Exercise during intermittent cold exposure prevents acclimation to cold rats.

1. Energy balance and brown adipose tissue growth were examined in four groups of male Wistar rats: (i) sedentary, living at 24 degrees C (warm), (ii) exercise‐trained, 2 h daily, living at 24 degrees C, (iii) living at 24 degrees C but exposed to ‐5 degrees C, 2 h daily and (iv) living at 24 degrees C but exercise‐trained while being exposed to ‐5 degrees C, 2 h daily. 2. Cold exposure during exercise training appeared to have little additional influence on body composition following 28 days of treatment; body mass gain, in addition to protein and fat gains, of exercised cold‐exposed rats were similar to the gains observed in exercised warm‐exposed control animals. However, in sedentary cold‐exposed rats protein, fat and body mass gains were significantly lower than the gains measured in sedentary rats not exposed to cold. 3. Metabolizable energy intake, expressed mass‐independently, was similar in sedentary warm‐exposed rats and both groups of animals that were exercise‐trained. Metabolizable energy intake was increased almost 15% in sedentary cold‐exposed rats. 4. Energy expenditure (mass independent), excluding the net cost of exercise training, was not different in sedentary warm‐exposed and exercised rats; energy expenditure was almost 20% higher in sedentary cold‐exposed rats. 5. Total protein and deoxyribonucleic acid (DNA) contents of brown adipose tissue were more than doubled in sedentary rats exposed to cold; protein and DNA levels were similar among the other three groups of rats. 6. Treadmill running during daily, 2 h exposure at ‐5 degrees C appears to prevent the cold acclimation responses that occur in sedentary rats receiving similar cold exposure.