Heat Training And Acclimation – How To Run In The Heat

In this article, I dig into heat training and acclimation and specifically how heat impacts our bodies while running. I then share several heat training tips for runners who need to deal with the high temperatures and humidity that often accompany summer training.

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Are There Any Benefits of Running In The Heat?

Running in warm temperatures may not always be fun, but it can be beneficial. As our body acclimatizes, the impact of the heat on our body lessens.

A lot of us get spoiled from being indoor dwellers and working in places that have air conditioning. We’re not exposed to the heat as much. When I was a kid we had one air conditioner for the whole house, and we only used it when absolutely needed. Most of the time we were playing outside of sleeping with the windows open.

Why Do High Temperatures Slow Down Runners?

We found a study that was published in Medicine & Science in Sports & Exercise by an exercise physiologist, which shows how warm weather conditions impact marathon-running performance.

I’m a little partial to this study just because they only studied male elite and sub-elite just like pro runners, not a lot of women, and normal people like most of us. That’s the problem with many studies because they’re all typically college elite-level athletes.

The nice thing about studying elites though is that it is consistent, you know that they’re putting 100-150 miles per week and that running is what they do. There are not as many variables compared to studying someone like us.

Most distance runners prefer a good 50-degree day. But if you’re running that marathon from 3 to 6 hours, later that 50 degrees can shoot up to 80 or more – that’s really the problem. Here is what this 10-year study of elite male athletes running between 44 – 77 degree temperatures shows:

• 50 degree is actually at some of the slowest times recorded overall.
• Below 40 degree is the prime temperature for top finishers on average.
• Temperatures starting at 30 degrees are the best.
• Temperatures from 60 to 69 degrees are just considered less than ideal. This will slow down a 40-minute 10K runner by 1.7% which is on average about 6s/m off.
• Temperatures from 70 to 79 degrees are the case when an elite male marathoner can expect to lose as much as 3 to 20 minutes off of his overall finishing time.
• For the rest of this 80 to 90 degrees with 70% or more humidity is the point when your body is going to force you to slow down. The amount of heat you produce will not be outmatched by the sweat your produce and the more you sweat the more you deplete yourself, your electrolytes, and sodium. Such a level of heat and humidity will require you to keep hydrating and fueling to continue going.

Once you get over 90 degrees it’s really just dangerous if you’re not acclimated to the heat.

If you have symptoms like nausea or vomiting, don’t hesitate to call 911 immediately.

How Does the Heat Affect Your Body?

Exercising and working the muscles just generate heat and this is great when it’s cold outside but when it’s hot it needs to go somewhere so that’s when your body starts to create sweat to cool you down. The heat from your muscles also promotes a higher blood flow closer to the skin so that the heat can get out as well. The effect of this is your body gets more concerned about you being hot and need to cool off than whatever your muscles are doing.

So you may notice that you’re out of the pool laying around on a hot day not doing much just laying, but still get completely exhausted by the end of the day, and you’re still hungry even though you haven’t done anything.

But your muscles come secondary to your body and your body temperature comes number 1 to your brain, so you feel weaker as the blood flow is being forced to the skin to expel heat out as opposed to helping your muscles work as hard as if it were in a school day.

Our body is constantly trying to thermoregulate itself and that is why when our muscles are moving, it’s generating heat when we have heat coming from the sun and from the air temperature and reflecting off the surface of the ground running on.

Note:  When our body starts to heat up it becomes more important for it to self-regulate its own temperature and to basically preserve itself. That’s why we start sweating, the run seems harder because the fluids in the blood plasma and all the stuff, including fuel, and our nutrients are not going to muscles, everything’s going to your skin to try to keep it cool. And that’s why you can’t go out and run at the same pace and intensity on an 80-90°F day, but you can on a 30°F, 40°F, or 50 °F days.

So if you get into that race when the temperatures are unseasonably warm or you didn’t acclimate properly, then you may have to set your expectations a little bit less than what you anticipated.

If you start exposing yourself to the heat, running during the summer days, you may later on notice how much better blood flow and breathing got, everything just seems to work better together. In other words, you got acclimated.

How Quickly We Can Adapt to the Heat?

