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Updated: Aug 8, 2023

Did you know, running in the heat of the day can actually boost your fitness more than running in cool conditions? If you need a little extra motivation to get out the door on the warm days that are upon us, read on to learn about heat training, and why athletes train in the heat on purpose to boost their fitness.

Athletes implement a variety of strategies to optimize their training and get a competitive edge. You have probably heard of athletes using altitude training. However, there are some ways you can optimize your training without having to travel up a mountain. Another “stressor” athletes manipulate to maximize training effect is heat training. Many summer races require athletes to compete in blistering conditions, from famous ultra races like Western States, to track meets during Eugene heat waves. What do elite athletes do to prepare for these conditions? Also, what can you do to best prepare yourself for those scorching summer races?

Training hard and racing in warm weather certainly puts extra strain on your body. When running in hot conditions, your body’s core temperature increases more quickly, limiting your body’s ability to effectively cool itself. In turn, the strain on your cardiovascular system increases exponentially. When your body starts to heat up more than usual on a run, this sends warning signals to your brain. Your brain reduces your work rate, forcing you to slow down.

However, significantly reduced running performance in hot conditions is not guaranteed. In fact, our brain dampens the force output of our cardiovascular and muscular systems far before we reach a level that presents danger to the body. Just like training can be used to improve our tolerance of running at uncomfortable paces, heat training or “heat acclimatization” can be implemented similarly. Let’s take a look at what the research tells us regarding how best to approach heat acclimatization training.


The best approach to maximize heat adaptations is repeatedly exercising in warm conditions. Heat exposure over the course of 1-2 weeks has shown the best results. Studies assessing time trial performance in cyclists undergoing heat acclimation found notable improvements when cyclists were re-tested in both cooler and hot conditions, with the more notable improvement being in hot conditions (by 8% compared to 6%). This is consistent with the concept of specificity. When it comes to training, replicating the environment you want to perform well in is going to prepare you most closely for said performance.

Other studies have looked at different methods of heat training, comparing wearing excessive layers in moderate conditions, compared to training in hot conditions. This research found that training in sweat-inducing layers had a similar benefit as training in a hot humid climate.The good news here is that you can prepare yourself for racing in a hotter climate, even if your usual training environment is temperate.

Piling on extra layers and going for a jog in the heat of the day are not the only strategies for improving heat tolerance. Going to the sauna after exercise has been shown to boost endurance performance. A small cross-over study on male distance runners evaluated the effects of post exercise sauna on endurance performance. They concluded that sauna time can create a measurable increase in endurance performance, likely related to increased blood volume adaptations.

HOW the Body Adapts:

Research has found that heat acclimatization enables the body to better regulate temperature (thermoregulate) in heat, by increasing the efficiency of various thermoregulatory mechanisms. The mechanisms signaling your brain to slow down when the body temperature warms can become more precise, meaning they are not sending the warning signals to the brain as soon as they would for the un-heat trained athlete.

One large and robust meta-analysis (although over 85% of the studies only studied male athletes), also concluded that cardiovascular adaptations are likely the leading driver of improved heat tolerance experienced with heat acclimatization. Essentially, the heart and lungs become more efficient, and will be less affected by reduced blood volume as the body works overtime to maintain a stable core body temperature. Some research suggests an increase in blood plasma results from heat training. An increase in blood volume equates to a more efficient cardiovascular system, and thus more aerobic power.

How Long Does it Take?

As alluded to above, it takes about two weeks of repeated exposure to reap the full benefit of heat acclimatization training. Some studies have found adaptations to heat training to occur as early as one week after repeated moderate intensity exercise exposure. However, the loss of adaptation occurs more swiftly. Once you are acclimated, it only takes a few days for the benefits to start to decay. One study estimated the rate of decay of the benefits to be 2.5% per day once the heat exposure is removed.


When exercising in the heat, there are some key safety considerations to keep in mind. Just like with adding in any other new stressor to your running routine like adding intensity (workouts) or more mileage, we must always do so gradually. This way, the body has time to adapt to the new stress and respond in an advantageous way. If we apply too much stress too quickly, the body does not have time to adapt, and becomes overworked. This is when our risk of injury or illness is increased due to lack of recovery.

Thus, to approach heat training safely, we should:

  • Optimize fluid intake prior to and during heat exposure exercise

  • Avoid factors known to decrease tolerance to heat:

    • This includes sleep loss, illness, etc

  • Allow easier intensity, and rest as needed, using perceived effort to guide your run or workout more than a strict time/pace.

  • Make sure to fuel. Research indicates that your body’s carbohydrate requirements increase in the heat due to altered energy demands

When utilized correctly, multiple sources have indicated that heat training is a cost effective method of enhancing fitness. So, next time it’s hot and you are trying to talk yourself into getting out the door to exercise, know that when done correctly, you are encouraging your body to acclimate. This way, you will be better prepared for those warm summer racing conditions.

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