American Council on Exercise by American Council on Exercise

It’s summertime and many people are taking advantage of the warm weather by running outdoors. But, unfortunately, the heat may beat them before they have the chance to finish the first mile. Only fifteen minutes into a run, a person’s body temperature could be as high as 5° F above normal and continuing could bring on fatigue and heat illness.

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 skin. If people let their bodies become dehydrated, it will be much more difficult to perform even the lightest of workouts. But people shouldn’t wait until they’re thirsty to start replenishing those fluids. Chances are, by the time they’re actually thirsty, their bodies are well on their way to becoming severely dehydrated. We recommend the following strategies to help prevent 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

Reduce the intensity of your workout, especially the first few times you are exposed to higher temperatures.

3. Temperature

Use the 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. 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.