So the common opinion on adaptation to the heat is about 10 runs – minimum 10 runs in the heat – which works out to about 2-3 weeks for most people.

But we don’t always have that amount of time to adapt, especially for going to an out-of-town race. So anything you do is better than nothing. It’s about getting out into the heat and actually running. We don’t talk about the dangerous levels here, we’re talking about getting out into what would still be considered safe enough.

If you’re used to running indoors all the time and then all of a sudden you expect to run in 90-degree humid weather, you might get some problems. But if you know that your race day might have 80-degree temperatures or finish in the 80-degree temperatures, it will do you well to go out and get some heat acclimation by just being out.

Note:  Within one week of consistent training what happens is our blood plasma starts to expand and creates the extra fluid in our blood for sweating and this helps prevent early dehydration because our body now is expecting to sweat more. And our sweat gland activation actually nearly doubles, which is really important. Without this gland activation, your body is not able to sweat and cool down itself. It may all end up with heat exhaustion or heat stroke, which is quite dangerous.

And as I was saying earlier, your body temperature comes number one to your brain to cool off and your muscles come secondary. So building that extra plasma also creates the blood flow to the skin with the goal of not restricting it to the muscles, which is why you need that extra blood to stay cool and to keep your pace.

Another thing that occurs is when you start to acclimate to the heat is that you begin to sweat earlier in the workout so our bodies can adapt to warmer temperatures and then we don’t take as long to start sweating.

So in cooler temperatures, you could be running for 2 or 3 miles before you really start working up a sweat.

If you’re out in warmer temperatures, you start running, and you start sweating almost immediately because it’s hot outside, because your body is trained, and because you have these extra sweat glands.

And not every gland is activated at first, because our body doesn’t need it. Your body doesn’t need the sweat as much when temperatures are cool but as it warms up, those things start to kick in.

How to Adapt to the Heat?

If you’re getting ready to head into summer, and you’re finally getting some runs outside because there are races coming up, the best advice I can give is to run outside.

If you have been training all summer, you probably do feel pretty acclimated especially if you live in an area with high humidity.

If you’re traveling to a warm area and you are not able to run outside in the hot weather before you leave and you don’t get a whole lot of warm weather, there are other options to get acclimated:

• Sauna
• Hot tubs
• Heated rooms
• Wearing additional layers of clothing (it can add approximately 15 degrees to your body temperature)

I know a runner who participates in tough races through the desert. In order to get acclimated, he puts the treadmill inside a small room and turns on the heating up to over 100 degrees to experience what it’s like to run out in the desert.

Many other runners do similar things like using hot tubs and increasing the amount of time in a hot tub each time. You can also turn off the air conditioning on Sundays, go out and work in the yard in the afternoon just to be exposed to the heat at least for a few hours.

Athletes sometimes use such heat elevation strategy as training with sauna suits to acclimate to hot weather conditions. The study shows that 2 weeks of training with a sauna suit increased sweat rate, lowered core temperature, and helped improve VO2max and time trial performances.

Tips for Acclimation and Running in the Heat

Increase the Exposure to the Heat Gradually

• If you’re going to run in the heat, just start slow, don’t have a high pace expectation because it’s just gonna take a little bit to get there.
• If you’re not used to high temperatures at all, don’t make your first run outside long.
• If you’re not used to running in the heat, don’t start training at noon. It’s better to start a little bit earlier in the morning or hold off until later in the day when it’s getting cooler.

Support Proper Fueling and Hydration

If you’re gonna be out in the heat, obviously stay hydrated. Сarry the bottle with fluids, or keep it in the car so you can easily access it. The hotter it gets, the more you’re sweating, the more you’re losing fluids, and the more you need to replace fluids.

If you’re gonna be out longer than an hour electrolytes become especially important because you’re gonna sweat out the sodium, potassium, and other types of electrolytes that have a pretty important role in your training. So you want to make sure that you’re continuing to drink and just really test what balance you need that’s gonna be right for you.

You should also consider the warning signs of heat illness as well as heat exhaustion and heatstroke. It can come on very quickly, and it’s dangerous. This is a reason why you have to really think about slowing things down.

