Physiological Systems and Their Responses to Conditions of Heat and Cold
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA THERMAL AND MOUNTAIN MEDICINE DIVISION
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Individuals exercise and work in a wide range of environmental conditions temperature, humidity, sun, wind, rain, other water Depending upon the environmental conditions, metabolic rate, and clothing, exercise can accentuate either heat gain or heat loss, causing body temperature to rise or fall. Humans normally regulate body core temperatures near 37 degrees C and fluctuations within the narrow range of 35 to 41 degrees C can degrade exercise performance. Fluctuations outside that range can be lethal. Therefore, heat or cold stress can have profound effects on exercise capability as well as 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. Throughout this chapter, stress refers to environmental exercise conditions tending to influence the bodys heat content and strain refers to physiological consequences of stress. The magnitude of stress and the resulting strain depends upon the complex interaction of environmental factors e.g. ambient conditions, clothing, the individuals biological characteristics e.g., acclimatization status, body size and exercise task e.g., metabolic rate, duration. Acclimatization refers to adaptations to both natural acclimatization and artificial acclimation environmental conditions. This chapter examines the effects of both heat stress and cold stress on physiological responses and exercise capabilities. Human thermoregulation during exercise is addressed, but more detailed reviews on human thermoregulation during environmental stress can be found elsewhere. This chapter includes information on pathogenesis of exertional heat illness and exertional hypothermia, since exercise can increase morbidity and mortality from thermal injury. In this chapter, the focus is on acute and chronic acclimatization environmental exposure.
- Anatomy and Physiology
- Stress Physiology