Menthol protects runners and cyclists against hot weather
It probably doesn't matter whether you use a homemade sports drink with menthol dissolved in it or gelatin capsules you suck on. The point is to keep menthol in your mouth while doing continuous intensive exercise. And whether you're a runner or cyclist, it'll help you to perform better, write Australian sports scientists, working at the University of Newcastle, in an article in the Scandinavian Journal of Medicine & Science in Sports.

The researchers did an experiment with 11 male recreational runners, who, on three different occasions, had to run five kilometres on a treadmill in as short a time as possible. The ambient temperature was 33 degrees Celsius and the humidity was high.On one occasion the men were given a little Gatorade to drink every 15 minutes [Control]. On another occasion the researchers gave the subjects ice slurry at 1 degree Celsius. The idea behind this was that the slurry would reduce the subjects' body temperature and thus help enhance performance.
On the third occasion the men were given ordinary Gatorade, but every other kilometre they were given fluid in which menthol had been dissolved. They kept this in their mouth for 5 seconds before spitting it out. They spat it out for methodological reasons. Menthol may also be an interesting supplement for endurance athletes, and the researchers wanted to exclude this factor. They were only interested in the cooling effect of taste sensation of menthol.
When the subjects had no ice slurry and no menthol they covered the five kilometres in an average of 26 minutes. When they drank ice slurry it took them 26.3 minutes to cover the distance. So statistically the slurry had neither a positive nor a negative effect on the men's times.

The menthol mouthwash on the other hand did have a statistically significant effect. When the men were given menthol they covered the five kilometres in 25.3 minutes.
Control = CON, circles; ice slurry = ICE, squares; menthol = MEN, triangles.

The figure above shows that the performance-enhancing effect of menthol became visible at the halfway point and during the last part of the run.The ice slurry prevented the athletes' temperature from rising; the menthol did not do that. The ice slurry and the menthol had no effect on the men's heart rate.
The researchers suspect that menthol in the athletes' mouth caused a cooling sensation. As a result of this, the athletes were involuntarily able to run a little faster. At the end of the 5-km run during which the athletes had been given menthol, their blood also contained more prolactin than it did at the end of the other sessions. Prolactin is a hormone that is released, among other things, after physical exertion.

"Athletes should consider the use of menthol during competition and industry should consider the addition of menthol to hydration and nutritional sports products", the researchers concluded.

Scand J Med Sci Sports. 2016 Oct;26(10):1209-16.