Heat acclimatisation
Heat acclimatisation - is it as simple as taking a bath?
The human body is extremely good at doing the bare minimum to preserve resources. This is why doing something once, or sporadically, has little impact. Lift weights at the gym 6 times over a year and you’re looking at no change. Lift weights 6 times in 2 weeks and your body will respond by making you better at lifting weights. Once it’s convinced that it’s worth expending resources it will make the necessary changes. It makes very specific changes to make the specific activity easier. As anyone who has had gaps in their training will know only too well, when you stop doing an activity the body will gradually stop providing the resources that keep it in the best shape for that activity.
We know that consistency matters, and specificity too. But specificity is actually not so black and white; take the example of Jim Walmsley running insanely fast 100 milers off of bike training, or a season of cross country skiing.
So when does specificity matter, and why does it sometimes not seem to, and what has this got to do with heat acclimatisation?
To prepare the body for a task - a trail race or ultra marathon for example - we must get it to make all the changes that we need for the race. In some ways it doesn’t matter how we get it to make those changes, so long as it does make them.
When we look at acclimatisation we can think about what physiological changes we need and work backwards.
For heat we need:
to lower the point at which the body starts to sweat and cool itself;
to increase sweat rate (with lowered sodium in sweat);
to increase blood plasma volume and red blood cell volume;
to change perceived effort in heat.
Previous interventions attempted to simulate heat whilst running. This often meant wearing more clothing, even bin bags. But this might actually be counterproductive if it reduces the quality of the run session. More recent research has looked at supplementing running with indoor biking in a hot room and most interestingly hot baths or saunas post-exercise.
Just get in a hot bath after running…
We can achieve all of the necessary adaptations with post-exercise heat stress (bath / sauna). This is highly desirable as it requires no special equipment (beyond a bath) and allows the athlete to continue quality training.
One research study found that 6 days of post-exercise hot water immersion (40 minutes at 40°C) is effective (in men). As the body tends to respond to anything if we are persistent (consistency trumps all) it is likely that this could be spread over 2-3 weeks (i.e. 2-3 times a week) and still get the same effect at the end of it. We should remember that the body will revert back without continued stimulus but avoid adding too much new stress in the taper.
If you have a race in the heat you can prepare yourself at home. 20 minutes in a hot bath 6-8 times over 2-3 weeks is likely sufficient.
Of course, be mindful of not doing anything that makes you feel unwell, or dizzy. You can always start at lower temperatures and for shorter time periods.
References
Zurawlew, M.J., Walsh, N.P., Fortes, M.B. and Potter, C. (2016), Post-exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat. Scand J Med Sci Sports, 26: 745-754. https://doi.org/10.1111/sms.12638
Oberholzer Laura, Siebenmann Christoph, Mikkelsen C. Jacob, Junge Nicklas, Piil Jacob F., Morris Nathan B., Goetze Jens P., Meinild Lundby Anne-Kristine, Nybo Lars, Lundby Carsten (2019) Hematological Adaptations to Prolonged Heat Acclimation in Endurance-Trained Males, Frontiers in Physiology, 10. doi: https://doi.org/10.3389/fphys.2019.01379
Saunders, Philo U., Garvican-Lewis, Laura A., Chapman, Robert F., Périard , Julien D., Special Environments: Altitude and Heat International Journal of Sport Nutrition and Exercise Metabolism, 2019, 29, 210-219. https://doi.org/10.1123/ijsnem.2018-0256