Detraining of exercise-trained rats: effects on energetic efficiency and brown adipose tissue thermogenesis.

Complete energy balance measurements were made in exercise-trained (treadmill running) rats subjected to 27 d of exercise detraining. The 20% difference in body-weight that existed at the end of the training period between sedentary and trained rats was negated by detraining. Detrained rats had twice the body-weight gain of their untrained controls. An elevation (12%) in metabolizable energy (ME) intake (relative to body-weight) was observed in detrained rats while their gross energetic efficiency was augmented by 60%. Energy expenditure, excluding the estimated costs of fat and protein storage, was similar for detrained and untrained rats. Complementing the latter was the finding that thermogenesis in brown adipose tissue, a known energy buffering process, was also similar. Elevated ME intake (relative to body-weight) largely contributed to the increased energetic efficiency of detrained rats.