More warmer days are forecast, which makes this a timely question for those who enjoy running outdoors.

Winter running brings its own challenges, but even in Estonia, the summer months are not without their difficulties. Running in the cooler morning hours is the best practice, but how well you cope with the heat depends largely on whether you have trained your body to adapt to it, according to Tallinn University exercise physiology lecturer Karmen Reinpõld, who responded to a reader's question sent to ERR's Novaator portal.

"Running outdoors in hot weather is not bad in any way, if your body has adapted to it," Reinpõld noted. At the same time, any sudden appearance of hot weather in otherwise relatively cool Estonia can cause issues if a person has not previously conditioned themselves to run in such conditions. Overheating can occur not only due to the ambient heat and sunshine itself, but also because the muscles themselves generate a great deal of heat. "This can become dangerous for the body: When the core temperature rises too high, you start feeling unwell," she explained.

It is precisely for this reason that top athletes, such as cyclists ahead of the Tour de France, undergo specific acclimatisation training. For runners acclimating to the heat, one approach is to dress more warmly than they normally would during cooler weather, or to train indoors without cooling down. "The body then makes changes to its internal systems to adapt better and cool itself more effectively. For instance, it starts sweating sooner. That cools the body, allowing it to cope much better," Reinpõld said.

Everyone tolerates heat differently, so there is no specific temperature point beyond which people should or should not run. Conversely, some people perform noticeably worse in cooler weather, as their bodies become more sluggish. "When it gets warmer, even up to 25 degrees Celsius or more, they perform well without having to do anything special," Reinpõld added. Other people, however, begin to overheat already at temperatures of 20 degrees, and with temperatures above 30 degrees Celsius, the lecturer said, almost everyone is likely to struggle to varying extents, at least to begin with.

At the end of the day, anyone — including people from Estonia and other northerly climes — can train their body to cope with hot weather. This is particularly worthwhile for those planning to take part in the first running races of the spring. "Those who want to adapt can deliberately overdress a little, for example by wearing a thicker hat and gloves, as the head and limbs are otherwise very effective at releasing heat," Reinpõld advised. Caution is needed, however: this approach should not be used across the board or throughout an entire workout, particularly during more taxing sessions. Regular short periods of such training are preferable to fewer, longer stints, or no such training at all. Without that, the body will return to its so-called comfort zone, Reinpõld said. "How quickly or how well adaptation takes place is also highly individual. People have to listen to their own bodies," she noted. Fortunately, this is a relatively straightforward thing to do: if running feels comfortable, the body is already adapting or has adapted. In short, the expert said, it is never too late to start heat acclimatisation training, though it is never too soon either. "If we've done it three or four times a week, then after at least two weeks the signs of adaptation are already clearly visible," she noted.

Drink plenty of fluids and dampen your clothes

Even after getting fully acclimated, Reinpõld said, runners should still be careful to ensure they do not overheat or lose too much fluid during a run, and they still need to take on water or other fluids. "I think the most common mistake in running is that people head out for what they think is a short run, even if it's just 30 or 40 minutes, without taking any water with them," she cautioned. In genuinely hot running conditions, dehydration develops very quickly and you would need to rehydrate even within those time-frames.

In genuinely hot weather, Reinpõld recommends running in the morning. This is preferable even to the evenings, when the heat has effectively accumulated through the day and temperatures often have not yet fallen back down again. Before heading out, runners should always wear a cap or other head covering and take enough fluids with them. Dampening your running top before the run is also an effective way to prevent overheating, and is preferable to running without a t-shirt. "Sometimes we see people taking their shirts off, but that's not sensible because the sun heats the skin more directly and cooling actually gets more difficult. A wet shirt cools the body much more effectively," Reinpõld said.

One welcome development in the cooling down department, Reinpõld noted, is the growing availability of water fountains along recreational pathways. These allow runners not only to drink but also, for example, to wet their caps or anything else. "Small things like these can make a huge difference to how good you feel when you return from a run," she added.

Pay attention to others as well as yourself

When looking out for signs of overheating or dehydration on a hot day, it is important to pay attention to other runners, as well as oneself. But how can you tell when someone has pushed themselves too hard while running on a hot day? "If we're with someone who is pushing themselves and their speech or behaviour starts becoming a little unusual, that may indicate they're overheating," Reinpõld said.

As for one's own well-being: "Often the pace is low enough and the heart rate isn't particularly high, but the body simply won't let you push any harder," Reinpõld described. "This is the first sign that overheating symptoms are approaching: weakness, thirst, dizziness, headache and nausea begin to appear." It is wiser to break into a walk instead of continuing to push yourself to run in such cases. It is vital to drink, cool yourself down and move into the shade if you continue to feel below par. "If your brain starts telling you, figuratively speaking, that it won't let you go any farther, you should definitely slow down, walk and see what happens next," Reinpõld said.

Ultimately, the most important thing while running is to trust your own feelings and judgment, including if you start getting to a stage where sound judgment faculties themselves are at risk. "If the situation gets confusing and you can't tell what's happening, it's sensible to state you should hold back," Reinpõld noted. The Tallinn Marathon and its supporting events take place in September, meaning serious entrants have to train through summer in any case.

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