Influence of exercise on muscle fibers in rats with steroid myopathy.

The influence of mild exercise on skeletal muscle fibers was investigated histochemically to assess the effects of exercise on steroid myopathy and its efficacy for preventing this disease. Twenty male Wistar rats were divided into 4 groups of 5 each: group T, which received exercise alone; group S which received steroid alone; group ST which received both exercise and steroid; and group C, the control group. In groups S and ST, hydrocortisone was administered subcutaneously at a dose of 10 mg/kg/day for 4 weeks. In the exercise groups, the animals were made to run at a speed of 15 m/min for about 1 h/day for 5 days a week on a treadmill. After the completion of treadmill exercise and steroid administration for 4 weeks, the rats were anesthetized with Nembutal, the soleus muscle (SOL) and the extensor digitorum longus muscle (EDL) were removed and prepared for examinations. The area of type I fibers in the SOL was significantly larger in group ST than in group S. The area of type IIa fibers in the EDL was significantly larger in group ST than in group S. In group S, the proportion of type I fibers in the SOL was significantly lower than in the other three groups. There was little difference in fiber type distribution between groups ST and C. These results suggest that steroid myopathy can be prevented by even mild exercise.