The main aim of this study was to investigate the effect of an energy-restrictive, high-protein diet with or without exercise on muscle morphology and biochemistry. Moderately overweight postmenopausal women (49 to 58 yr, body mass index: 25 to 42 kg/m2) were randomly assigned to three groups for 12 wk of intervention; namely, a control group, a group on a 4.2 MJ/day diet, and a group on 4.2 MJ/day diet combined with aerobic and anaerobic exercise. Muscle morphology and biochemistry analysis were performed in 69 and 58 women, respectively. In contrast to the diet-only group, the die-plus- exercise group significantly increased the muscle fiber areas by 20 to 25%, the number of capillaries per muscle fiber type I by approximately 20%, and the activities of citrate synthase by approximately 35% and hexokinase by approximately 20% (p < 0.05). There were no statistically significant changes in any other muscle variable (p < 0.05). The respiratory exchange ratio decreased in both intervention groups by 2 to 4% (p < 0.01). It is concluded that 12-wk period of an energy-restrictive high-protein diet was not associated with major changes in muscle morphology or biochemistry. The addition of exercise to the die led to an adaptive increase in muscle fiber areas and in the oxidative capacity of the muscles.

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