ABC of sports medicine. Temperature and performance. I: Cold.

Abstract

Environmental temperature may cause problems through being either too cold or too hot; and the effects may be general, local, or secondary. These effects range from impairment of performance through injury or illness to possible death, either directly or indirectly. The effects of extreme cold in sport are more prevalent than are the results of extreme heat. For instance, for most sports in the world one of the numerically greatest hazards of cold is torn muscles or tendons. Hypothermia is also more common in Britain than is heatstroke. At milder degrees, cold can result in illness, injury, and death, whereas heat generally merely affects performance. The body normally maintains a steady deep (core) temperature of 37°C, though the set point changes during the circadian rhythm, after sleep loss, during hypobaria (at altitude), and after dehydration. This stability is achieved by balancing the rate of heat production (mainly from metabolic heat generation) with the rate of heat loss and also by altering the temperature of the superficial tissues (shell). The size of the shell also varies. Heat transfer to and from the body follows the normal rules of thermodynamics. The rate of dry heat loss (convection and conduction) depends on the temperature difference between the skin and the environment. The rate of evaporative heat loss (surface evaporation and through breathing) depends on the ambient humidity. Air movement (air over the body or the body through the air) increases both types of heat loss. Rough relation of core temperatures and shell sizes. (Note the arbitrary temperature definition of hypothermia (<35°C) and the range of shell sizes in normothermia.) When estimating the severity of cold stress - that is, the rate of heat loss - wind and wet are as important as temperature. A body is in fact losing more heat at +10°C …