Wind increases convective heat loss from the body surface (Santee and Gonzalez, 1988), thus providing the basis for the concept of wind chill (Siple and Passel, 1945). In humans exposed to environments colder than body temperature, heat flows from the body core toward the environment, primarily via dry (i.e., conductive and convective) heat-loss mechanisms. The biophysics of human thermal balance is considered in detail elsewhere (Santee and Gonzalez, 1988). The sum of these processes is heat storage ( S), which represents heat gain by the body if positive or heat loss from the body if negative. 2 Heat exchange between the body and environment occurs via evaporation ( E), radiation ( R), convection ( C), and conduction ( K), with W/m 2 being watts per square meter. Where M represents metabolic heat production, and W k represents energy leaving (positive for concentric work) or entering (negative for eccentric work) the body as external work.
The purpose is to provide a basis for considering how physiological responses influence performance and nutritional requirements of soldiers exposed to cold. This chapter reviews the human physiological responses elicited by cold exposure and then considers some factors accounting for differences in response among individuals. Besides protecting against cold effects and playing a role in the etiology of cold injuries, these physiological responses may alter the metabolism of persons living and working in cold climates. However, when behavioral strategies are inadequate to defend body temperature homeostasis, physiological responses are elicited. That is, they wear clothing, remain in shelters, and use various heat-generating devices. Humans tend to rely on behavioral thermoregulation to protect themselves against the cold. Currently, cold injury prevention is an area of major command emphasis for Army units operating in cold climates. Another 10,000 casualties resulting from cold injury occurred during the Korean War. German Army cold-injury casualties were at least as high. Army and Army Air Force casualties during World War II were attributable to cold injury. Throughout history, there are many examples of the terrible effects experienced by soldiers during military operations conducted during cold weather. Understanding and ameliorating the effects of cold is an important military concern.
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