How to adjust your pace when it's hot?

With the heat setting in, continuing to train requires adaptation. Running in the heat is not just a matter of comfort: there is also, and above all, a physiological dimension that should not be overlooked. When the temperature rises, and even more so when humidity sets in, the body must arbitrate between performance and maintaining body temperature. Better understanding these physiological adaptation mechanisms allows us to accept adjusting our pace downwards, and above all to reduce health risks.

Why does heat change the rules of the game?

During an effort like running, the body produces heat. To maintain a stable internal temperature of around 37°C, it uses sweating and evaporation. But this system has its limits.

When it's hot, and even more so when the air is humid, sweat doesn't evaporate well. The more the heat and humidity factors intensify, the harder it is to reduce body temperature. The result: heat accumulates. The heart has to increase its output to help with thermoregulation, which leads to a higher heart rate… for an identical pace.

This is called cardiac drift: at a constant effort, heart rate gradually increases, even if you're not running faster.

Why is it necessary to slow down?