Heat Training for Runners: How To Prepare For Hot Races

Tips and tricks to heat train when the weather is too cold to do so outside.

If you’ve been a runner for a year or two, you’ve likely had the following scenario.

It’s fall, winter, or spring. You’ve been getting used to the cooler temperature and are preparing for an upcoming race.

A week out, you check the weather and notice it’s going to be warm on race day. Not just warm, it’s going to be hot.

What do you do? How do you prepare? How do you heat train to prepare for hot races?

In this guide, we will discuss what happens to our body in the heat and what heat adaptations we can make for efficient and safe heat training for runners.

A person running in the heat.

One note before we get started. Exercising in heat can be incredibly dangerous and should not be done lightly or on a whim. It is very easy to overdue heat training and wind up with heat exhaustion or heat stroke.

Please take special care if you decide to try any of the training tactics in this article. Seek advice from a medical professional if you have past medical conditions that could be affected by heat exposure and exercising in the heat.

I was getting ready for Canyons 100k in April of 2023. My training went well over several months, and I was prepared for the distance and the hilly terrain. 

Two weeks out, I checked the weather. 90 degrees. Hot conditions. That was the forecast for race day.

I live in Colorado, and the temperature had been hovering between 40-60 degrees Fahrenheit for most of the preceding months.

I knew I was completely unprepared to race long distances in high temperatures. I needed to prepare my body as much as possible for the conditions I would face.

So, I did some research on heat training for runners and heat acclimatization.

Beads of sweat on a person's face.

What Happens To Our Bodies As It Gets Warmer?

“I don’t race as well when it’s hot.” You’ll hear me exclaiming this to anyone in earshot in the warmer months of the year.

The truth of the matter is none of us do. Once the temperature starts climbing, we see a decrease in running performance.

Why is that? What happens to our bodies in these hot and humid conditions?

You might figure it’s because you are dehydrating quicker. That is certainly the case in hot environments. Dehydration can lead to a lower cardiac output and affect our blood pressure. But that is just the start.

Part of running efficiency is the ability of your body to get blood to your muscles. Blood carries oxygen, and our muscles need this to work during aerobic efforts.

In hot weather, our bodies are working to cool themselves. They do this by producing sweat. This draws our blood to the skin to help cool the body.

So instead of all that blood flow going to our muscles to keep them fed with oxygen, some of that blood will help cool our bodies. This means our body has to pump more blood to get the same amount of oxygen to our muscles.

This results in us having to expend more energy to maintain the same pace. It also leads to an increase in lactate production and an elevated heart rate.

What temperature does this start taking effect? Around 60 degrees Fahrenheit (15 degrees Celsius).

Numerous research has shown that the ideal temperature for a marathon is between 44-59 degrees F (7-15 degrees C). Above this range (or lower, but for different reasons), our performance begins to decrease.

The temperature range is a bit wider for shorter races, but there is no mistake: As the mercury begins increasing, our athletic performance decreases.

A person running in the sun.

What Adaptations Take Place As We Adjust To The Heat?

When we run in the heat, certain adaptations take place that can improve our efficiency and endurance performance and make us better runners.

These adaptations include:

  • Improved Vo2 max and lactate threshold
  • Improved cardiac output
  • Reduction in core temperature 
  • Reduced resting heart rate
  • Increased sweat rate

Let’s dive into each of these a little further.

Improved VO2 Max and Lactate Threshold

VO2 max measures the amount of oxygen you consume during intense exercise, and lactate threshold is the rate at which lactate builds in the bloodstream faster than your body can remove it. Both of these determine how hard you can run during races. 

As your body acclimates to heat, these metrics can improve, which means you can run harder efforts and see increases in race performance.

This study done in 2010 showed that athletes training in hot weather for ten days saw 5-6 percent increases in their Vo2 max, power output at lactate threshold, and time trial efforts.1Lorenzo, S., Halliwill, J. R., Sawka, M. N., & Minson, C. T. (2010). Heat acclimation improves exercise performance. Journal of Applied Physiology109(4), 1140–1147. https://doi.org/10.1152/japplphysiol.00495.2010

A person running in a sweatshirt.

Improved Cardiac Output

Cardiac output is the body’s ability to get blood through the blood vessels to muscles. As your body adjusts to heat, you can sustain a higher blood pressure, allowing you to pump more blood through your body.

Reduction in Core Temperature

As you heat train to prepare for a hot race, your body’s core temperature will lower.

This is helpful because as your core temperature rises, your cardiac output decreases. Starting with a lower core temperature and having it heat slower means that you can maintain a higher cardiac output for longer.

Reduced Resting Heart Rate

Having a lower resting heart rate is an obvious benefit. The reduced heart rate means that you can maintain harder efforts with less strain on your body. Having a reduced heart rate also aids in improved cardiovascular stability.

