Running and Thermal Physics

Posted by Paul A. Heckert Jun 10, 2008

I just finished my daily run. I didn't get moving as early as I should have this morning, so it was about 90 degrees F by the time I finished. With the heat wave in the eastern US, it is difficult to run or do other outdoor exercise.

The reason hot weather exercise is so difficult boils down to basic physics, specifically the laws of thermodynamics. The first law of thermodynamics says energy is conserved. It can change form but can not just disappear. The second law of thermodynamics says that no machine or process can be 100% efficient. There is waste energy which is converted to heat.

Applying these ideas to the exercising or working human body tells us that muscular processes are less than 100% efficient. Working or exercising muscles generate waste heat. In the winter this warms us to the point that it is possible to run through snow wearing shorts. In the summer the waste heat makes it difficult to keep our bodies cool while exercising. Therefore basic physics means that runners and other outdoor exercisers have a difficult time cooling their bodies.

If like me you run or do other outdoor exercise in hot weather, familiarize yourself with the symptoms of heat stroke and take precautions to keep your body cool. You can't violate the laws of physics.