Energy conservation and exercise dependence: a sympathetic arousal hypothesis.

The present article reviews a wide range of studies which suggest that energy balance mechanisms are affected by food restriction and exercise training. Specifically, food restriction produces adaptive decreases in basal metabolic rate, a decrease in the energy utilized in the performance of a specific task, and an increase in the efficiency of food utilization following resumption of pre-restriction feeding patterns. Exercise training produces an adaptive decrease in the energy required to perform a specific task and in the hormonal output to a standard work task. Conflicting evidence exists on the combined effects of exercise and dieting on energy conservation. This energy balance information is used as the basis for the development of a sympathetic arousal hypothesis of exercise dependence. We propose that exercise dependence is mediated by adaptive reductions in sympathetic output to exercise tasks as a result of training, requiring the individual to engage in heightened levels of activity to produce pre-training levels of physiological arousal.