Increased Sweat Rate

What separates humans from most animals is our ability to cool ourselves by sweating.

As our body acclimates to hot weather, we begin sweating sooner and more profusely to cool ourselves down. Our bodies can even adapt to conserve sodium and not sweat it out as quickly, which helps our bodies retain water longer.

If some of the performance increases sound familiar, it’s likely because these adaptions can have remarkably similar effects to altitude training.

Since most runners are unlikely to be able to move to altitude to train or afford an expensive altitude tent, heat training can be a convenient way to get similar benefits for runners to improve their efficiency.

A person in a hot tub.

The Different Types Of Heat Training For Runners

There are two types of heat training runners can implement into their training: passive heat training and active heat training.

Passive Heat Training

Passive heat training is the easier of the two. It involves subjecting yourself to warm temperatures while not exercising.

Some common methods involve saunas, hot tubs, or hot baths. This can be difficult because a lot of us may not have access to the first two. However, the hot bath is a great option.

In the final two weeks leading up to Canyons 100k, I would take a post-run bath every other day. My bathroom is small, and I would shut the door and leave the vent off to create a sauna effect.

I would make the water as hot as I could stand and sit in the tub for 20-40 minutes. Then I would rehydrate well afterward. Subjecting my body to water over 100 degrees F forced my body to figure out how to cool itself.

I would also dump Epsom salt in the bath, which helped soothe sore muscles. This is something I do after long runs, and I feel it helps with recovery.

Having access to a sauna can help you even more. A lot of saunas can heat up to well over 150 degrees. I’ve read articles about runners pulling treadmills into saunas and running on them to prepare for notoriously hot races like Badwater.

While I would not recommend this at all, sitting in a sauna to prep your body for a hot race can have amazing benefits on race day.

Passive heat training can pass along some benefits, but to prepare for hot races, you will need to engage in active heat training as well.

A person in a hot bath as a way of heat training for runners.

Active Heat Training

Active heat training involves exercising in the heat or simulating it to the best of your ability in your training plan.

The most obvious way to achieve this is to get out and do some hot weather running when possible. It’s best to start with easy runs and build into longer efforts. If you are doing intervals or other hard efforts, keep them shorter than usual.

Also, ensure you hydrate appropriately before, during, and after these efforts.

What if you live in a cooler climate and are traveling to a warmer climate? This is the situation I was in leading up to Canyons 100k.

The easiest method here is to wear additional layers on runs. You can also couple this with indoor runs on a treadmill.

There were several days where it was 40 degrees outside but 60-65 in my house. On those days, I would run an easy 30 minutes on the treadmill in a long-sleeved shirt and hoodie to simulate a hotter environment.

Running on a treadmill.

I’ve also seen runners with treadmills in a garage or shed use heat lamps to increase the heat further. This could help increase the temperature, but it seems a little more dangerous than I wanted to do.

To reap the benefits from heat training, you generally need 10-15 days, although well-conditioned athletes can see results in about half the time.

Finally, it is worth noting that you don’t have to use these principles strictly for hot races. As mentioned earlier, many benefits from heat training mirror those from high-altitude training.

You can add this to your training to help improve performance for any race, hot or otherwise.

I recently implemented these while preparing for the 2024 Houston Marathon. The weather can be finicky in Texas in January, so I figured I would ensure I was prepared just in case. The weather turned out to be a perfect 45 degrees, and I went on to PR and ran my first-ever Boston Qualifying time.

Did the heat training help? Maybe. It sure didn’t hurt.

A person drinking from a water bottle.

What To Do On Race Day

You’ve done all the training and preparation. Now, make sure you don’t blow it on race day.

For Canyons 100k, I hydrated often and kept extra fluid and electrolyte tabs in my pack just in case. I dunked my hat and neck gaiter in streams and poured water and ice over me at aid stations every chance I got to help keep my core body temperature down.

I also wore a loose white shirt to help keep me cool and not absorb as much sunlight. (And don’t forget your sunscreen!)

Even with your training, you may need to adjust your effort to keep yourself from overdoing it. Be smart with pacing, ensure you are taking in fluids, and keep yourself as cool as possible.

Proper heat training may not lead to a PR on a hot day, but it could save you from a DNF or just make your race more enjoyable.

To ensure you keep well-hydrated in your summer running workouts, check out this next guide:

References

Photo of author
Adam Rabo has been running since junior high. He has coached high school and college distance runners. Adam recently completed the UTMB Canyons 100k, making the cutoff for the Western States 100 and UTMB. You can generally find him on the rodes or trails in Colorado Springs, training for upcoming marathons and ultramarathons.

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