I’m sitting here sweating. The Bow valley is in the midst of a heat wave at the time of this writing. I rode my bike to Banff this afternoon and the Legacy trail was quiet, unbelievable for a beautiful Sunday at the end of June. I assume that the soaring temperatures were putting people off, and this got me thinking about exercise in the heat. This weekend a 100 mile footrace took place in California - the Western States 100. Temperatures during the race regularly top 40 Celsius, and this weekend was no exception. I ran this race in 2016 and I can attest to the challenges with this kind of heat! The Tokyo Olympics are scheduled for 2022, and temperatures are expected to top 31 Celsius, with 70% relative humidity. It’s being billed as one of the ‘hottest feeling’ Olympics ever. Athletes, their coaches and physiologists of course are well aware of this, and will be employing various heat acclimation strategies in the lead up to these races.
Athletes who are looking to compete in hot environments often utilize various dry sauna protocols, hot water immersion techniques, and various other decidedly unpleasant strategies to force their bodies and their minds to adapt! When we are suddenly exposed to extreme heat, and especially if we are trying to exercise in it, a number of immediate physiological effects take place that make us feel sluggish and off our A game. Whilst we may feel terrible, under the hood our bodies are working hard to minimize any chance of overheating. Our bodily processes are most efficient at very specific temperatures, and unless that internal ‘core’ temperature is maintained in a very tight range, things can go awry.
You may notice during your first hot run or ride, that things feel much harder than they should. Your heart rate is higher than it should be, you sweat profusely, you are more easily out of breath, and, well, everything just feels harder. After a few more sessions though, everything starts to feel easier. Our perceived level of exertion for a given activity, begins to normalize. Some of this is due to physiological adaptation, or heat acclimatization, and I am not going to discuss the myriad of things that occur during physiological acclimatisation here; some of this improvement however is primarily psychological, and recent research has looked at how our perception of heat can be changed, to make exercise in the heat just feel easier.
One recent topic that caught my eye, and which has been garnering interest in the scientific community for a few years, is the use of menthol to reduce our perception of heat stress. We have all experienced that cooling sensation when we suck on a minty, menthol candy. Well it turns out that this strategy may have some potential performance enhancing effects, and most of this effect seems to be in our heads!
When we consume menthol and other substances, specific receptors located on heat sensitive nerves in our mouths, called TRP (transient receptor potential) channels, are stimulated. The receptor activated by menthol, TRPM8, evokes a cooling sensation in the mouth when triggered. Cayenne pepper and wasabi paste stimulate other TRP channels, with less pleasant effects in the mouth, but it’s the same idea. We also have TRPM8 channels in the skin, and applying a menthol based cream also produces a cooling sensation. When athletes were asked gargle or ingest a weak menthol solution during exercise, or when a menthol cream was applied, the apparent perception of exertion, and the sensation of heat stress, both diminished.
Investigators have looked at whether this diminished sensation of overheating could in fact improve performance in the heat and, guess what, it seems to work! In one trial, scientists had runners perform a 5km time trial in 33 celsius conditions on a treadmill. Personally, I could think of nothing worse than this, especially as a rectal thermometer was used to monitor core temperatures. The time trials were completed under three different test conditions. In one trial, the runners consumed an ice slurry drink before the run. This approach has been shown to lower core temperature transiently, which we know improves hot weather performance, and is widely used. In another of the time trails, our runners used a menthol mouth rinse during the run, and in the third trial they consumed nothing before or during the run. Core temperatures were monitored in all three time trials. The results were interesting.
Not surprisingly, only the ice slurry helped keep the runners’ core temperatures down. Menthol ingestion had no effect on core temperature, and the results were identical to the ‘no treatment’ control group. Somewhat surprisingly, however, the times for the 5km run were significantly better when menthol was ingested than in either of the other two scenarios. Menthol allowed the athletes to run faster, without any discernible effect on core temperature. There were no apparent physiological changes. The effect seemed to be psychological, and the subjects noted that they felt cooler. Other studies have been able to reproduce these results, and have even shown that menthol can extend the ‘time to exhaustion’ in longer efforts.
The conclusion is that menthol has the potential to reduce the sensation of overheating, essentially tricking the brain into thinking that it’s cooler than it is, allowing us to push harder. It’s the brain, ultimately, that determines how hard we can push when things become unpleasant, acting as a ‘Central Governor’ that slows us down when our core temperature begins to rise, preserving our internal processes and keeping us alive. Trick the brain into thinking that we are cooler than we are, and we shouldn’t slow down as much.
There are a few caveats of course, as with all scientific work. These results may not be generalizable to all sports, and a lot more work needs to be done to ensure that the practice is safe and applicable! It’s been suggested that the use of menthol could potentially lead to overheating, a very dangerous situation, and some people are intolerant, so I would hesitate to recommend this as widespread practice at this point. For now, however, I think it’s safe to say that we are going to see various menthol strategies being used in hot weather events going forwards. Enjoy those candies!