Menthol mouth rinsing: An applied perspective

By Russ Best, PhD, MSc, CSci

With the Tokyo Olympics rapidly approaching, and increasing global temperatures, applied nutrition practitioners and supporting scientists are looking for ways to physiologically cool their athletes, but the value of perceptual cooling is also gaining a profile; menthol mouth swilling is one such strategy. This article provides a brief synopsis of menthol research to date, followed by a reflection of how we have used menthol mouth rinsing to complement an Ironman™ triathlete’s event nutrition strategy, and concludes by highlighting ethical concerns with menthol mouth rinsing.

Research to date has focused upon endurance sports taking place in hot environments (28 – 35°C) ^1,2, tending to adopt variations on time to exhaustion (TTE) protocols, yet Chris Stevens’ work has shown improvements in time trial performance in runners, over distances as short as 5km ³. Time trial improvements have also been shown in cyclists and triathletes in tropical conditions, when menthol has been combined with other ingested cooling strategies ^4,5. The researched range of time to task completion is ~20 to 70 minutes, with application typically spaced evenly throughout exercise. However, a recent paper by Owen Jeffries showed that a single menthol mouth swill applied at 85% of TTE can extend TTE in the heat, when compared to placebo, and performs as well as ice applied at the same time point ⁶. Here, menthol presents a novel thermal stimulus which challenges the athlete’s interpretation of their perceived thermal state – refreshing athletes and allowing more work to be performed, suggesting that a more tactical approach to the use of menthol may be required.

Currently there is no evidence that menthol benefits intermittent activity ⁷. This may be due to the work rest ratio that typically characterises intermittent sports, or that performance can also be assessed by skill success rates, which have an element of innate variability too. Similarly, menthol may not show performance improvements in events that are comprised of a blend of aerobic and anaerobic work such as a 1500m, especially in tactical races that aren’t limited by thermoregulatory ability per se. Although, strength or power athletes may benefit from the pleasant refreshing sensation of menthol⁸, making the wait time between attempts when competing in the heat more bearable e.g. shot-put or discus. Equally, there may be a unique role for menthol swilling in equestrian sports, especially in Tokyo, as an athlete’s horse also produces a considerable amount of heat, thus imparting another thermal load upon the athlete.

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Author

Russell Best, PhD, MSc, CSci
Centre for Sport Science and Human Performance, Wintec, New Zealand

Originally from North Yorkshire, Russ Best is a Senior Academic Staff Member at Wintec, New Zealand, where he leads the Environmental Ergogenic Strategies and Polo Science research groups, alongside coordinating the Centre for Sport Science and Human Performance MSc programme.

Russell.Best@wintec.ac.nz; @SimplyRussBest

References

1. Stevens CJ, Best R. Menthol: A Fresh Ergogenic Aid for Athletic Performance. Sports Med. 2017;47(6):1035-1042. doi:10.1007/s40279-016-0652-4.
2. Best R, Payton S, Spears I, Riera F, Berger N. Topical and Ingested Cooling Methodologies for Endurance Exercise Performance in the Heat. Sports. 2018;6(1):11-11. doi:10.3390/sports6010011.
3. Stevens CJ, Bennett KJM, Sculley DV, Callister R, Taylor L, Dascombe BJ. A comparison of mixed-method cooling interventions on pre-loaded running performance in the heat. The Journal of Strength & Conditioning Research. June 2016:1-28. doi:10.1519/JSC.0000000000001532.
4. Riera F, Trong TT, Sinnapah S, Hue O. Physical and Perceptual Cooling with Beverages to Increase Cycle Performance in a Tropical Climate. Hayashi N, ed. PLoS ONE. 2014;9(8):e103718–7. doi:10.1371/journal.pone.0103718.
5. Tran Trong T, Riera F, Rinaldi K, Briki W, Hue O. Ingestion of a cold temperature/menthol beverage increases outdoor exercise performance in a hot, humid environment. Romanovsky AA, ed. PLoS ONE. 2015;10(4):e0123815. doi:10.1371/journal.pone.0123815.
6. Jeffries O, Goldsmith M, Waldron M. L-Menthol mouth rinse or ice slurry ingestion during the latter stages of exercise in the heat provide a novel stimulus to enhance performance despite elevation in mean body temperature. European Journal of Applied Physiology. 2018;118(11):2435-2442. doi:10.1007/s00421-018-3970-4.
7. Gibson OR, Wrightson JG, Hayes M. Intermittent sprint performance in the heat is not altered by augmenting thermal perception via L-menthol or capsaicin mouth rinses. European Journal of Applied Physiology. 2018;46(Suppl 1):936–12. doi:10.1007/s00421-018-4055-0.
8. Eccles R, Du-Plessis L, Dommels Y, Wilkinson JE. Cold pleasure. Why we like ice drinks, ice-lollies and ice cream. Appetite. 2013;71:357-360. doi:10.1016/j.appet.2013.09.011.