On race day, you may have the horsepower in your legs to get the 6.2 miles down Peachtree Road, but if your cooling system is not ready, your tow truck may become an ambulance and your mechanic may be a doctor at Grady.
Any machine, such as your body or car, takes in fuel (food or gas) and burns this to produce movement and heat. The food that you eat is quantitated in calories, which is a measurement of the heat produced when burned. For every calorie you use in running, 75% ends up as heat and only 25% as work energy in the most efficient athlete. As you exercise, the body must shed this extra heat. To do this, you have a cooling system that must be conditioned to be ready on RACE DAY.
One form of heat loss is accomplished by radiant transfer from your skin to the air. On cool days, this system works well. To lose heat on the hot/humid days of July 4th, your body must sweat. Blood and energy must be redirected away from the muscles used for running to the skin to produce sweat. Sweating is only successful in removing heat when the sweat turns to water vapor (evaporates) and takes heat with it. The sweat that drips or is wiped off is of little benefit in cooling. As the humidity (water vapor already in the air) increases, this evaporation of sweat becomes more difficult. The combination of high temperatures and high humidity we see on July 4th can be too much for the trained, but un-conditioned runner.
As the weather begins to get hotter and more humid, take some of your training runs in the warmer times of the day. You will need to run slower, but with repeated exposure over the next month you will stay cooler and safer on race day. Your ability to sweat becomes limited as your fluid level drops. Start your run well hydrated and take fluids as you run. Weigh yourself before and after a run in the heat. Each pound of weight loss is one pint of fluid you lost that was not replaced. Work now on keeping well volume loaded during your runs. Extra water splashed on your face and body functions as sweat as it evaporates and can be used as a helpful adjunct to cooling. Wear light colored loose fitting running clothes that expose as much of the skin to the air as possible to help with evaporation.
There must be a balance between heat generated with running and heat loss. Frequently on race day, the heat loss becomes the limiting factor. This heat is trapped in the body, causing increasing temperatures and the problems of heat exhaustion and heat stroke. Conditioning yourself now can reduce the likelihood of boiling over on race day.
–Dr. Joe Wilson
Runner since 1966
Medical Director since 1987
Cardiologist with Cardiology of Atlanta and St. Joseph’s Hospital