Three Ways to Get Used to Working Out in the Heat
No one likes feeling sluggish and sweaty, so when the sun goes down, many of us prefer to work out in an air-conditioned gym. But the human body can adapt to working out in the heat, so it might be worth heading outside. After a few weeks, this temperature will become your new normal, and research shows that you may notice a slight boost in performance when the weather cools again.
Running in the heat can be dangerous, so I’m sure you know the basic rules for running in the heat. Among the most important: drink as much as you need (or a little more), and stop and seek help if you experience symptoms of heat stroke, such as nausea, dizziness, or weakness. And while it’s helpful to work on your ability to run in the heat, don’t be foolish—stay home if the temperature is higher than you can handle , and monitor the air quality (which worsens on hot days).
Why is exercising in the heat so unpleasant?
Running is hard, and so is the heat, so running in the heat is hard. But that’s not all, and exercising in the heat is much worse than you might expect, given the combination of these two factors.
Exercise increases body temperature, and when combined with heat, it can easily reach dangerously high levels. This means the body has to work harder than usual to cool itself down. The methods used to cool down also affect the effectiveness of exercise. For example, the heart works hard to supply blood and oxygen to the muscles and to pump blood to the skin’s surface for cooling. These tasks require a great deal of effort—it’s no wonder we feel exhausted in the heat.
As a protective measure, the brain processes stress differently in hot weather, so you feel sluggish even before you overheat. In a study published in the European Journal of Physiology , cyclists training in a lab at 95 degrees Celsius (205 degrees Fahrenheit) performed worse than those in a similar time trial at 59 degrees Celsius (130 degrees Fahrenheit). This makes sense, but here’s the strange part: they didn’t overheat and then slow down. They were slower from the start . It seems our brains preemptively slow down our bodies on hot days to conserve energy.
As we exercise, our bodies heat up. In another study published in the Journal of Applied Physiology , participants who were asked to pedal to exhaustion quit when their body temperature reached 40 degrees Celsius (104 degrees Fahrenheit), regardless of their starting temperature. This is the temperature at which severe heat exhaustion can occur, so it’s logical that the body slows down at this point. In this study, athletes who cooled themselves with cooling vests lasted the longest. (You can mimic this effect in your training by drinking ice-cold drinks and pouring water on your head .) The longer you can maintain a cool body temperature, the longer you’ll be able to sustain intense exercise.
It’s the heat and humidity.
But cooling the body is not a panacea. Pouring a glass of ice water over your head or applying it to your stomach provides only short-term relief, and cooling vests are impractical outside of physiological laboratories. So let’s look at what happens in real-world conditions.
The most effective way to cool yourself is by sweating. When moisture evaporates from the skin, it carries away some of the body’s heat. However, in humid weather, sweat doesn’t evaporate as easily because the air is already saturated with water vapor. So when we talk about “warmth,” we’re actually talking about more than just “felt warmth,” which is a combination of warmth and humidity. This heat index chart illustrates this relationship:
In hot weather (and high humidity), you’ll run slower. While you can find charts like this one that predict how much slower you’ll run, the truth is that the impact of heat on your running depends on how accustomed you are to heat and your body size.
That’s right—it’s not your level of fitness that matters, but your actual body size. Larger people tend to have larger frames, more muscle, more fat, or both. Muscle generates heat, while fat acts as an insulator. On the other hand, smaller people generate less heat but have more skin to dissipate that heat through—the good old principle of surface area to volume ratio . This is why shorter runners perform better in races on hot days.
Some people believe that being in good physical shape helps them tolerate heat better, but this is only partially true: the fitter you are, the more heat your body produces , simply because you’re working out so hard. Besides changing your body shape (which is possible, but hardly a short-term solution), what can you do to better tolerate exercise in hot weather? The answer is simple: spend more time exercising in the heat.
Why You Should Start a Heat Adaptation Protocol
Running in the heat improves your running skills in the heat—and your overall performance. Let’s say you’re training outdoors this summer, and your equally athletic twin is doing identical workouts on a treadmill in an air-conditioned gym. Who do you think will finish first in a 5K on a hot August weekend? That’s right, you.
