Sports physiology lecturer explains whether running in the heat is advisable

Carmen Reinpõld, a sports physiology lecturer at Tallinn University, told the Novaator portal that running outdoors in hot weather is not harmful at all if the body has adapted to it. However, the first truly hot day in Estonia often arrives unexpectedly. If a person has not trained in such conditions before, the body may overheat because the muscles themselves generate a large amount of heat. This can become dangerous.

To adapt to heat, athletes conduct special training sessions, such as dressing warmer in cool weather or training indoors without cooling. This triggers changes in the body that help it adapt and cool down better—for example, a person starts sweating faster, which cools the body. Since heat tolerance varies individually, there is no specific temperature above or below which one should avoid running. Temperatures above 30°C are initially difficult for almost everyone, but anyone can gradually acclimate, for instance by dressing a bit warmer during runs.

Adaptation training must be done regularly, otherwise the body quickly returns to its comfort zone, but such sessions should not be performed every time. It is never too late to start these trainings. If done three to four times a week, signs of adaptation become noticeable within at least two weeks. How quickly and effectively adaptation occurs is highly individual—a person must listen to their body. If comfortable during a run, the body is already adapting or has adapted.

Even after adaptation, it is important to monitor body temperature and fluid loss. The most common mistake according to Reinpõld is going for a short run of just 30–40 minutes without bringing water. If it is very hot outside, she recommends running in the morning, as the air often does not cool down enough by evening. When heading out for a run, one should wear a hat and bring sufficient water. A wet T-shirt also helps with cooling—some people remove their shirt while running, but that is unwise because the sun then directly heats the skin, making it harder to cool down. A wet T-shirt cools the body much better.

A pleasant innovation is the appearance of drinking water taps along many cycling and pedestrian paths in Estonia—one can not only drink but also wet a hat. Such small details play an important role in how a person feels after a run. How to tell if someone is already overheating? Often the pace is low and pulse is normal, but the body simply does not allow continued exertion—symptoms include weakness, thirst, dizziness, headache, and nausea. If feeling worse, it is better to switch to walking, drink water, cool down, and seek shade. Most importantly, trust your own sensations. Reinpõld also advises paying attention to the condition of fellow runners—if their speech or behavior becomes strange, it may indicate overheating.