Why did so many athlete’s preparing for the Paris 2024 Olympics choose “heat camps” over altitude? Tadej Pogacar, the 2024 Tour de France Champion, said the CORE sensor helps him with pacing (1).
What’s all the fuss about heat training, and could it benefit you when preparing for your next event?
The Physiology
Similar to altitude, heat training can boost your hematocrit (red blood cell, RBC) count, which will result in better oxygen carrying capacity. This is due to the loss of blood plasma volume via heavy sweating and the following physiological compensation, where both the plasma volume expands and more RBCs are being produced to maintain the blood homeostasis.
Studies show that heat training improves thermal comfort and reduces physiological strain, and enhances aerobic exercise performance in heat. However, it is suggested that exercise performance may also improve in temperate (mild) environmental conditions as a result of heat training (2-4). The intensity, duration, and frequency of heat training greatly dictate the extent of the adaptations (5-8). Other biological adaptations to heat training include improved fluid-electrolyte balance, which might be one of the key adaptations for improved exercise performance; lowered heart rate and metabolic responses, and improved ability of the body to cool off (5-8). Adaptations typically take place after repeated exercise-heat exposures are sufficiently stressful to invoke heavy sweating and an elevated whole-body temperature - for at least 1-2 weeks of about 90 minutes heat exposure per day (9,10).
Without appropriate heat training exposure, even the fittest athletes will experience decrements in performance due to cardiac drift (gradually increasing heart rate despite no changes in work rate); decreasing power output and absorption of fuel.
Heat Training - How to?
Heat training sessions can be done as standalone or attached to longer training sessions.
Even a few weeks of focused heat training can boost aerobic efficiency and improve blood plasma levels (and thus, RBC count) similar to altitude exposure. The quickest way to gains is by doing heat training every day or every other day, but 2-3 sessions per week over 2-6 weeks is sufficient to gradually build adaptations (11). Heat training sessions can be performed both indoors and outdoors, but may be more practical indoors when it is easier to control the temperature and relative humidity, and there will be no windflow. It will also be easier to control the exercise intensity when using the indoor trainer for bike or treadmill for running.
Example 1: Heat training as a part of longer training session
Preserve the last 30-50 min of a longer bike ride or run for heat training. You can perform the first, “normal” part of the session inside or outside, but the last, “heat training” part should be performed inside with no air condition/cooling and with extra layers, if possible. The heat training part does not need to be intense. Usually it will feel more uncomfortable by default due to the lack of cooling.
Example 2: Heat training as a standalone session
Similar to the previous, the standalone heat training sessions should be done indoors, without airco/cooling. More clothing may or may not be necessary depending on the room temperature. You should perform 60-90 min of steady, aerobic work while monitoring your core body temperature (if possible).
In both cases, it is typically recommended to stay within the “optimal heat training zone” that is typically below 39 degrees Celsius. No extra benefit comes from going beyond that zone, and higher temperatures can cause greater heat strain to the body, which can be dangerous and delay recovery and the desired adaptations. Typically, staying in the right zone requires tapering off the power/speed.
The CORE sensor provides an easy way of measuring and monitoring body temperature via its small size and connectivity with several sport watches and cycling head units. At the moment, CORE is the only non-invasive wearable for continuous core body temperature monitoring that is available to the public (11). CORE is now offering a new heat adaptation score to help you to better understand your current heat adaptation status and ability to perform in the warm conditions. If a session has an adequate Heat Training Load your Heat Adaptation Score will increase, whereas if no Heat Training Load is present the score will decline. CORE recommends doing heat training sessions at an intensity where the Heat Strain Index is between 3.0–6.9 (12).
References
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Cotton, J. Pacing Pogačar, Boosting Evenepoel: How Heat Training Became the Peloton’s Hottest Performance Enhancer. Velo. https://velo.outsideonline.com/road/road-training/pacing-pogacar-how-heat-training-is-boosting-pro-cycling/
- Kirby, N. V., Lucas, S. J. E., Armstrong, O. J., Weaver, S. R., & Lucas, R. A. I. (2021). Intermittent post-exercise sauna bathing improves markers of exercise capacity in hot and temperate conditions in trained middle-distance runners. Eur J Appl Physiol 121(2), 621–635.
- Scoon, G. S., Hopkins, W. G., Mayhew, S., & Cotter, J. D. (2007). Effect of post-exercise sauna bathing on the endurance performance of competitive male runners. Journal of science and medicine in sport, 10(4), 259–262.
- Minson, C. T., & Cotter, J. D. (2016). CrossTalk proposal: Heat acclimatization does improve performance in a cool condition. The Journal of physiology, 594(2), 241–243
- Taylor N. A. (2014). Human heat adaptation. Comprehensive Physiology, 4(1), 325–365.
- Sawka, M.N., Périard, J.D., and Racinais, S. (2016). Heat Acclimatization to Improve Athletic Performance in Warm-Hot Environments. Gatorade Sports Science Institute. https://www.gssiweb.org/sports-science-exchange/article/sse-153-heat-acclimatization-to-improve-athletic-performance-in-warm-hot-environments
- Périard, J.D., S. Racinais, and M.N. Sawka (2015). Adaptation and mechanisms of human heat acclimation. Scand. J. Med. Sci. Sports. 25:S20-S38.
- Sawka, M.N., S.N. Cheuvront, and M.A. Kolka (2003). Human adaptations to heat stress. In: H. Nose, G.W. Mack and K. Imaizumi (eds.) Exercise, Nutrition and Environmental Stress, Traverse City, MI: Cooper Publishing, 3:129-153.
- Hough, P. (n.d.). Heat Acclimation Training. St. Mary’s University Sport and Exercise Physiology Blogs. https://www.stmarys.ac.uk/blog/physiology/heat-acclimation-training.aspx
- Sawka, M.N., Périard, J.D., and Racinais, S. (2016). Heat Acclimatization to Improve Athletic Performance in Warm-Hot Environments. Gatorade Sports Science Institute. https://www.gssiweb.org/sports-science-exchange/article/sse-153-heat-acclimatization-to-improve-athletic-performance-in-warm-hot-environments
- N.p. Basics of Heat Training. CORE. https://corebodytemp.com/pages/basics-of-heat-training
- N.p. How to do a Heat Session. CORE. https://corebodytemp.com/pages/how-to-do-a-heat-session%20
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Learn more on Core Sensor! Plus, check out these essential tools for heat training: the Core Suit for indoor heat sessions, the Nix Hydration Biosensor, and Precision Hydration Products.