Heat Adjustment Calculator

How heat affects your race

The optimal running temperature is around 50°F (10°C). Above that, your body diverts blood flow to the skin for cooling, reducing the oxygen available to your muscles. By 80°F, most runners see a 10-15% pace slowdown. High humidity makes it worse because sweat can't evaporate efficiently, so your cooling system breaks down.

Heat doesn't just slow you down. It changes your fueling needs. You sweat more (requiring more fluid and sodium), your gut absorbs nutrients less efficiently, and gel tolerance often drops. At high temperatures, liquid calories become more practical than gels.