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Tips on How to Better Acclimate When Running in the Heat


It’s that time of year again, one day it’s cool and rainy and the next few days it feels like summer, hot and humid. Spring is always a challenging time to race when your body is not acclimated to the warmer temps. You’ve been training all winter in colder weather, then all of a sudden your race next week is thirty 30 degrees warmer! What can you do to better acclimate running in warmer weather? It all starts with planning ahead before your race and understanding more about acclimation.


What is heat acclimatization?

Adaptations to training in the heat depends on the intensity, duration, and frequency of exposure to heat. It takes usually about 7 to 14 days of heat exposure to induce heat acclimatization. In addition, optimal heat acclimatization requires a minimum of daily heat exposure of about 90 minutes combined with aerobic training.


What happens to my body during acclimatization?

During the initial exposure to heat when training, core temps and heart rate are elevated, increasing perceived effort to the training load. Meaning running at race pace will feel a lot harder than when running in cooler temps.


Through daily exposure to heat, improvements in heart rate, skin and core temps, and sweat rate are reached within the first week of exposure. The benefits of heat exposure can retain for about a week but then reduce by about 75% by the 3rd week once the heat exposure ends. So, if you are training in the heat for about a week and then temps reduce again, you may not be acclimated to run in the heat later that month. That’s why spring is always a tough time with training, when the temps go up and down so frequently.


Three classic signs of heat acclimatization include: lower heart rate, lower core temp and higher sweat rate during exercise-heat stress. Sweating may start earlier at a lower core temp after being acclimated. All of these factors improve your cardiac output and training efforts will seem easier.


How can I acclimate to the heat when training in cooler temps?

If you are still training in cooler weather but a week later realize your race is in warmer temps or you chose a race location that is warmer than what you normally trained in, you can actually expose yourself to heat. Home based options include daily exposure to a hot room, hot bath, or sauna. You can even try to simulate training in the heat by running on the treadmill by switching on the heater and humidifier as well.


How can I adjust my hydration when training or racing in the heat?

First of all you need to know your sweat rate. We all know when training in cooler temps sweat rates decrease and once we are training in warmer temps we may need more fluids to prevent dehydration. Test your sweat rate before and after heat acclimatization to determine the amount of fluids and sodium you may need when racing in warmer temps. There are some take home tests, such as Gatorade Sweat Patch, Nix Hydration Biosensor, or through a sweat lab (Precision Nutrition) to determine your sweat rate, but you can also just weigh yourself before and after an hour long run to figure this out as well.


Keep up with your fluids. This means start your race well-hydrated and maintain drinking every 15-20 minutes, 4-8 ounces of fluid, when racing longer than an hour. Electrolytes are key to preventing significant sodium loss in sweat, so consider adding 300-500 mg sodium per hour to your fluids with a small amount of carbohydrate to better help with fluid absorption, especially when sweat rates are high, racing in warmer conditions longer than an hour. You may need anywhere from 16-24 ounces of fluid per hour, so taking small sips every mile can help to prevent dehydration and acclimate to the warmer temps.


What is pre-cooling?

Pre-cooling before your event can reduce core temp and keep you cooler longer during the earlier miles of your race. You can pre-cool by using ice packs in towels placed around your neck, or use fans, cold baths with ice as other options. Also, drinking your electrolyte drink as a slushy can be effective as well.


Staying cool during your race is important as well. I can remember running the Boston marathon in 2012 when temps peaked at 90 degrees, and I was clearly not acclimated to race that day. Sucking on ice chips or popsicles during the race, placing ice in your shirt and under your running hat, using a cold towel wrapped around your neck, wearing a light colored hat and sunglasses are all ways to staying cooler during the race.


How should I adjust my pace when racing in warmer temps?

Lastly, when running in warmer temps and if you are not 100% acclimated to the weather changes, your race pace may need to adjust to be able to run safely and finish the race healthy. Using an adjusted race pace calculator can help to have a plan going into race day. Remember, heat can impact more later in the race, so pacing yourself more conservatively earlier in the race is key no matter how fit you are.


Key Take Home Messages

Adjusting to the heat can be challenging and paces may suffer when you are not acclimated. Remember the following:

  • Acclimatization can take 7-14 days, so plan ahead and try to acclimate if you have the opportunity before race day.

  • Focus on hydration and adding electrolytes based on your sweat rate.

  • Start your race well-hydrated and drink often, every mile, during your race to prevent losing no more than 2% of your body weight.

  • Stay cool by pre-cooling before the race and during the race by using cold towels, ice, and wearing light colored clothing.

  • Adjust your paces. Use the race pace calculator as a tool to plan ahead on how to adjust paces for race day.






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