Effects of exercise on energy balance in meal-fed mice

Abstract

The effects of exercise on energy balance have been investigated in mice accustomed to eating their daily food ration in three meals. A meal period lasts 1 hour, and during that period mice were allowed to eat unrestrictedly a pelleted stock diet. Two series of experiments were conducted. In one series of experiments indirect calorimetric measurements were carried out in untrained mice that were assigned to 3 experimental groups: a first group of mice was allowed to rest; a second group of mice was exercised immediately before one of the 3 meals; a third group of mice was exercised immediately after one of the 3 meals. The exercise bout consisted of 1 hour of forced exercise on a rodent treadmill at a speed of 20 meters per minute. O 2 consumption (VO 2) and CO 2 production were monitored throughout a full day except at the time the exercising animals were on the treadmill. In a second series of experiments long-term energy balance measurements were carried out. Mice were then assigned to experimental conditions similar to those previously described for 31 days during which period food intake and body weight were continuously monitored. At the end of 31 days of experiment, mice were killed, and their carcasses were individually analysed for their contents of energy, fat and protein. Carcass and food gross energy contents were assessed by bomb calorimetry. At the end of the long-term energy balance trial, the percentage of fat, the energy gain, the energy density and the weight of the dry carcass were significantly lower in exercised groups of mice than in the resting group of animals. There was no difference between groups in the carcass protein contents. Energy expenditure for the whole period of 31 days was significantly higher in mice that exercised postprandially than in mice allowed to rest. Incidentally, postprandial O 2 consumption was significantly higher in postprandially exercised mice than in resting animals. In postprandially exercised mice the final percentage of fat and the energy density of dry carcass were lower than those of preprandially exercised mice. The present results suggest that exercise in conjunction with meal eating may lead to an excess post-exercise energy expenditure capable of affecting long-term energy balance.