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Exercising In the Heat


It’s summertime and you head out for a run. Before you even finish the first mile, your body feels as though it might ignite from the heat. It’s not your imagination. Fifteen minutes into your run and your body temperature could be as high as 5° F above normal. If you were to continue at this pace, fatigue and heat illness would no doubt take over.

The above scenario doesn’t have to happen. Drinking enough fluid, whether it be water or a sports drink, is imperative for exercising in hot or humid weather. Maintenance of body fluids is essential to maintaining proper body temperature. Sweat dispels heat through your skin. If you let your body become dehydrated, you’ll find it much more difficult to perform even the lightest of workouts. But don’t wait until you’re thirsty to start replenishing those fluids. Chances are, by the time you actually feel thirsty, your body is well on its way to becoming severely dehydrated. The following strategies will help you protect yourself from the onset of heat illness:

1. Hydration
Fluid replenishment before, during and after exercise is essential to avoid progressive dehydration. Always consume more fluids than you think you need before and after exercise, and strive to drink 6 to 8 ounces of fluid every 15 to 20 minutes during exercise.

2. Exercise
Intensity You should probably reduce the intensity of your workout, particularly the first few times you are exposed to higher temperatures.

3. Temperature
Use a heat stress index table to determine the risk of exercising at various combinations of temperature and humidity. While a 90° F outdoor temp is relatively safe at 10 percent humidity, the heat stress of 90° F at 50 percent humidity is the equivalent of 96° F. When the heat stress index rises above 90° F, you may want to consider postponing your exercise session until later in the day. Or, plan ahead, and beat the day’s heat by working out early in the morning.

4. Fitness
Physical training and heat acclimation can increase your blood volume, helping to regulate body temperature more effectively. Interestingly, the acclimatization process can be completed in seven to 14 days of repeated heat exposure. However, you must always continue to drink fluids before, during and after exercise.

5. Clothing
Wear minimal clothing to provide greater skin surface area for heat dissipation. Your clothing should be lightweight, loose fitting, light colored to reflect the sun’s rays, and of a material that absorbs water, such as cotton.

6. Rest
Know when to say “no” to exercise. Using common sense is your best bet for preventing heat stress when Mother Nature turns up the heat.

Compliments of: The American Council of Exercise

Reprinted with permission from the American Council on Exercise.

If you are interested in information on other health and fitness related topics, contact American Council on Exercise 4851 Paramount Drive, San Diego, CA. 92123; or go online at and access the complete list of ACE Fitfacts.