THERMOGENESIS DUE TO EXERCISE AND COLD IN WARM- AND COLD-ACCLIMATED RATS

Abstract

In both warm- and cold-acclimated rats, heat production was measured while the animals were at rest and running at maximum sustained effort at temperatures from 30 °C to those giving maximum thermogenesis. In both these groups, the maximum heat production during exercise did not exceed the maximum at rest in extreme cold. Exercise substituted for shivering in warm-acclimated rats and, at temperatures below 10 °C, resulted in hypothermia. Heat derived from exercise added to nonshivering thermogenesis in cold-acclimated rats above −20 °C. Below −20 °C, exercise substituted for shivering as in warm-acclimated rats at higher temperatures, and the rats became hypothermic. Extension of the temperature range for activity by cold acclimation appears to result from development of nonshivering thermogenesis, which, unlike shivering, is not eliminated by exercise.