Exercising in the Heat

Hyperthermia can take the fun and health out of summer exercise.

Hot weather exercising can do more than make you hot, tired and thirsty. Many of us remember the gruesome sight of Andersen-Schiess stumbling to the marathon finish line in the 1984 Los Angeles Olympics, suffering from hyperthermia.

Serious heat illness is even more likely to strike those who push their endurance and are not as well conditioned as Olympic marathoners.

Exercising in warm weather is safe if you know how to manage your exercise program and adjust your workout to the conditions.

While exercising you are exposed to both external and internal heat. External heat comes from the combination of environmental temperature and humidity - the heat index.

Humidity increases the effect of heat by limiting the effectiveness of sweat evaporation to cool you. Heat radiation from certain surfaces such as pavement, concrete or sand may make you feel hotter.

During intense exercise, muscle activity increases internal heat production 15 to 20 times more than at resting levels. Exercise intensity and duration, body size and shape, fitness level, acclimatization, state of hydration and type and color of clothing also affect internal heat production.

The body's "thermostat," located in the hypothalamus of the brain, senses any rise in body temperature and sends signals to dilate sufface blood vessels, increase respiratory rate and begin sweating. About 85 percent of heat loss is caused by the evaporation of sweat. Adequate hydration is the key to your body's ability to cool itself by sweating.

Heat illness occurs when the body produces more heat than it can dissipate. Most often this happens when dehydration accompanies excessive heat production.

Severity progresses as described below; from the mild stages of heat cramps and heat fatigue through more serious heat exhaustion to heat stroke, which can be fatal. See the next page for description of the various stages of heat illness.

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Foreword: Billie Jean King

Comments by Barb Harris
Editor in Chief,
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