The hand in the cold, performance and risk.

When a person is exposed to cold and his metabolic rate is insufficient to maintain a positive or neutral heat balance, the body will cool down. For the extremities this will result in a drastic reduction of blood flow, resulting in a so called "physiological amputation" with extremity cooling towards ambient temperature. The dexterity decrease observed with cold extremities is most likely caused by cooling of muscles and joints, and not by effects on receptors, nerve conduction or central effects. It is shown, that dexterity decreases can be described in terms of wind chill equivalent temperature and exposure time for a certain clothing and work configuration. Further, the risk of skin freezing and reduced dexterity due to touching cold objects can be described using the contact coefficient of the respective material and the contact time. This risk is modulated by metabolic rate and hand protection (gloves). Gloves drastically reduce cooling speed and freezing risk, but they also cause increased risks due to reduced dexterity due to glove thickness. For a general description of performance and risk of hand cold exposure in relation to climate and exposure time more data are needed.