Running a fast marathon

From a story in The New York Times:

The overwhelming challenge, the group (of runners, coaches and scientists) agreed, was to run well in high heat and humidity. Dr. Martin, analyzing performance records for men, calculated that the optimum temperature for a fast marathon was about 54 degrees (12 celcius). Running times, he said, 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.

The result is predictable, Dr. Martin said. 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. Go too fast and you may collapse before the race is over. Go a little slower than you have to and you may lose the race.