The effect of exercise on the utilization of dietary energy by the laboratory rat
The main purpose of this investigation was to examine the effect of enforced moderate exercise, in combination with various dietary regimes on the efficiency of energy storage, mobilization and utlization in the male Wistar rat. The experimental approach adopted was to combine the carrying out of energy balance studies using the body balance technique, feeding diets of determined metabolizable energy content, with more detailed work on energy expenditure involving the use of indirect respiration calorimetry. Animals subjected to daily enforced exercise (by swimming or treadmill running) gained weight more slowly, had lower final body weights and showed a significant reduction in body fat gain compared to sedentary controls. Fat-free dry weight was not affected by training. These effects were due to the increased energy expenditure associated with the imposed exercise and also, during the initial period of training, to a significant reduction in food intake. Neither exercise nor training affected the metabolizable energy content of the diets. Treadmill running but not swimming exercise potentiated the thermic response to food and this effect extended beyond the cessation of the exercise. Pre-exercise (anticipatory) and postexercise (recovery) metabolism contributed significantly to the energy expenditure associated with the imposed exercise tasks. Furthermore, trained rats exhibited an increased resting metabolic rate and thermic response to food. Also, in work involving lkC_glucose feedings they appeared to oxidize the exogenous substrate more rapidly than sedentary counterparts. Some of the observed metabolic adaptations to the trained state were modified by diet. These parameters included body fat gain, liver weight, liver glycogen levels, and concentrations of plasma metabolites (glucose, free fatty acids and triglycerides) during exercise. It is concluded that interactions between diet, exercise and metabolic adaptation to physical training can markedly affect the overall energy balance.
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