It's Getting Hot in Here: Tips for Acclimating to Running in the Heat

Here in Atlanta, temps have been rising since the end of March, and you may have noticed that some of your runs have felt more challenging despite no change in terrain or pace. You're not imagining things! Temperatures over 77 degrees Fahrenheit negatively impacts performance for running distances over 800m.

Heat acclimation is the process where, by exercising in the heat repeatedly, your body makes adaptations to improve tolerance to activity in hotter temps which can improve safety and performance. These adaptations generally occur after ~ 10 exposures to exercising in the heat, which could mean 10 days if exercising in heat daily, or closer to 30 days if exercising every third day. (1,2)

After a few days of exposure to warmer temperatures, your body begins to make physiologic changes to allow for better tolerance to the heat. Your body begins to sweat at lower core temperatures and dilates blood vessels at the skin earlier into exercise to allow better evaporative cooling to keep your body temperature lower. Your blood plasma volume also increases, which increases the amount of blood circulated with each heartbeat, keeping your heart rate lower both at rest and with exercise. The sweat you lose is less salty, which preserves electrolytes. (1) Altogether these changes result in you feeling less hot and less strained when exercising in hotter conditions!

Pyor et al., 2018

Our bodies are amazing and can adapt well to changes in weather, but it does take time. Initially, heat's stress on the body increases the overall difficulty of exercise, and you may need to decrease intensity - for runners, slowing down pace - to accommodate for this. It may be better to use rate of perceived exertion (RPE) instead of specific pace goals for the first few days of heat exposure, to avoid adverse heat related effects.

It's also important to support your body in warmer conditions. In addition to consuming extra fluids to support increased sweat loss and prevent dehydration, your body also needs more carbohydrates, as your body utilizes more carbs when performing endurance exercise under hot conditions. (3) Increased stress on the body from exercising in the heat may also require more, or different, recovery. It's important to listen to your body's cues as you navigate training into a new season. You can also aim to run early in the morning or in the evening to avoid the hottest temperatures of the day, which can be the most difficult and dangerous to exercise in, and select light colored, breathable fabrics to exercise in.

If you're feeling the heat, be patient! It is repeated exercise in the warmer weather, while using common sense heat safety precautions, that will teach your body to make appropriate adaptations to ease the difficulty of running in the heat. Before you know it, you'll be running comfortably, albeit a bit sweatier!

Happy Running, and Stay Hydrated!

Dr. Elizabeth Karr PT, DPT, OCS

Precision Performance and Physical Therapy, Atlanta's Running Clinic

References:

1. Pryor JL, Johnson EC, Roberts WO, Pryor RR. Application of evidence-based recommendations for heat acclimation: Individual and team sport perspectives. Temperature (Austin). 2018;6(1):37-49. Published 2018 Oct 13. doi:10.1080/23328940.2018.1516537

2. Périard, J.D., Racinais, S. and Sawka, M.N. (2015), Adaptations and mechanisms of heat acclimation. Scand J Med Sci Sports, 25: 20-38. https://doi.org/10.1111/sms.12408

3. Mougin L, Macrae HZ, Taylor L, James LJ, Mears SA. The Effect of Heat Stress and Dehydration on Carbohydrate Use During Endurance Exercise: A Systematic Review and Meta-Analysis. Sports Med. 2025;55(11):2825-2847. doi:10.1007/s40279-025-02294-3