On those hot days, it is very important to take extra long breaks at the water stops and just allow our heart rate to kind of come back down to normal. Your heart rate will tend to spike, and your body temperature will start getting really high, and this is when you should not be stressed out about pace, it’s just important to be out there.

Every little effort may cause our heart rate to start spiking so it’s very hard to maintain that faster pace. That’s why it’s okay to take more frequent stops on those hot days to regulate your heart rate and get hydrated.

You can mark a place on your course where you could just stop, use a cooling towel, or swish the electrolyte drink around your mouth. If you’re not feeling well, part of the issue is probably the dehydration aspect but if you at least rinse out your mouth a little bit with it and spit it out, that’ll help.

Read Also: The Basics Of Endurance Fueling – How To Use Gels, Wafers And Sport Beans

What to Wear for Running in the Heat

First of all,  wear clothing that is light and colored, so it’s reflecting the heat not absorbing heat. Also, get a hat to keep the sun off your face.

Note: We lose a lot of heat through the head. In fact, 20-30% of our body heat is lost through our head in the wintertime, which is why you want to wear a hat. On the other side, if you wear a hat in the summertime, you simply trap the heat in. That’s why if you have the ability to wear a visor that has an open-top design, that’s gonna let a lot of that heat out.

Now obviously if you’re bald you might not want to have your head exposed to the heat and apply some sunscreen to it. And if you have dark hair that attracts the sun, you might also prefer a hat made with proprietary fabric that cools instantly.

I personally recommend a light-weight visor that contains a quick-drying sweatband, however, this option is not for everyone. Finally, if you don’t want to wear any hat, but want to keep your head cool, a cooling headband is the best solution.

Last update on 2025-07-02 / Images from Amazon Product Advertising API

Last update on 2025-07-02 / Images from Amazon Product Advertising API

Don’t Rely on Cooling Sleeves and Pouring Water

A lot of people are recommending cooling sleeves and cooling fabrics that you can wrap around your arms and then pour water on them at the water stops to stay cool.

However, pouring water on cooling sleeves is not as effective as you might have thought. As one study shows, it gives a temporary cooling effect by keeping old sweat on your bare skin. The wrapping of your skin with fabric is actually restricting the ability to sweat, holding in body temperature.

So it’s heating the body up and it only feels good for a few minutes when you’re pouring water on, and then it starts working against you.

Key Takeaway: I don’t say that cooling sleeves don’t work at all, they provide some protection from the sun. Also, if you ride a bike, you move fast, and you get a better airflow, which wicks away the heat better. So when you use them on the hot race on the bike, cooling sleeves can be quite useful. BUT when it comes to running, it works a bit different, the air exchange on the arm is not as good, so sleeves start to heat up and trap the heat. And as I’ve mentioned before, when you pour water on the cooling sleeves, it will give only a short cooling effect. Therefore, when running, it’s better not to cover up the skin, because there’s nothing more effective than the skin and your body’s ability to sweat.

 

Get off the Roads and Try More Trail Running

I also want to point out that we often think that it’s all about air temperature, humidity, the sun beating down on us, we tend to forget about running on dark running surfaces like for example newly covered asphalt: reflected heating is coming down and reflecting back upon us.

On a hot summer day, asphalt can raise the temperature within a few feet of the ground as much as 10 to 20 degrees in some cases. So there could be an 80-degree air temperature but if you’re running it on a dark running trail, you’re adding another 10 to 20 degrees potentially to the air temperature around. So try to look for those places where you can get off the trail, maybe that’s running alongside the trail in the grass if it’s worn down and packed down or running on older asphalt like the road.

Read Also: 10 Tips Every Runner Should Know About Running in the Heat

Bottom Line

• When it’s hot outside, go to the parks and trails where it’s nice and shady. If you can find places that have shade along the trail, that’s ideal. Avoid the hottest part of the days just for safety reasons.
• We don’t necessarily have to be acclimating while we’re running we can just get out into the temperature.
• You have to be willing to change your goal or expectation on a particular day. If on the race day the temperature goes up to 90 degrees, and you’re getting off your time goal because of the heat impact, don’t get upset, believe in your training, and always remember that there are factors like weather that we cannot control.