The Badwater 135 just finished. For those of you not familiar with Badwater 135, it is one of the most difficult ultra races because it traverses Death Valley, where temperatures were reported at 40 C. Both of the 1st-place winners for the men and women broke previous records (Turner, 2026) . It is a testament to the body’s ability to adapt to extreme heat. For most of us, we won’t be subjecting ourselves to these extremes, but with summer in full swing, most of us will be dealing with hot and, depending on where you live, humid conditions. Exercising in the heat can be challenging for anyone, from elite athletes to regular folks just trying to stay healthy.
It is important to understand the impact heat has on the body when you are exerting yourself. As you exercise, your body produces heat, and depending on the type and duration, the range can be anywhere from 0.5 °C to 1.5 °C. Your body is constantly working to maintain homeostasis, keeping things on an even keel. So as your core temperature increases, your body begins to do its job. Your heart rate increases, and blood is shifted away from your internal organs to your skin, and you begin to sweat. All of this helps cool your body in “normal” conditions. When you add increased ambient temperature, anything above 26.6 °C to the equation, your body now has more to compensate for (Damatto et al., 2019).
You can adapt to exercising in hot weather, and the participants in Badwater are a testament to the body’s ability to adjust. What the research tells us is that your body can learn to adapt to an increase in ambient temperature, and for most, it takes about 7-14 days. What you will find is that as your body adapts, your core temperature and heart rate at rest will lower, and during exercise, your core temperature will increase along with an increased sweat rate, but your heart rate will also decrease. The decrease in heart rate is considered to be a good thing and is a sign that your body is beginning to acclimate to exercising in higher temperatures. The reason for the change is related to an increase in plasma volume and an improved cardiac output (how much blood your heart can pump out in a minute (Brown et al., 2022).
The process for acclimating your body to heat should be done in steps. Gradually increase the amount of time and intensity over the 7-14 days. The goal is to help your body learn. Sweating is one of the key ways your body cools itself. The evaporation of sweat from the surface of your body helps to cool the circulating blood (Rosales et al., 2025). As you acclimate to the heat, your body should begin to sweat at a quicker rate; your core temperature will lower during and post-exercise, along with your heart rate, all signs that you are getting used to the heat . Age is also a factor; at around age 65, and even beginning at age 40, our sweat rate can decrease, likely due to changes in cardiorespiratory fitness, as seen in a decline in VO2 Max (Deshayes et al., 2026). Research does suggest that well-trained older runners can still perform in higher temperatures, though the heat may have some negative impact on cognition (Deshayes et al., 2026). Sex may also be a factor; though there are fewer studies on female athletes, the main difference is that women do not experience the same increase in Plasma Volume (Rosales et al., 2025; Kelly et al., 2023).
The current protocol for acclimation is to exercise at 60% of your VO2 Max and increase the time from 48 minutes to 80 minutes depending on your goals (Racinais et al., 2015). It comes down to slow and steady exposure. Hydration and fueling are also critical components of acclimation. With increased sweating, you will have a higher risk of dehydration. Hydrating pre-workout, during and post-workout, along with supplemental electrolytes during your run, are critical to preventing dehydration. The research is still out on how much fuel you should be using, but some studies show that your body uses more glycogen in hot conditions (Alabdulwhahed et al., 2022). You should be fueling both during and after exercise, and the rule of thumb is anything over 90 minutes requires in-session fueling.
Even though we are in the middle of the hottest months here in the United States, you can still train. You need to be cautious. If you feel unwell, dizzy, lightheaded, nauseated, confused, have muscle cramps or stop sweating, you need to stop and cool down. If you are out running alone, you should make sure that someone knows where and how long you anticipate being out for your run. Many sports watches and apps can track where you are, so if you need assistance, they will pinpoint your location. There is nothing wrong with stopping and cooling off or getting some help. The old saying better safe than sorry is certainly a good one.
References
Alabdulwahed, S., Galán-López, N., Hill, T., James, L. J., Chrismas, B. C., Racinais, S., Stellingwerff, T., Leal, D. V., Hausen, M., Chamari, K., Fullagar, H. H. K., Esh, C., & Taylor, L. (2022). Heat adaptation and nutrition practices: Athlete and practitioner knowledge and use. International Journal of Sports Physiology and Performance, 17(7), 1011–1024. https://doi.org/10.1123/ijspp.2021-0462
Blackman, C., Bellenger, C., Périard, J., Wakim, D., & Chalmers, S. (2026). Thermophysiological response of adults to long-distance running in different ACSM Environmental Risk Conditions: A systematic review and meta-analysis. Journal of Sport and Health Science, 101158. https://doi.org/10.1016/j.jshs.2026.101158
Brown, H. A., Topham, T. H., Clark, B., Smallcombe, J. W., Flouris, A. D., Ioannou, L. G., Telford, R. D., Jay, O., & Périard, J. D. (2022). Seasonal heat acclimatisation in healthy adults: A systematic review. Sports Medicine, 52(9), 2111–2128. https://doi.org/10.1007/s40279-022-01677-0
Damatto, R. L., Cezar, M. D., & Santos, P. P. (2019). Control of body temperature during physical exercise. Arquivos Brasileiros de Cardiologia. https://doi.org/10.5935/abc.20190081
Deshayes, T. A., Barry, H., Dahhak, A., Sodabi, D. G., Oubouchou, K., Hsouna, H., Debray, A., Desrosiers‐Gagnon, C., Chaseling, G. K., Gendron, P., & Gagnon, D. (2026). Heat acclimation improves the neural control of body temperature during heat stress in older adults. The Journal of Physiology, 604(12), 4968–4983. https://doi.org/10.1113/jp290417
Heatherly, A. J., Caputo, J. L., Johnson, S. L., & Fuller, D. K. (2023). Heat acclimation knowledge among recreational runners. Sports, 11(2), 49. https://doi.org/10.3390/sports11020049
Kelly, M. K., Bowe, S. J., Jardine, W. T., Condo, D., Guy, J. H., Snow, R. J., & Carr, A. J. (2023). Heat adaptation for females: A systematic review and meta-analysis of physiological adaptations and exercise performance in the heat. Sports Medicine, 53(7), 1395–1421. https://doi.org/10.1007/s40279-023-01831-2
Racinais, S., Alonso, J.-M., Coutts, A. J., Flouris, A. D., Girard, O., González-Alonso, J., Hausswirth, C., Jay, O., Lee, J. K., Mitchell, N., Nassis, G. P., Nybo, L., Pluim, B. M., Roelands, B., Sawka, M. N., Wingo, J., & Périard, J. D. (2015). Consensus recommendations on training and competing in the heat. Sports Medicine, 45(7), 925–938. https://doi.org/10.1007/s40279-015-0343-6
Rosales, A. M., Ruby, B. C., & Slivka, D. R. (2025). The impact of sex and heat exposure schedule on heat acclimation. Medicine & Science in Sports & Exercise, 57(10S), 362–363. https://doi.org/10.1249/01.mss.0001157688.29542.23
Turner, J. (2025, July 29). Badwater 135 results 2026: Records shattered in “World’s toughest footrace” | Ultramarathon News | RUN247. https://run247.com/running-news/ultramarathon-news/badwater-135-2026-results-report
Leave a Reply