Wednesday, October 21, 2009

Menthol: Fresh Breath and Better Performance?

Exercising in the heat is always a difficult task. Hot environments place a tremendous demand on the cardiovascular and thermoregulatory systems. This typically leads to decreased performance, particularly in sports that last an hour or more. As a result, coaches and players are always searching for new ways to perform in the heat. In a new study, researchers at Manchester Metropolitan University in the United Kingdom report that simply rinsing the mouth with menthol, a common flavoring agent, can actually improve performance during exercise in a hot environment.

The researchers asked nine moderately trained subjects to exercise on a stationary bicycle at ~65% of their maximal capacity. They were told to continue exercising as long as possible while the total duration was recorded. On one occasion, subjects swilled a 0.01% menthol solution in their mouth for 10 seconds after which it was spit out without swallowing. On the other occasion, they swilled an orange flavored placebo drink. They were given the solution every 10 minutes and were allowed to drink as much water as they wanted. All of the bouts were performed in the heat at a room temperature of 34°C or 93°F.

Eight of the nine subjects improved their exercise duration when they swilled the menthol. Total exercise time increased from an average of 58 to 63 minutes. Despite this improvement in performance, there were no differences in the subjects’ body temperature or the amount of energy expended. What seemed to be improved was the perception of their effort. Overall, the subjects felt that that the menthol was “refreshing” and “stimulating”. This resulted in the subjects feeling a reduced sense of effort during the exercise bout, particularly a reduced effort of breathing. That is, breathing felt easier which made the exercise seem easier.

The authors conclude that the improvement in performance was probably due to psychological factors. The menthol may have stimulated some region of the mouth which activated a network of taste- and reward-regions of the brain. The pleasantness of a cool mouth coupled with taste and flavor may have caused the subjects to experience less discomfort as they were approaching exhaustion.

Menthol is an interesting compound. It comes from various mint oils as well as peppermint. When it is applied to the skin, there is a cooling sensation. The same sensation is experienced when taken orally. As a result, many companies include menthol in all sorts of skin creams, foods, mouthwashes, medications and cigarettes. Ben Gay ointment, peppermint candies, and many throat lozenges all contain menthol. Some people report that this cooling effect increases alertness and reduces minor pain. For example, a throat lozenge soothing sore throat pain. So it is not surprising that swilling a menthol drink might reduce one’s perception of breathing during exercise.

There are a few important points to be made about this study. First, and most importantly, the menthol did not actually lower body temperature. The improvement in performance does not indicate that menthol protects against any of the potential problems of exercising in the heat such as dehydration. It remains very important that when exercising in the heat, players drink plenty of fluids and to be aware of heat-related illness and injury.

Second, the type of exercise performed in this study doesn’t really simulate match play. The subjects were asked to exercise at a constant, pre-determined pace and to continue as long as possible. Match play requires players to start and stop and run at a variety of speeds. This means that the reduced perceived exertion caused by the menthol may be specific to the type of exercise studied and may not occur during an activity like soccer. Also, it is difficult, if not impossible for players to drink every 10 minutes during a match.

Despite these drawbacks, the finding that menthol may improve performance is intriguing. While it may not actually combat the physiological effects of exercising in the heat, including it in drinks may have some positive psychological effect. This study also adds to a growing body of research showing that what goes into your mouth may affect exercise. Earlier, the SSO reported that merely swilling a carbohydrate beverage (sports drink) might also affect the central nervous system and improve performance (LINK). These studies suggest that the mouth may be more important than previously thought. It may be more than a simple a passage way to the stomach but a key sensory component of perceived exertion.

Reference:

Mundel T, Jones DA (2009) The effects of swilling an L(-)-menthol solution during exercise in the heat. European Journal of Applied Physiology, DOI: 10.1007/s00421-009-1180-0