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By studying this chapter, you should be able to do the following:
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Define the term homeotherm.
Present an overview of heat balance during exercise.
Discuss the concept of “core temperature.”
List the principal means of involuntarily increasing heat production.
Define the four processes by which the body can lose heat during exercise.
Discuss the role of the preoptic-anterior hypothalamus as the body’s thermostat.
Explain the thermal events that occur during exercise in both a cool/moderate and hot/humid environment.
List the physiological adaptations that occur during acclimatization to heat.
Describe the physiological responses to a cold environment.
Discuss the physiological changes that occur in response to cold acclimatization.
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Overview of Heat Balance during Exercise 270
Temperature Measurement during Exercise 271
Overview of Heat Production/Heat Loss 272
Body’s Thermostat—Preoptic-Anterior Hypothalamus 276
Thermal Events during Exercise 277
Heat Index—A Measure of How Hot It Feels 279
Exercise in a Hot Environment 279
Sweat Rates during Exercise 279
Exercise Performance Is Impaired in a Hot Environment 279
Gender and Age Differences in Thermoregulation 283
Heat Acclimation 284
Loss of Acclimation 286
Exercise in a Cold Environment 287
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hypothermia preoptic-anterior hypothalamus
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Body core temperature regulation is critical because cellular structures and metabolic pathways are affected by temperature. For example, enzymes that regulate metabolic pathways are greatly influenced by temperature changes. Indeed, an increase in body temperature above 45°C (normal core temperature is approximately 37°C) can alter the normal structure of enzymes, resulting in the inability to produce cellular energy (i.e., ATP). Ultimately, an inability to produce cellular energy would result in cell death and eventually death to the organism. Further, a decrease in body temperature below 34°C causes a slowed metabolism and abnormal cardiac function (arrhythmias), which can also lead to death. Hence, people and warm-blooded animals live their entire lives only a few degrees from their thermal death point. Therefore, it is clear that body temperature must be carefully regulated.
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Humans and other animals that maintain a rather constant body core temperature are called homeotherms. The maintenance of a constant body temperature requires that heat loss must match the rate of heat production. To accomplish thermal regulation, the body is well equipped with both nervous and hormonal mechanisms that regulate metabolic rate as well as the amount of heat loss in response to body temperature changes. The temperature-maintenance ...