Tips for Exercise in the Heat
As we enter the dog days of summer, I’ve been asked by multiple clients for tips on how to deal with the heat. The unfortunate news is- no matter who you are, the heat will negatively impact your performance. I can however offer a few tips on how to minimize the negative effects, as well as a few nutritional advices in hopes of preventing dehydration in a hot environment.
If you monitor your exercise intensity via heart rate: know that in a hot environment, your heart rate will be elevated significantly compared to a cooler environment. If your heart rate is normally around 150 bpm while running an 8:00/mile, when it’s hot out, and running the same pace, your heart rate may be 165 -170 bpm. This tends to be more significant in females, but males will also see some increase in heart rate. This doesn’t mean that you’re suddenly out of shape. It means that your body is trying to complete two major tasks: maintain your exercise intensity, and get rid of heat. Our perception of exertion is also significantly higher in a hot environment. If running an 8:00/mile is moderately challenging on a normal day, in a hot environment, it might seem significantly harder. The more overheated or dehydrated you become, the more significant your increase in heart rate and perception of work effort will be. Don’t worry, this does NOT mean you are out of shape, it does not mean to throw your training out the window! Don’t panic! If 8:00/mile is your normal running pace, don’t be afraid to slow this down in the heat. Trying to maintain your regular speed in a hot condition (particularly if it is humid) could result in heat illness.
Can we acclimatize to the heat?
A classic study done by Nielsen et al. (1993) showed that heat acclimation can occur in 9-12 days of consecutive exposure to heat. Optimal exercise duration during the acclimatization phase is around 90-100 minutes. Following regular heat exposure, subjects were able to exercise 80 minutes to exhaustion on average compared to 48 minutes leading up to acclimatization! Subjects also showed a lower core temperature and an increased sweat rate following regular heat exposure (which is good!). Adaptations to the heat depend highly on exercise intensity, duration, number of hot exposures and whether the heat is dry or humid.
What if you can’t acclimatize to the heat where you live?
New research supports the concept that heat acclimation may actually occur with a hot water bath as well! Zurawlew (2016) recently reported that a 40 minute hot water bath immediately following exercise had heat acclimatizing properties. 17 males completed six days of hot water bath immersion after exercise, and resulted in significant improvements in endurance performance in a hot environment. Seems like a reasonable idea if you are planning on traveling somewhere warm for a race, but you live someplace cold!
Regardless of who you are (novice or elite, male or female), studies generally report that a hot environment will decrease performance by at least 10-20%. With heat acclimation, you may evade this by about 5-8%, but will still ultimately have some decreases in performance. The traditional recommendations regarding heat acclimation:
100 minutes per day (doing more than this doesn’t induce a faster/ better response)- less than this may require more than 10 days
At the temperature you wish to compete at
At the intensity you wish to compete at
The majority (75-80%) of the adaptation occurs in the first 4-7 days
Nutrition/ Hydration Tips for the Heat:
The key to proper hydration in a hot environment involves increased hydration prior to the exercise bout, increased fluid intake during the exercise, and rehydration immediately following. The major issue in the heat is with such a high sweat rate it is almost impossible to intake enough fluid during exercise to prevent some level of dehydration. While drinking water might be good enough under normal circumstances, in the heat, it might be appropriate to also consume some carbohydrates and electrolytes as well. There are many effective brands for carbohydrate beverages and endurance supplements- my recommendation is to try many types, and find out what sits well/ works best for you. Ideal fluid guidelines, which of course can vary from person to person depending on exercise intensity, body size, and environmental conditions:
20 ounces of fluid prior to exercise (1hr)
7-10 ounces of fluid every 20 minutes during prolonged exercise
In a hot humid environment we can lose up to 2-3 L of fluid per hour!!!
Following exercise, consume 16-24 ounces of fluid per every pound lost
Nielsen, B., Hales, J., Strange, S., et al. (1993). Human circulatory and thermoregulatory adaptations with heat acclimation and exercise in a hot, dry environment.
Tatterson, A., Hahn, A., Martini, D., & Febbraio, M. (2000). Effects of heat stress on physiological responses and exercise performance in elite cyclist. Journal of Science and Medicine in Sport 3 (2), 186-193.
Zurawlew, M., Walsh, N., Fortes, M., & Potter, C. (2016). Post exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat. Scandinavian Journal of Medicine & Science in Sports 26 (7), 11.