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why does body temperature increase after exercise

Vigorous exercise boosts your body's heat production and can increase your body temperature by several degrees. Your working muscles are responsible for the increase in heat production, but your body's ability to retain or dissipate heat and your external environment also play a role in how high your core temperature rises during your workout. To work, your muscles need energy, which they obtain by burning fuels such as fats and carbohydrates in a series of chemical reactions that produce heat. As your muscles warm up during your workout, blood circulating through the muscles is also warmed, producing a rise in core temperature. The amount of heat your muscles produce is related to the amount of work they perform. The more strenuous your workout, the more heat they produce. During very vigorous workouts, muscle heat production can increase 15 to 20 times above resting levels. How high your temperature rises during your workout depends not only on how much heat your muscles produce, but also on how fast your body loses heat. In cold conditions, your body loses heat rapidly. In hot, humid weather, your body is less able to dissipate excess heat, making overheating more of a risk. A rise in core temperature to above 104 degrees Fahrenheit can result in life-threatening heat stroke, so your body has a number of mechanisms to keep your core temperature within fairly narrow limits, even during a strenuous workout.

As your core temperature increases during your workout, blood is shunted away from your core to your skin, which allows your skin to radiate more heat, reducing your temperature. Sweating also helps to cool you. As sweat evaporates, it carries off excess heat. Because less sweat evaporates when the humidity is high, you're more likely to overheat in muggy weather than in dry conditions. As you become more fit with training, your body's ability to dissipate heat improves, a process called acclimatization. You begin sweating earlier in your workout, and at a lower temperature. If your core temperature rises above 104 degrees Fahrenheit, you're at risk for heat stroke, a potentially fatal condition that damages multiple body systems. To prevent the risk of heat-related illness during exercise, the American College of Sports Medicine recommends avoiding strenuous exercise during hot, humid weather, wearing light clothing and avoiding dehydration by drinking sufficient fluids before and during your workout.

Dehydration greatly adds to the risk of heat-related illness.
When you exercise, your muscle cells need to rapidly mobilize large amounts of glucose to provide energy. Only a quarter of this energy is actually converted to motion, however; the remainder is lost as heat. Your body employs a variety of mechanisms to rid itself of this excess heat, but body temperature can still rise slightly during prolonged exercise and drop slightly thereafter. While you exercise, blood vessels near the surface of your skin dilate and glands in your skin secrete sweat to help cool you down. Despite these measures, however, your body temperature can still rise by a couple of degrees Celsius before the rate of heat loss equals the rate of heat gain from metabolism. Occasionally, core temperature during exercise can rise to as high as 40 degrees Celsius or 104 degrees Fahrenheit, although this is more unusual. After you stop exercising, the rate at which your body produces heat decreases, while the mechanisms you use to dissipate heat remain in operation until your core temperature returns to its normal level. Your core temperature doesn't drop below normal levels, however, unless another health condition is involved. Normal resting core temperatures can range from 97. 7 to 99. 5 degrees Fahrenheit.

It may take a little time before elevated temperature during exercise returns to normal. A 2008 review in the journal "Annals of the Academy of Medicine, Singapore" described an experiment that illustrates how body temperature changes during and after exercise. Ten male recruits in the Singapore Armed Forces marched seven and a half miles carrying a heavy load, pausing twice during this period to rest. The average core temperature of the recruits rose from 99. 5 degrees at the start of the march to a little over 101 by the first rest period, then sank back to about 100 degrees F. When they started marching again, their average temperature rose to 102 before sinking back below 101 during the second rest period. The rate at which temperature falls after exercise may depend on ambient air temperature and other conditions. It's much easier for your body to lose heat, for example, if you're running in midwinter in North Dakota than it is in midsummer in Texas. It's also important to make sure you get enough water. Because your body is secreting sweat as a way to cool down, you can potentially become dehydrated if you lose too much water.

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