Menthol as an Adjuvant to Help Athletes Cope With a Tropical Climate: Tracks From Heat Experiments With Special Focus on Guadeloupe Investigations

Abstract

Endurance and prolonged exercise are altered by hot climate. In hot and dry climate, thermoregulation processes, including evapotranspiration, normally maintain a relatively constant body core temperature. In hot and wet climate (usually called “tropical”), the decrease in evapotranspiration efficacy increases the sweating rate, which can rapidly induce severe hypohydration without efficiently reducing core temperature. The negative effects of tropical environment on long-duration exercise have been well documented, with clear demonstrations that they exceed the acclimation possibilities: both acclimated athletes and natives to tropical climate show impaired performances compared with that in neutral climate. New countermeasures, applicable during competitive events, are therefore needed to limit these negative effects. We studied the effects of several countermeasures in outdoor or natural tropical climates and noted that the easiest method to apply is cooling with cold (−1 to 3°C) beverage. Moreover, adding menthol increased the cold sensation induced by the beverage temperature, optimizing the positive effects on performance. We also demonstrated that efficient pre-cooling with cold menthol beverage requires drinking for 1 h instead of 30 min before the exercise. The optimal cooling method seems to be 1 h of cold + menthol pre-cooling ingestion followed by menthol + ice-slurry per-cooling. However, limitations should be noted: (1) the menthol concentration seems to be crucial, with positive effects for a 0.05% solution, whereas higher concentrations need to be explored; and (2) because it acts as a cold adjuvant without decreasing core temperature, menthol can lead to decreased thermoregulatory processes, thus inducing hyperthermia. Last, if menthol is added to cooling processes, athletes should first test them in training conditions for the maximal cooling effect to ensure optimal performance in competition in tropical climate.

One hour of internal precooling with cold water/menthol enhances cycling performance in a heat/wet stress environment: A pilot study

“…Despite the low temperature of the ingested solution [ 12 – 14 , 20 , 25 , 26 ] and the additive effect of menthol with cold beverage [ 12 ], our results did not show a significant difference between the Pre-30 condition (i.e., ice-slush/menthol beverage at -1°C during the last 30 min of the resting period) and Neutral condition (i.e., neutral beverage at 23°C during the 1-hour pre-exercise resting period) for performance or rectal temperature. In accordance with other studies [ 19 , 27 ], these results seem to confirm that 30 min of precooling is not enough to improve cycling performance.…”

The Impact of Wrist Percooling on Physiological and Perceptual Responses during a Running Time Trial Performance in the Heat

“…Thus, while the present data does not support the hypothesis that the use of the cooling bands would have lowered RPE and TS, the present data are to be considered in the context of altered running speed over time. Recent meta-analysis suggests that topical or ingestion of menthol, a known agonist of the “cold receptor,” TRPM8, can alter thermal sensation and/or exercise performance [ 11 ], perhaps independent of core temperature [ 41 ]. Relatedly, work by Phillips et al [ 7 ] suggests that precooling might modulate the prefrontal cortex and/or its processing of afferent feedback regarding perceptions of effort, fatigue, or skin temperature, which might support greater exercise tolerance, and ultimately an attenuation of muscle fatigue.…”

Performance effects of internal pre- and per-cooling across different exercise and environmental conditions: A systematic review

“…The exclusion criteria determined a further removal of 69 articles. Two were review articles (24,25), three had a noncrossover design (26)(27)(28), nineteen reported only physiological, cognitive or perceptual performance measures (29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47), nine had no control or placebo group (48)(49)(50)(51)(52)(53)(54)(55)(56), five were conference abstracts/posters (57-61), three were performed in clinical context (62)(63)(64), twenty-seven did not report an exclusive effect of the internal cooling and one comprised underage participants (92). Forty-three articles fulfilled the eligibility criteria and data were extracted for qualitative analysis.…”