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What causes the body to overheat when exercising in hot environments?

At rest, the body is able to balance heat production and heat loss so that it's temperature remains around 98o F. However, during exercise body temperature begins to rise as it converts the chemical energy from food into the mechanical energy necessary for movement. The degree of increase is directly proportional to the intensity of the exercise bout. In other words, the harder you are exercising, the higher your body temperature becomes. When you exercise in average indoor or outdoor conditions, the body is usually able to adjust quite well with this increase in body temperature. However, during hot conditions the body loses its ability to radiate heat from its surface. In fact, when the air temperature exceeds body temperature (above 98o F), the body actually gains heat from the environment. In this case, evaporation, or the conversion of a liquid (sweat) to a gas, becomes the body's only legitimate defense against overheating. Millions of sweat glands on the surface of the skin secrete large amounts of liquid, which when evaporated, help to cool the skin, which in turn cools the blood and ultimately the body. Serious problems can arise because high air temperatures stimulate excessively large amounts of sweat production, which if not replaced, can lead to a dehydrated state. Dehydration leads to higher body temperature. Severely dehydrated individuals can suffer circulatory collapse and death can occur.

Stephen D. Ball, Ph.D., Associate Professor, Nutritional Sciences, College of Human Environmental Sciences, University of Missouri Extension







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