Effects of short duration static stretching on the denervated and reinnervated soleus muscle morphology in the rat.

Abstract

To investigate the effect of short duration static stretching of denervated and reinnervated muscle using a histochemical study on the soleus muscle of the rat. Prospective randomized trial. University medical school in Japan. Fifty-four 8-week-old female Wistar rats with a mean weight +/- standard deviation of 185.8+/-9.9g. After a cold injury was applied to the rat right sciatic nerve, the bilateral soleus muscles were maximally stretched in the dorsiflex posture of the ankle joints for 40 minutes a day, 6 times a week (group S). Rats were compared with nonstretched rats (group D) for up to 4 weeks. Main outcome measures Muscle fiber cross-sectional areas, muscle fiber types, and sciatic nerve morphology. No apparent difference in the morphologic changes of the sciatic nerve was found between groups D and S. The mean fiber size progressively declined to a minimum 2 weeks after the injury and reversed in the following weeks. At weeks 1 and 2, the mean type I fiber size in group S was significantly larger than in group D (P<.05). The number ratio of the type II to total fibers increased until 3 weeks in group D, whereas the ratio in group S was increased at 2 weeks, and successively decreased. The mechanical stimuli of static stretching could prevent atrophy of the type I fibers in the denervated muscle and affect the reinnervated muscle fiber-type composition.