Running in the Heat: A Runner’s Guide to Surviving the Summer

A man runs on the trail in an orange glow.

Temperatures are rising and the sun is out. There’s not a cloud in the sky, and the formerly barren branches of the trees are boasting all shades of green. We’ve boxed up our base layers, tossed on a t-shirt and are ready to run with reckless abandon through our local roads, tracks and trails.

Shortly after taking off with a big smile and bouncing stride, you start to slow down a bit. Then a lot. Then (gasp!) maybe even stop running altogether. What’s happened? Conditions are perfect and your legs are fresh. Why does an easy run suddenly feel like so much work?

Don’t worry…you haven’t suddenly lost all your fitness or are somehow “out of shape!” Each year as we climb out from our cold weather cocoons, our bodies must adjust to warmer conditions that affect both our heart rate and the ability to regulate our core temperature. This is a process known as acclimatization (or acclimation), as we literally relearn how to run in the heat.

Why is it harder to run in the heat?

Fundamentally-speaking, we are constantly in a heat exchange with our environments. The increase in metabolic rate during exercise results in an elevated core temperature, which must be regulated in a heat production/heat loss relationship. Our bodies manage this relationship through two mechanisms, by directing heat from the core to the skin via the circulatory system (convective) and by sweating (evaporative).

The goal of this process is to achieve a steady state, or equilibrium, between our heat production and then, our ability to lose (or “dump”) this heat through convective or evaporative methods. However, the metabolic rate during exercise increases immediately while the thermoregulatory systems take longer to respond. This is exactly why you might have started your run feeling like a rock star, only to be holding your hands and knees less than a mile later.

In order to train these thermoregulatory systems to respond more effectively, we must repeatedly expose them to the same stimulus. Practice makes perfect. This is our acclimation period, during which our bodies learn to regulate temperature in order to reach the equilibrium that allows us to continue running in the heat. We eventually improve at this regulation and do it in a way that doesn’t make our heart rate skyrocket and force us into slowing from a run to a jog to a walk.

Two women run on a paved trail wearing tank tops and sunglasses.

Once the body acclimates to the heat, it becomes more efficient at maintaining an ideal core temperature for exercise, which makes running more comfortable and less strenuous. Since the body is able to "dump" the extra heat generated by running through better thermoregulation, exercising in warmer conditions after acclimating allows us to train at the paces we achieved prior to the temperatures rising.

A lot of factors affect the body’s heat response, many of which are entirely outside of our control. Body mass and composition, level of aerobic fitness, and hydration are the variables we can manipulate, but environmental conditions like ambient temperature, dew point and amount of cloud cover also factor into the equation.

It can take the better part of two weeks to be fully acclimated depending, of course, on your protocol. Generally-speaking, about four to six hours of moderate exercise in warm-to-hot conditions is enough to recognize most of the changes associated with heat acclimation.

How to run in the heat comfortably and safely

The good news is, there are several steps you can take to run safely in the heat.

1. Hydration

We all know the importance of staying well-hydrated throughout the day to improve performance, but hydration also plays a pivotal role in thermoregulation. Studies have shown that drinking plenty of water will help your body get rid of excess heat, keep your core temperature at a reasonable level and achieve the steady state heat production/loss ratio. Plus, replacing lost electrolytes and carbohydrates by adding a drink mix to your water can help you recover more quickly.

A man smiles as he sips from his hydration pack in the forest.

2. Ignore your watch and run by feel

Slow your pace by using Rate of Perceived Exertion (RPE) or heart rate (HR), instead of pace or power output. Your usual pace will be significantly harder to maintain until properly acclimated to the heat, so there is no need to force the issue. Instead, run at an effort level that is similar to what you are used to and comfortable with and don’t stress about the fact you might be a little slower than average. If you don’t do this intentionally, your body will do it automatically. A relaxed 30 minute jog at a slower pace is better than a 12-minute sufferfest and blow up at your regular pace.

3. Be patient with the acclimation process

Just as you should take your time during each workout session, practice patience day-to-day and week-to-week. The acclimation process is just that, a process. It will take several weeks of running before you turn a corner, but it will happen! Ironically, you can accelerate this process by slowing your pace during workouts on hot days. By slowing down, you allow your body more sustained time exercising in warm temperatures, which in turn, expedites the acclimation process.

A man and woman run together while the sun rises.

4. Run harder efforts in cooler temperatures

Don’t hesitate to adjust or manipulate your environment in order to perform more strategic, targeted workout sessions as part of a progressive training plan. If you are in the stages of preparing for an upcoming race and absolutely need to get in interval sessions, try to run them earlier in the morning or later in the day when temperatures are a little lower. Maybe you have a race pace workout on the schedule? Find a shaded environment like the trails where the ambient temperature is a bit lower for an up-tempo run. You can even break a long run into two shorter ones. There are always options that will enable you to perform quality sessions during the acclimation period.

5. Stay cool on the run

This may sound obvious, but it’s easier said than done when the temperatures are rising the sun is out in full force. However, you can fight the heat with some simple cooling methods. Maybe you like to wear a hat to block the sun when you run. Try dipping your hat in cold water before putting it on, letting the water run down your back. Some athletes even like sticking ice cubes in their sports bras or shorts to stay cool for as long as possible. As the ice melts, the cold water will drip down your body. Surface area is an important component to staying cool, so any way you can douse a larger area of your body in cold water (or ice!) is incredibly impactful for the simple reason that it affects a larger portion of the exposed surface area.

Remember, it’s important to be aware and mindful of the signals your body is sending you during your run. The difficulty you feel during those first few weeks of running in the heat is your body’s way of telling you it is, quite literally, overheating and you will need to make the necessary course corrections to avoid negative outcomes such as heatstroke. Understanding the physiological processes that are happening in response to the heat will help better inform how you can best respond in each situation. By responding with intent, rather than just reacting to the environment, you can get the most out of each session and get back to enjoying the warm weather runs as soon as possible.

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