Why can’t I run as fast when it’s a humid day?

(Image by mainathlet from Pixabay)

Question from Colin Ennis

Increased humidity means that there is more moisture in the air, and less space for sweat to evaporate into. Sweating becomes less effective in cooling you down because the air is less capable of holding the extra moisture that evaporates from your sweat. You can’t run as fast because your body is trying to prevent you from overheating.

This excess moisture increases the temperature of your body, which in turn impacts the pace you can run at. Your body is putting more energy into adjusting its temperature, so it can’t use as much to power your muscles.


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