Counteracting Cold and Windchill
The two most common and most effective ways for you to prevent cold injury and decrements in exercise performance resulting from cold are a limit the duration and severity of exposures to cold air or water and b insulate skin surfaces with clothing. Regarding the first option, you certainly should consult a windchill chart figure page to determine the risk of freezing your skin and appendages. You also should be alert for the onset of the clinical signs and symptoms of hypothermia table pagefrostbite, trench foot, and chilblains. You even may want to consider monitoring body temperature periodically to evaluate heat loss, especially if you are performing low-intensity exercise or if you rest for a prolonged period table page .
Regarding clothing, the insulation required to maintain body temperature varies in different environments and with different metabolic rates. The standard unit of clothing insulation is known as the Clo. One Clo is defined as the insulation necessary to maintain the comfort of a seated adult in a room that has a temperature ofF, rh or less, and air movement of m/min. Street clothing that is comfortable inF weather has a total Clo value of approximatelyFiguretop panel shows three activities seated clerical work, slow walking, strenuous power walking and environments that require insulation of Clo to maintain body temperature. As you can see, an increase of metabolic heat production allows thermal homeostasis at a lower environmental temperature, with Clo of insulation. Obviously, as exercise intensity and ambient windchill decrease, a greater amount of insulation is required. Figurebottom panel describes the different levels of clothing insulation required for six different metabolic rates see activities on diagonal lines. The unit of metabolic rate in this figure is known as Met. It is equivalent to approximately kcal/h in a large person, or kcal/h per square meter of surface area.
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Specifically, laborers and athletes should wear multiple layers of light, loose-fitting clothing that insulate the skin with trapped air. An outer garment that provides protection from wind and rain, and allows moisture to escape, is ideal. Breathable fabrics such as Gore-Tex are ideal for this purpose. Nylon parkas offer protection against severe windchill, but may not offer thermal insulation. Wool and polyester fabrics usually worn as inner layers retain some insulative value when wet, but cotton and goose down do not. The layer of fabric that lies in contact with the body ought to transport sweat away from the skin and not retain it. Polypropylene clothing wicks moisture away from the skin, in contrast to cotton fabrics, which retain
Activity levels also should be considered when selecting the proper layers of clothing. During immobilization or during low-intensity exercise bobsled, luge, driving a vehicle, one or two middle layers may be necessary. During high-intensity activities running, shoveling snow the outer layer or head covering may be opened or removed for brief periods to prevent excessive heat storage and sweat accumulation.