How to Run in Heat and Humidity

The New York Times reports that exercise physiologists have some new thoughts about how to prepare for running a marathon in places where the heat, humidity and pollution are off the charts scary–places like Osaka and Beijing. Cities like those are unlikely to offer the 54 degree days that have been shown to produce the fastest marathon times. For every seven degrees above that, the Times reports, running
times slow by one minute.
That’s because, according to David Martin, an exercise physiologist and a professor at Georgia State University, 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.
Ultimately, the Times’ experts offer three pieces of advice to runners who hope to prevail over heat, humidity and pollution.
1. Do not use lotions, including sunblock, because they add a barrier to the evaporation of sweat.
2. Try glycerin loading (explained somewhat on this page)
3. Parcel calorie intake evenly over the course of a day, rather than calorie-loading in the evening.