Mint Performance: how to beat the heat with menthol!

We wanted to share some recent and fascinating research on how menthol could help athletes beat the heat – and combat the cold!

Menthol is cool

Menthol possesses the ability to chemically trigger the cold-sensitive receptors in the skin, which produces well-known cooling sensation  when menthol is inhaled, eaten, or applied to the skin.

This ‘cooling’ action of menthol has recently provoked interest in its use as a potential performance booster for athletes competing in the heat. The theory is that if menthol can reduce the perception of heat, athletes using menthol might be able to reduce their levels of thermal discomfort when exercising in hot condition (higher levels of thermal discomfort are known to impair exercise performance). However, a counter argument against menthol is that by encouraging athletes to exercise harder in hot conditions, menthol use could increase the risk of heat illness – because athletes will be less aware of the signs and symptoms of overheating.

The Evidence

A fairly recent British study sought to shed light on this by answering two questions (1):

1) Does menthol use in the heat really relieve thermal discomfort?
2) Does menthol use in the heat lead to a rise in core temperature, putting athletes at risk of heat illness?

In this study, eight male participants completed two trials in hot conditions (33.5 °C, 33% relative humidity) where their t-shirt was sprayed with a control spray (water) or a menthol spray 10kms into a 16km cycling time trial (ie when they were hot and uncomfortable). The key finding was that compared to water, a menthol spray didn’t affect the time trial performance but it DID made participants feel cooler and more comfortable, resulting in lower perceived less exertion. Moreover, the core temperatures of the cyclists rose equally in both the water and menthol conditions – ie there was no evidence that menthol use put the cyclists at any additional risk of heat stress/illness.

Menthol vs. Ice

The following year (2016), a team of Aussie and British scientists carried another study on menthol use in hot conditions(2). What they investigated was whether merely reducing the sensation of thermal discomfort by using a menthol mouth rinse was in any way comparable in terms of performance to reducing actual thermal load by consuming a pre-exercise ice slurry drink (a technique known to reduce core temperature.

To test this, 11 moderately trained male runners each completed three trials consisting of 5km runs on a non-motorised treadmill in hot conditions (33°C) on three separate occasions. However, the trials varied as follows:

  • In one trial, they consumed an ice slurry ingestion before the trial.
  • In another trial, they used a menthol mouth rinse during the trial.
  • In a third trial, they consumed nothing before or during the trial (control).

The researchers recorded the runners’ core temperatures in each trial and also compared the times recorded. The main finding was that compared to the ice slurry and control trials, the runners’ average times were significantly faster when using the menthol mouth rinse (25.3 minutes in the menthol trial, 26.3 minutes in the ice slurry trial and 26.0 minutes in the control trial). This was despite the fact that the ice slurry helped keep the runner’s core temperatures down whereas the menthol mouth wash didn’t).

The most likely explanation is that the menthol rinse significantly decreased the amount of perceived thermal sensation (how hot and uncomfortable the runners felt), especially between 4 and 5kms. This reduced thermal sensation almost certainly helped ‘trick’ the brain into believing effort levels were lower, allowing the runners to run faster! The ice slurry meanwhile didn’t reduce thermal sensation, even though it did actually reduce core temperatures.

Although this might seem rather bizarre, there’s good evidence for the rationale as a large body of recent research has established that your physical performance is profoundly influenced by not only the body’s physiology and biochemistry during exercise, but also how the brain perceives that exercise/effort. This explains why uplifting music can suddenly boost your energy levels halfway during a bout of exercise – even though nothing has changed physiologically!

Practical implications

The evidence for the benefits of menthol use in hot and cool conditions is very persuasive. By reducing the sensation of thermal discomfort, the same workload performed in hot conditions is likely to feel easier in hot conditions. If the duration of exercise is longer, it may also help improve performance by delaying the onset of fatigue. Both menthol skin sprays and drinks containing menthol are likely to be effective.

However, some caution is required; by potentially blunting sweat volumes, prolonged menthol use may not be advisable in very hot conditions and when access to adequate fluid consumption is difficult. 

This is an op-ed article & not necessarily the views / beliefs of BFUNCTIONAL.

References

  1. Scand J Med Sci Sports. 2015 Jun;25 Suppl 1:211-8. doi: 10.1111/sms.12395
  2. Scand J Med Sci Sports. 2016 Oct;26(10):1209-16
  3. Int J Sports Physiol Perform. 2019 May 1;14(5):644-649
  4. J Sci Med Sport. 2019 Jun;22(6):707-715.
  5. Scand J Med Sci Sports. 2017 Dec;27(12):1560-1568
  6. Scand J Med Sci Sports. 2018 Mar;28(3):1193-1200
  7. Peak Performance: 2019; May.