TEMPERATURE REGULATION WHEN RUNNING IN THE COLD
The essential problem encountered during hot-weather running is the dissipation of sufficient heat to prevent heat storage and a dangerous rise in body temperature. When running in extreme cold, the critical danger is that the rate of heat loss from the body may exceed the rate of body heat production, causing the body temperature to fall. Once the temperature falls below 35 °C, mental functioning is impaired and the blood pressure falls. Below 33 °C, mental confusion develops and the limb muscles become rigid and immobile. Unconsciousness develops shortly thereafter, which leads to death from hypothermia if the body is not rapidly re warmed.
As Roald Amundsen, the first man to reach the South Pole, noted, the exercising body is a furnace (Huntford, 1985) so that with appropriate clothing, the human can survive even under the most unfavorable environmental conditions. Only under certain well-defined conditions does the rate of heat loss from the body exceed its rate of production during exercise, thereby leading to hypothermia.
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Survival in severe environmental conditions is, however, critically dependent on the choice of appropriate clothing, because despite its ability to produce an enormous amount of heat during exercise, the body has a relatively limited ability to reduce its rate of energy transfer to the environment. Thus avoiding hypothermia when exposed to the cold depends on two important factors: the choice of appropriate clothing and the maintenance of a high rate of heat production, as occurs during exercise. As described earlier, the insulating qualities of different clothes are rated in CLO units. At an environmental temperature of 50 °C, a resting human would need to wear 12 CLO units of clothing to maintain body temperature (see Exercises 4.2a), whereas a person running at 16 km/hr in the same conditions would be adequately protected by only 1.25 CLO units of clothing. Allowance must also be made for clothing that becomes wet; the insulating properties of clothing are greatly reduced when they become wet, because unlike air, water is a very poor insulator (i.e, a good conductor of heat). This explains why exposure to cold water (less than 10 °C) can induce hypothermia in lean swimmers within less than 30 minutes.
We can predict that hypothermia is likely to occur during exercise in those who either start exercising in clothing that is inappropriate for the environmental conditions or who dress in clothing that is appropriate for high rates of energy expenditure but which becomes inappropriate as the subjects become tired and slow down, thereby reducing their rates of energy expenditure. Hypothermia is also likely to affect those whose clothing becomes wet.
Hypothermia usually develops as a consequence of all these mechanisms acting in fatal concert (Pugh, 1966, 1967b). Maintenance of body temperature during exercise in the cold, therefore, depends on choosing clothing that is appropriate
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