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Menthol does not (always) improve performance indoors

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It is that time of the year when on the northern hemisphere the temperatures are getting lower and the days shorter. Consequently less and less athletes are training outdoors and most start using the so called turbo trainers on platforms such as TrainerRoad and Zwift. There is no hiding behind the fact that most are not fond of indoor training. It can be boring and very often athletes find it to be harder to put down some serious watts indoors as compared to outdoors. One of the main reasons for this is that thermoregulation indoors is much worse than outdoors.

There is no or very little airflow (unless athletes are using fans) and as a result core temperature rises, athletes start sweating profusely and the perception of effort and heat stress becomes almost unbearable. Up to the point when athletes either give up training indoors or complete it at lower intensities.

Apart from improving air flow using fans and reducing the temperature in the “pain cave” it was proposed that ingestion of a substance called menthol can improve performance due to its “cooling” effect. Menthol – we have all heard about it. When ingested, menthol should induce a feeling of coolness and thus improve the discomfort caused by a high heat stress. There have been quite a few studies on menthol and its effectiveness performed in the past and most showed that menthol can improve performance and/or exercise capacity by improving how people are feeling during exercise in the heat. 

Up-to the point that sports nutrition brands started manufacturing products with menthol. However, in contrast with what studies have utilised to test effectiveness of menthol, these products contain both carbohydrates and menthol rather than only either of these two. Evidence is strong – carbohydrates can improve performance. But the question now is – can menthol improve performance when ingested together with carbohydrates?

This is the question that we tried to answer in our latest study published in the European Journal of Sport Science that we performed at the Human Performance Centre in collaboration with the University of Ljubljana, Faculty of Sports and Jožef Stefan Institute.

Commercially available carbohydrate drink with menthol fails to improve thermal perception or cycling exercise capacity in males

Twelve male participants took part in this study taking place in our laboratory in Ljubljana, Slovenia. During their first visit we determined the boundaries between the exercise intensity domains so that in the subsequent trials participants were exercising either in the moderate or severe intensity exercise domain.

There were two experimental conditions. Study participants on one occasion received a carbohydrate drink without menthol (Placebo) and on the other occasion carbohydrate drink with menthol (Menthol). The order of the trials was counterbalanced so that 6 of the participants first got exposed to menthol and the other 6 initially got a placebo. None of the participants was aware of the study’s aim and were only told that a carbohydrate sports drink is being investigated. In addition to this, both the participants and the researchers were blinded on the order of the trials so that they could not have influenced the results.

During main experimental trials participants were subject to relatively cool environmental conditions (i.e., 20ºC and 30% relative humidity), however there was no air flow as the fans were turned off. Trials consisted of 2 parts. In the first part participants exercised in the moderate intensity exercise domain for 60 minutes during which they received 60g of carbohydrates with or without menthol. This was followed by cycling until task failure in the severe exercise intensity domain.

Results

Contrary to the hypothesis, addition of menthol did not result in longer duration of the exercise bout as seen below.

And neither has menthol influenced the perception of thermal comfort and thermal sensation or rating of perceived exertion.

What does this mean?

Unfortunately we cannot really explain the discrepancy between the results of this and the results of the previous studies. So we are only left to speculate.

One of the attractive speculations is that addition of menthol was ineffective due to presence of carbohydrates. Carbohydrate mouth rinse has been shown to improve performance on its own without carbohydrates ever reaching the bloodstream. The mechanisms are still not completely understood, but it is speculated that there are receptors in the oral cavity sensing the presence of carbohydrates and then signalling the brain that “energy is on its way” and that the athlete “can push harder”. Perhaps menthol on its own affects the same brain centres and when it is combined with carbohydrates there is simply no additive effect.

Definitely more studies are required to elucidate these findings. Despite this, we can clearly say that menthol will not make your indoor training sessions more effective.

You can find the whole study here.

Tim Podlogar

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