- The optimum temperature for a fast marathon is about 54 degrees.
- Running times slow by one minute or more with every seven degrees above that, because it becomes more difficult for the body to cool itself.
- When it is humid, sweat does not easily evaporate, so the body sweats even more. Blood volume drops, and the body has to make a choice: divert blood to the skin for cooling or divert it to the muscles for performance. It sends blood to the skin. With less blood going to the muscles, the runner slows down or stops. The challenge, then, is to find the fastest pace that can be maintained for 26 miles.
I am looking forward to my 10 km run this afternoon in sweltering heat again!