The hotter it is, the slower you run—but humidity plays a role too.
When the air is full of moisture, sweating doesn t cool you down like it usually would.
You won t be able to run as fast, because your body is trying to prevent you from overheating.
A chart from Runners Connect attempts to nail the effects of humidity down to a number.
This is only approximate, since the way you overheat also depends on other factors like your body size and shape the bigger you are, the easier it is to overheat and whether you re already used to exercising in the heat.
To find it, plug in today s temperature and percent humidity into this dew point calculator.