But even if the weather is unusually cool on that August day, your heat training will still help you outperform your twin. Part of the magic of heat training is that it increases the amount of blood in your veins (to better direct it to the skin for cooling, while still providing sufficient energy for your muscles). This effect has been compared to a mild, completely legal version of blood doping. Scientists are still debating exactly how this effect works and whether it always occurs when people try to adapt to heat, but overall, the evidence is compelling enough that I believe we should all try to achieve some of these adaptations if it’s safe to do so.
Here’s the bad news: adapting to heat takes effort. It’s not enough to simply sit in an air-conditioned room all summer, only venturing outside for occasional exercise. A study published in the European Journal of Applied Physiology found that people who didn’t make a significant effort to exercise in the heat didn’t demonstrate better heat tolerance in the fall than in the spring. If you want to reap the benefits of exercising in the heat, you’ll have to put in the work.
Below I’ll discuss some heat adaptation strategies, but the general idea is to spend at least two weeks in the heat. Your body will learn to cool itself better, and hot runs will feel a little easier. However, heat adaptation isn’t magic. You’ll still feel hot and may run slower than you would in cooler temperatures. You’ll just be able to get through most of your workout before your body temperature rises to dangerous levels. If you’d like to learn more about training in the heat, I wrote about my experience last year with a heat training tracker , which allowed me to get detailed information about how my workouts are going in the heat.
How to Adapt to Exercising in the Heat
Option 1: Train as usual, but do not avoid the heat, for two weeks.
In scientific studies, heat acclimation protocols for athletes typically include 7-10 consecutive days of 60-90 minute heat training each day. A simpler method, which can be used by entire teams or individual athletes, is to simply conduct normal heat training for approximately two weeks.
Start small. Remember that your body is still trying to convince you that you’re very tired and need to slow down. This is where safety guidelines for workers can help. On the first day of working in the heat, the Occupational Safety and Health Administration (OSHA) recommends giving workers just 20% of their normal workload. Over the course of a week, they should gradually increase their workload to 100%.
Option 2: Spend two hours in the heat every day, whether you exercise or not.
This US Army training protocol offers a good plan for heat adaptation: it recommends spending at least two hours a day in the heat, including cardio (such as running, cycling, or any other exercise that raises your heart rate). If you can’t make it two hours without experiencing symptoms such as nausea or dizziness, do your best and consider the two-hour limit a goal to strive for.
After about two weeks of spending two hours a day in the heat, you’ll likely become more acclimated to it, although results may take just a few days to become noticeable.
Option 3: Visit the sauna after each workout.
One way to combine the protocols described above, regardless of the weather, is to visit a sauna or take a hot bath after your workout. If your gym has a sauna, this is a great way to use it. Spending time in the sauna after your workout will help your body adapt to the heat, and this can be done even if your workout was done in cooler weather.
Sauna time can range from 15 to 30 minutes, starting with shorter periods and gradually increasing them. Note that these guidelines only apply if you use the sauna after a workout , when your body temperature is already elevated due to exercise. If you skip a workout, you’ll need to add about 20 minutes to your sauna time to achieve the same effect.
How to maintain adaptation to heat even when it gets colder.
To stay adapted to the heat, you need to be constantly exposed to it. Taking a few days off is fine, but if you slack off for a week, you’ll start to lose your heat-related “superpowers.” This quickly escalates: the army estimates that after three weeks, you’ll lose about 75% of your adaptations.
To continue training in the heat in cooler weather, you can try wearing long sleeves and leggings, as elite runner Kara Goucher did while training for the World Championships in sweltering Osaka. (She won a bronze medal, becoming the first American woman to do so.) She also spent several weeks in Osaka before the competition; a trip to experience the heat might be worth considering if you’re a dedicated athlete with time to spare.
You can also try the opposite approach to all the standard advice for staying cool and choose to run during the hottest part of the day on paved roads without shade. Or, return to visiting the sauna after your workouts in cooler weather. Whatever you do, be careful and enjoy your new superpowers.