (P = 0.043). Experiment 2 revealed that NC(UP), PC(UP) and PC(WB) caused lower mean skin temperature, especially with higher peripheral vasoconstrictions on the extremities at rest. During exercise, NC(UP), PC(UP) and PC(WB) induced greater and earlier increases in rectal temperatures (T (re)) and a delayed sweat response, but lessened psychological burdens (P < 0.05). Both physiological and psychological effects of PC(FN) were insignificant. For a composite analysis, individual Menthol Sensitivity Index at cooling in Experiment 1 had significant relationships with the threshold for T (re) increase and changes in heart rate in NC(UP) of Experiment 2 (P < 0.05). Our results indicate that menthol's topical influence is body region-dependent, as well as depending on the exposed body surface area.

Relieving thermal discomfort: Effects of sprayed L‐menthol on perception, performance, and time trial cycling in the heat

“…It would also have been valuable to directly measure blood flow rather than a surrogate such as T skin . We are clearly assuming that any vasoconstriction induced by L-menthol application would result in lower surface T skin , and consequently, result in a higher deep body temperature as has been shown at higher concentrations of L-menthol (4.6% L-menthol sediment; Kounalakis et al, 2010; 0.80% L-menthol spray; Lee et al, 2012). In the present study, it is evident that the L-menthol effectively uncoupled the relationship with T skin and thermal perception shown by the lower thermal perceptions after spraying with a similar magnitude of drop in T skin between sprays.…”

“…Lee et al. () subsequently supported this effect using a 0.80% L‐menthol spray in firefighters wearing protective clothing. In a previous experiment, we found no evidence that deep T body increased at a faster rate after L‐menthol was applied immediately before the start of self‐paced exercise (Barwood et al., ), but this might not remain the case when L‐menthol is applied toward the end of exercise when maximal vasodilatation at the skin is more likely (Charkoudian, ) and the consequent effects of vasoconstriction for deep T body may be more marked.…”

“…These neurons feature a highly sensitive receptor, TRPM8, which is activated by temperatures ranging from 8 to 28 °C (Jordt et al., ), and by chemical compounds such as L‐menthol (McKemy et al., ; Peier et al., ). Body sprays comprising a relatively low concentration of L‐menthol (0.05–0.80% L‐menthol in solution) have been shown to induce improvements in TS and TC during fixed intensity [Gillis et al., (0.05 and 0.20% L‐menthol); Lee et al., (0.80% L‐menthol)] and self‐paced exercise [Barwood et al., , (0.05% and 0.20% L‐menthol)] in the heat and have been marketed as performance enhancing in combination with dissolved alcohol at low concentrations (e.g., Physicool™, London, UK; 0.20%). However, independent experimental evidence in support of the ergogenic effect of L‐menthol has yet to be identified (Barwood et al., ).…”

The effect of practical cooling strategies on physiological response and cognitive function during simulated firefighting tasks in a smoke-diving room

“…The CG (Golafshan, Iran) was used in the neck and forehead and, based on Lee et al, 33 reports the amount of CG coated over neck and forehead was on average 0.77 ± 0.20 g/6.25 cm 2 in body surface area. The CV (Microgard, UK), which was very light, was worn over a cotton T-shirt and was 100% polyester (PES) fabric coated with phase change material (PCM capsules) (Figure 2).…”

The influence of a menthol and ethanol soaked garment on human temperature regulation and perception during exercise and rest in warm, humid conditions

“…In an effort to enhance evaporative heat loss and lessen warm sensations in the heat, some commercial companies have added menthol and ethanol to Menthol, Ethanol and Thermoregulation in Humans Gillis et al, their water-based skin cooling products. Menthol is a chemical compound that activates the cold receptor TRPM8 (McKemy et al, 2002;Peier et al, 2002) and elicits cool sensations when applied to the skin of heat stressed humans (Barwood et al, 2012;2014;Gillis et al, 2010;Lee et al, 2012). But menthol also induces a heat storage response that is in part mediated by a reduction in cutaneous skin blood flow (Gillis et al, 2015) and possibly a withdrawal of sudomotor function i.e.…”