The effects of swilling an l(−)-menthol solution during exercise in the heat

Abstract

We have previously demonstrated that provision of a cold fluid (4 degrees C) during exercise in the heat increases fluid intake and improves exercise capacity when compared to a control fluid (19 degrees C). The present study investigated whether these positive effects could simply be replicated with a cooling agent, menthol. Nine healthy, non-acclimatised males (25 +/- 7 years; .VO(2max): 54 +/- 5 ml kg(-1) min(-1)) cycled to exhaustion at 65% of their peak aerobic power output at 34 degrees C, swilling 25 ml of either an L: (-)-menthol (0.01%) or orange-flavoured placebo solution every 10 min, whilst water was available ad libitum; all fluids were kept at 19 degrees C. Eight out of nine subjects cycled for longer whilst swilling with menthol and this resulted in a 9 +/- 12% improvement in endurance capacity. Rectal temperatures rose by 1.7 degrees C during exercise with the same time course in both conditions, whilst skin temperature remained largely unchanged. Swilling with menthol resulted in hyperventilation by 8 +/- 10 L min(-1) and reduced central (cardiopulmonary) ratings of perceived exertion by 15 +/- 14%. No differences between trials were observed for heart rate, oxygen uptake or carbon dioxide production, blood concentrations of glucose or lactate, sweat rate or volume of water ingested. We conclude that a change in the sensation of oropharyngeal temperature during exercise in the heat significantly affects endurance capacity, ventilation and the (central) sense of effort.

The Development of a Menthol Solution for Use during Sport and Exercise

“…Habitual menthol use may alter the threshold at which TRPM8 channels and the trigeminal nerve are stimulated [37][38][39][40], ultimately habituating thermal sensation [37,38]. Despite no statistically significant differences in the present investigation, menthol concentrations of 0.095-0.105% may lead to small increases in trigeminal stimulation, concomitantly conferring benefits such as an increase in ventilation [3,16], reduced thermal sensation [18] and thirst [14], and improved thermal comfort [9] when exposed to the oral cavity.…”

“…Menthol mouth swilling is considered a practical ergogenic strategy before and during exercise in hot environments [11,30] and has been used to improve performance during time trials [17,18] and time to exhaustion [16,31]. Perception of menthol mouth swill concentration may be highly individual in nature, with 200 gene variants of the receptor responsible for menthol detection (TRPM8 [32]).…”

“…All menthol-containing studies [9,10,[16][17][18][19]31] have employed a repeated exposure during the exercise bout-this is quantified via time or distance. Better understanding the time course of menthol mouth swilling responses, and the potential impact of concentrations upon these, would provide insight into possible limitations in application for menthol-containing strategies.…”

“…All solutions were colourless/transparent. Participants swilled 25 mL of menthol solution for 10 s [16]. They were then asked to rate the solution for Smell, Taste, Mouth Feel, Freshness & Irritation, using 15 cm Visual Analogue Scales (VAS).…”

“…A more contemporary application of menthol has been that of an ergogenic aid which can be applied topically [15], used as a mouth swill [16][17][18] or ingested alongside ice slurry [9,10,19]. This use is fitting, with menthol shown to increase the drive to breathe [20], elevate ventilation [21] and attenuate thirst [13], along with eliciting sensations of coolness and freshness that may alleviate thermal symptoms during exercise [3].…”