Beat the Heat

Beat the Heat By Barbara A. Brehmn, Ed.D.

When you're hot, and prudent exercisers take the summer weather into account when setting up their exercise programs. Hot weather provides two challenges: avoiding dehydration and preventing dangerous elevations in internal temperature.

When you exercise, your muscles generate heat.
Your circulatory system helps get rid of this excess heat by sending blood to the surface to release heat into the environment. People with fair skin will notice skin redness during and following exercise, especially in the face. That's a result of increased blood flow to the skin (unless it's a sunburn). The effectiveness of this method of heat release decreases as air temperature rises. Exercising with little or no air current also reduces the release of heat.

Heat may also be lost through the evaporation of sweat. Sweating is very effective when the air is dry, especially if there is a breeze. Hot, humid weather provides the biggest challenge to our cooling systems because heat is least effectively released to the environment.

Your risk of dehydration increases when you exercise in the heat. Dehydration is dangerous because if causes a decrease in blood volume. A lower blood volume means less circulation to the skin and possibly dangerous elevations in internal temperature.

There are many ways to beat the heat. Hot weather need not become an excuse to take a summer vacation from your exercise program. Following are a few suggestions for preventing heat stress and adapting your program to the demands of summer fun.

Drink plenty of fluids to prevent dehydration.
Exactly how much fluid you need to drink depends on your size, how much fluid your stomach can handle, your sweating rate and environmental conditions. Nutritionists generally recommend 2 to 3 cups of water two hours before exercising in hot weather, and then another 1 to 2 ups 15 minutes before your workout. During your workout, continue to drink about 1 cup every 15 to 20 minutes. Cool drinks (40 to 50 degrees) are absorbed more quickly tan lukewarm drinks.

Beware of early signs of dehydration.
Two good indicators of hydration are your body weight and urine output. Any weight lost during a workout is due to fluid loss. Weigh yourself before and after exercise, and drink the difference, about 2 cups every pound. Monitor the volume and color of your urine. A pale color indicates normal water balance.

Recognize symptoms of heat illness.
Thirst, tiredness, disorientation and visual disturbances can all point to heat illness. Stop exercising, drink something and find a cool place to rest. More drastic symptoms of heat exhaustion include a rapid, weak pulse, headaches, dizziness and general weakness, and may require medical attention.

Consider environmental factors.
When deciding whether you should exercise outdoors, take all environmental factors into account, including temperature, humidity, the intensity of the sun and how much the air is moving. Temperature alone does not tell the whole story. Heat stroke deaths have occurred during exercise in temperatures below 75 degrees when the relative humidity was very high. Be creative. An air-conditioned fitness center is one answer. But getting outdoors is fun, too. Find a shadier walking route, go out early or late in the day, or exercise in the water. Several factors affect heat tolerance, including body composition, fitness level and exposure.

Body composition.
Fat acts as insulation and slows heat loss to the environment, reducing heat tolerance. Larger people also expend more energy when performing a given amount of weight-bearing exercise, such as walking or aerobics. They, therefore, generate more muscle heat during such activities.

Fitness level.
If you are new to exercise, it may take you longer to get used to exercising in the heat. Take your time. Exercise will gradually get easier as you get in shape.

Exposure.
We become acclimatized to warmer weather after exercising in it for about two weeks. The circulatory system becomes better able to handle the increased demands of heat release, and we begin sweating earlier and more heavily.
Recognize your own heat tolerance. Monitor your heart rate and stay within your target zone. You will find your heart rate rises faster than usual in the heat. The ability to exercise safely in the heat varies considerably from person to person. It is important to know your own limits so that summer exercise is safe and fun.