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OBJECTIVES

By studying this chapter, you should be able to do the following:

  1. Define the term homeotherm.

  2. Present an overview of heat balance during exercise.

  3. Discuss the concept of “core temperature.”

  4. List the principal means of involuntarily increasing heat production.

  5. Define the four processes by which the body can lose heat during exercise.

  6. Discuss the role of the preoptic-anterior hypothalamus as the body’s thermostat.

  7. Explain the thermal events that occur during exercise in both a cool/moderate and hot/humid environment.

  8. List the physiological adaptations that occur during acclimatization to heat.

  9. Describe the physiological responses to a cold environment.

  10. Discuss the physiological changes that occur in response to cold acclimatization.

OUTLINE

  • Overview of Heat Balance during Exercise 270

  • Temperature Measurement during Exercise 271

  • Overview of Heat Production/Heat Loss 272

    • Heat Production 272

    • Heat Loss 272

    • Heat Storage in the Body during Exercise 275

  • Body’s Thermostat—Preoptic-Anterior Hypothalamus 276

    • Shift in the Hypothalamic Thermostat Set Point Due to Fever 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

    • Physiological Responses to Exercise in the Cold 288

    • Cold Acclimation 289

KEY TERMS

acclimation

acclimatization

conduction

convection

evaporation

homeotherms

hyperthermia

hypothermia preoptic-anterior hypothalamus

radiation

specific heat

INTRODUCTION

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.

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 strategy of homeotherms uses ...

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