The summer season is coming – at least in the northern emisphere – and this brings a lot of good things. Sunlight, warm weather, vacation and happiness for all.

Well, not all.

Runners are challenged in the warmer period of the year, since running in hot weather can be a very difficult, and potentially dangerous. On that regard, the human body does not work so differently than other machines. The process that converts energy (chemical, from our metabolic processes!) to mechanical (moving ahead) is far from being perfect.

Our motor has an efficiency lower than the engines moving our cars: about 80% of the energy is converted into heat. Yes, our carb fueled engine is not that efficient, after all. Although this is helpful in winter time (and the reason why we should wear less than if we were out walking), this becomes a problem when temperatures are going up.

There are several academic works on the topic. A study based on data from six of the major Marathons, found that most non-elite marathon runners performed best in temperatures around 7 °C (in all fairness, a bit cold for me). Another one focuses on Boston Marathon finishers, and sets the range optimal between 8 °C to 15 °C (that’s more me!). In general, all runners will lose performance with temperatures up, and this will become esponential with water content in the air, when the cooling processes become inefficient (consider this: when sweat drops, and is not evaporating from your body, its cooling power is lost!)

I want here to give few tips what to do (and don’t) when running in hot weather.

Drink and focus on hydratation

Quite obvious, but very important. Our main cooling process is the evaporation caused by sweating. This is why running in humid conditions is worse: the high content of moisture in the air reduces the evaporation rate. This makes difficult to cool down. But making sure to intake enough liquids to compensate the sweat loss is definitely rule number one!

Remember to rehydrate after the race, and compensate the loss of salts.

Wear appropriate clothes

Not only evaporation, but also radiation, convection and conduction help dissipating heat. Thermal convection is the mechanism when a hot surface is cooled down by a colder fluid (the air nearby). All these mechanisms have an effect greater when the exposed surface is higher.

Wear as little as possible, and avoid dark clothes (there are cool options in lighter colors, believe me). As many know, dark colors tend to absorb heat rather than reflect it. The choice of the right outfit is not only a matter of style, but has a primary importance here!

Plan accurately

I know, sometimes setting the alarm too early is annoying. Especially if on vacation. But temperatures in the early mornings can ve several degrees lower and this helps. Plus, if you are on the seaside, you can end your race dipping in the water when not so many are populating the beach. Well done!

Remember sunscreen!

Another advantage of focusing on early or late hours is the effect of the sun. But if you are planning a long run, it will be anyway something to take into account. To avoid unpleasant surprises, consider using sunscreen and wear sunglasses when you are going for your race!

Allow for adaptation

The body is able to adapt to many conditions, including running in hot temperatures. Our metabolic processes will progressively adapt: remember this and reduce your training load at the beginning, to adapt it progressively, listening to your body.

In general: be cautious

Running in warm or humid conditions is something to treat with the right caution. It is good to inform friends or family of your running path, going with some friends and, most importantly, listen your body and stop or slow down if needed.


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