The sun is high in the sky, the asphalt shimmers in the heat, and the air is still. It's 2 PM, and you're standing with laced shoes, eyes on the road. You want to go, but how do you tackle a run when the summer heat hits? You'll find out here. Before we dive into how to best handle the heat, let's first look at what actually happens in the body when you run in high temperatures.
Why running in the heat feels extra tough
When you run, your legs pump, arms swing in rhythm, and your body works intensely to propel you forward. It may feel efficient, but actually, only a small part of the energy your body produces goes to the movement itself. The rest turns into heat.
Heat is, in other words, a kind of side effect of moving, and a lot of it is produced. In fact, up to 70-80% of the energy you convert turns into heat. The body must get rid of the excess heat to keep the temperature stable (Duffield & Dawson, 2016). If it doesn't succeed, your body temperature rises, affecting both comfort and performance. The body only functions optimally within a narrow temperature range.
Fortunately, the body has its own systems to get rid of excess heat. It sends blood closer to the skin's surface and starts producing sweat. When the sun beats down from a cloudless sky and the air is still, it becomes much harder for the body to shed the heat.
So what do you do? Should you skip the run when the temperature rises? Fortunately not. It's about helping the body a bit. There are several simple and effective tips that can make your run in the heat more comfortable.
Tip #1 - Train your body for the heat
You get better at running in the heat by practicing. It sounds simple, but it works. Studies have shown that the body begins to adapt after just 5-7 days of light training in warm conditions (Philp et al., 2022; Cole et al., 2023). Your sweat production becomes more efficient, your heart rate doesn't rise as quickly, and you can better maintain a stable body temperature.
Heat training has become a popular method among both elite athletes and ambitious recreational runners in recent years. By exposing the body to heat through training in warm environments or sauna sessions, you can stimulate the body's ability to handle heat more effectively. Physiologically, this includes an increase in plasma volume, a higher sweat rate, and an improved ability to store and manage heat (Sawka et al., 2011; Périard et al., 2015; Garrett et al., 2012). These adaptations not only make it easier to endure the heat but can also help improve your performance.
Training your body for the heat can definitely pay off, especially if you have an important race on the calendar over the summer.
Tip #2 - Dress light and bright
Clothing matters more than you think. Dark clothes absorb the sun's rays and heat up quickly. Light colors, on the other hand, reflect the heat and help you keep the temperature down. Therefore, it's a good idea to choose clothes in white, light gray, or other light shades when running in the sun. A light cap or visor protects the head and face from direct sun and can make a big difference in how warm you feel.
The material also plays an important role. Choose technical running gear that effectively wicks sweat away from the body and allows the skin to breathe. It helps keep you dry and cool. Some modern running clothes are also developed with cooling properties that actively help keep the body cool in warm conditions. This can be an advantage, especially if you run a lot in the sun.
Tip #3 - Drink smart
Fluids and electrolytes play a crucial role when running in warm conditions. When you sweat, you lose not only fluids but also salts. It's not about drinking as much as possible, but about drinking smart.
Runs under 1 hour: It's often enough to be well-hydrated throughout the day, especially in the hours leading up. Electrolytes before departure can be a good idea if you sweat a lot. You can also benefit from carrying a small bottle in your hand or pocket, so you have the option to drink along the way.
Runs over 1 hour: Ensure you're well-hydrated by drinking regularly in the days leading up. Preferably with electrolytes as a supplement. It's not about drinking extra, but about avoiding dehydration. Consider taking electrolytes before starting and supplementing along the way. A
or another option for drinking along the way is an advantage.
It's worth remembering that too much water without electrolytes can cause stomach issues and reduce performance. Therefore, it's often recommended to aim for about 400-800 ml of fluid per hour (Sawka et al., 2010), depending on your sweat rate and the heat. A drink with some carbohydrates and electrolytes can make a noticeable difference in how you feel and perform.
Tip #4 - Run early and start "cool"
The timing of your run is crucial in the summer heat. Early morning and late evening are preferable when the sun is lower, and the temperature is more manageable. Avoid the time between 12 and 3 PM when the sun is strongest and the asphalt almost radiates heat.
You can also help your body before you start running. If you start "cool," your body has more time before reaching temperatures where performance is affected. A cool shower, a stay in a cooled room, or a cold towel on the neck for a few minutes before departure can make a noticeable difference.
Tip #5 - Seek shade and wind
Route choice can make a noticeable difference when running in the heat. Opt for stretches with shade, such as in wooded areas, green paths, or between buildings that shield from the sun. Soft surfaces like gravel and forest trails reflect less heat than asphalt and often feel more comfortable.
Also, consider the wind direction. A light headwind can be beneficial as it helps evaporate sweat and cool the body. Plan your route so you have the headwind on the way back when you're warmest. It may feel tough, but it helps the body more than it hinders the pace.
Tip #6 - Adjust pace and expectations
When the temperature rises, the pace should drop. It's not a defeat but a smart adjustment. In the summer heat, the body, as mentioned, works under extra pressure. This can make even familiar distances feel harder, and that's completely natural. Therefore, it's important to adjust your expectations and pace to match the conditions.
As a rule of thumb, you can start by slowing down 15-20 seconds per kilometer. Listen to your body along the way. If it feels strong, you can increase the pace a bit. If it feels heavy, it's perfectly okay to take it easy. Use your body's signals as a guide, not just the watch and your pace. If you feel like you're overheating, give yourself permission to stop and take a short break in the shade. It can be enough to lower the temperature and give your body a little breather so you can continue the run.
It's rarely on the very hot days that you should chase your new PR. Instead, these are the days where you strengthen your ability to run smart. When you respect the conditions and listen to your body, you can still have plenty of good and rewarding runs while the sun beats down.
Ready, set, summer run!
You're standing there again. The sun beats down, the air shimmers, and shade is scarce. But this time, you know what to do. You've thought about the route, taken a sip of water with electrolytes, slowed the pace a bit, and chosen the light, white t-shirt over the black one. So enjoy the run – and remember the sunscreen.
References:
Cole et al. (2023). Short-term heat acclimation for aging populations. PLOS ONE, 18(3).
Duffield & Dawson (2016). Cooling interventions for athletes. Temperature, 3(2).
Garrett et al. (2012). Short-term heat acclimation in athletes. Eur J Appl Physiol, 112(5).
Périard et al. (2015). Heat acclimation mechanisms and applications. Scand J Med Sci Sports, 25(S1).
Philp et al. (2022). Heat acclimation and rowing performance. PLOS ONE, 17(9).
Sawka et al. (2007). Exercise and fluid replacement. Med Sci Sports Exerc, 39(2).
Sawka et al. (2011). Exercise performance in the heat. Compr Physiol, 1(4).
