Factors affecting cold acclimation and thermogenesis in man.

Three types of cold exposure are observed in man: systemic moderate cold (SM), systemic severe cold (SS), and local severe cold (LS). Contrary to rat, prolonged exposure to SM cold does not produce non-shivering thermogenesis, as it does in the rat, possibly because of lack of active brown adipose tissue. Instead there is a reduction in heat production, in shivering, and in discomfort through a process known as habituation. No adaptation was found with exposure to SS cold, since shivering and discomfort always prevail and there is indirect evidence of enhanced sympathetic response after repeated exposure to SS cold. Exposure to LS cold leads to adaptive responses in which discomfort and autonomic activity are reduced. It is suggested that LS adaptation is also related to habituation.