Chapter 59

Introduction

There are only three real sports: bullfighting, motor racing, and mountaineering. All the others are merely games.

Commonly attributed to Ernest Hemingway

The five primary areas of focus in the first half of this chapter are:

• a brief review of thermoregulation—how the body generates heat and how heat is lost

• strategies for measuring body temperature—a key to clinical assessment

• how hypothermia affects major body systems

• management of hypothermia and its complication, frostbite

• prevention of cold injuries.

The second half of this chapter focuses on exercise at altitude.

Generation of body heat

Humans function optimally in a relatively narrow temperature range. At ambient air temperatures above 28°C (82°F), heat produced by basal metabolism maintains the core temperature at 37°C (99°F). In conditions below this temperature, the body must produce additional heat to remain thermoneutral. Such heat production can be achieved by greater physical activity and autonomically mediated shivering, a physiological response of healthy individuals in a moderate environment.

Shivering involves involuntary muscular contractions in response to cold and uses energy stores quickly. The capacity to shiver lessens as local glycogen stores are depleted. The intensity of shivering is generally related to the rate of change of temperature. Shivering results in decreased muscular coordination and, therefore, impairs sporting performance. Non-shivering thermogenesis occurs in young children because of metabolism of brown fat; however, this mechanism is not available to adults.

Heat loss

Heat transfer occurs mainly from the skin and is therefore regulated by the circulation, the amount of insulation, and perspiration. Heat loss occurs through conduction, convection, radiation, and evaporation.

Conduction occurs because of direct contact with a cold object or air. Heat transfer is related to the area of contact and the relative heat conductance of the objects. Conduction is most important in water immersion, as the conductivity of water is approximately 23 times that of air. Conduction may also be important when lying on cold, wet ground.

Convection relates to the movement of air close to the body. Convection becomes important in windy conditions with temperatures up to 20°C (68°F). It is also significant in sports such as cycling and running.

Radiation involves the emission of heat energy to nearby objects. This occurs from uncovered skin and is the greatest source of heat loss under normal conditions. In cold conditions, however, the amount of heat loss through radiation is less as the skin temperature approximates the environmental temperature.

Heat lost as sweat on the external skin or clothing is converted from liquid to gas by evaporation. Evaporation forms part of the body’s insensible water losses. Evaporation is increased in dry, windy conditions and may go unnoticed. Heat is also lost through feces, urine, and respiration.

Minimizing heat loss

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