It’s finally starting to feel like summer in the northern hemisphere, which means more opportunities to venture outside for a run instead of hitting the gym.
Running in the heat poses its own unique set of challenges. Hot weather can make you feel sluggish because your body has to work harder to keep you cool while pumping blood to your muscles. More seriously, it’s easier to become dehydrated in the heat, which, in tandem with overheating, can lead to complications like heat cramps or in extreme cases, heat stroke.
With the right kind of preparation, however, there are safe—dare we say, even enjoyable—ways to run in the sun.
The right gear can make all the difference, says Karen Smith, a dietician with Barnard Medical Center and five-time marathoner. As temperatures increase, you’ll want to wear less clothing to stay cooler, but the type of fabric you do wear matters. Stick with sweat-wicking clothing, like polyester materials. “Cotton is just going to soak up the sweat and be heavy,” said Smith. She also recommends moisture-wicking socks to avoid blisters.
Less clothing means more exposed skin. If you’re going to do any activity while directly exposed to the sun, it’s important to apply a sport sunscreen about 30 minutes before you leave. Bring some with you to reapply on longer runs. And to avoid the red, raw, and sometimes bloody skin caused by chafing, you may want to invest in some kind of anti-chafing body glide, which you can find in most athletic stores.
You’ll also be sweating more. It’s our body’s way of trying to keep us cool, but in the process we lose much-needed water and electrolytes, like salts, which can cause dehydration, a confounding factor in heat cramps. “Every runner should have at least a 24-ounce water bottle that they refill throughout the day,” Smith says. If you run first thing in the morning, try to drink at least 16 ounces before you leave, and carry water with you for runs longer than 40 minutes.
After your run, make sure to replace any water you may have lost. Sports drinks with some sugars and salt can help replenish your body’s electrolytes. You can regulate your hydration by checking the color of your urine, Smith suggests. If it’s generally pale, you’re well-hydrated.
If running feels harder in the heat, that’s because it is. A high dew point, which indicates high levels of water vapor in the air, can make us feel sluggish. You shouldn’t venture out for a run at a dew point of more than 75°F (24°C). We also feel lethargic because our blood is forced to take on double-duty in the heat. Our body needs to draw in blood to get oxygen but also has to pull it to the outer edges of our skin to help us cool off. The result is that we’re going to move more slowly, or be less able to sustain a faster pace for longer periods of time.
At any temperature, if you feel signs of heat-related illness, like extreme cramps, headaches, nausea, or dizziness, you should stop running, retreat somewhere cool, and hydrate.
If you still want to reach a certain mileage, go in the cooler early morning or late evening and try to plan your routes to encounter some shade. Listen to your body, Smith advises. “You can expect to be slower, so having that mentality…and not pushing it is important.”
You may not hit a personal record in the high heat of summer, but small studies have shown (paywall) that training in hot conditions can actually increase your performance in cooler temperatures later on. Fall race, anyone?