Physiologic Systems and Their Responses to Conditions of Heat and Cold.

摘要

Individuals exercise and work in a wide range of environmental conditions. Depending on environmental conditions and a person's metabolic rate and clothing, exercise can accentuate heat gain or heat loss, causing body temperature to rise or fall. Healthy humans normally regulate body (core) temperatures near 37 deg. C at rest, and with environmental and/or exercise perturbations, body temperatures can fluctuate between 35 deg. C and 41 deg. C without adverse health consequences. Fluctuations outside that range can be associated with morbidity and mortality. In this chapter, the term exercise refers to dynamic exercise, and training refers to repeated days of exercise in a specific modality leading to adaptations. The term stress refers to environmental and/or exercise conditions that tend to influence the body's heat content, and strain refers to the physiologtc consequences of stress. The magnitude of stress and the resulting strain depend on a complex interaction among environmental factors (e.g., ambient conditions) and the individual's biologic characteristics (e.g. acclimatization status and body size) and activity level (e.g., metabolic rate and duration). The term acclimatization refers to adaptations to both natural (acclimatization) and artificial (acclimation) environmental conditions. In this chapter, we examine the effects of both heat stress and cold stress on physiologic responses and exercise capabilities. Human thermoregulation during exercise is addressed, but more detailed reviews on this process during environmental stress can be found elsewhere. This chapter reviews the physiology. needs, and assessmem of human water and electrolyte balance. The extent to which water and electrolyte imbalances affect temperature regulation and exercise performance are also considered. This chapter includes information on the pathogenesis of exertional heat illness and hypothermia, since exercise can increase morbidity and mortality from thermal injury.