The effect of short duration static stretching and reinnervation on the recovery of denervated soleus muscle in the rat.

Denervation elicits profound alterations in the morphometry of the skeletal muscle. There is evidence that the increased mechanical load placed upon the muscle via rhythmic stretching attenuates denervation induced alterations in muscle morphology. To investigate the effect of short duration static stretching (40 min/day) for denervated and reinnervated muscle, a histochemical study was performed on the soleus muscle of the rat. Twenty-one eight-week-old female Wistar rats were used. Partial denervation was carried out by locally freezing the proximal root of the sciatic nerve innervating the soleus muscle. Contralateral hindlimbs were untreated and served as control. Axonal degeneration was evident within the sciatic nerve following freezing, although variable amounts of damage were observed and thin nerve fibers were observed at 3 weeks. No clear difference of morphological change of the sciatic nerve was observed in the short duration static stretching groups (group S) or the non-stretching groups (group D). The wet weight of the denervated soleus muscles progressively declined to a minimum at 2 weeks after injury (group D, 50.8 ± 8.9%; group S, 61.3 ± 4.2%) and began to reverse in the following 3 weeks. Muscle wet weight for short duration static stretching groups similarly decreased and began to reverse in the following 3 weeks. The muscle fiber cross-sectional area also similarly changed with the muscle wet weight. The type II fiber ratios of the denervated sides were consistently higher than the control levels. In non-stretching groups, type II fibers had increased by 3 weeks after denervation (49.4%), whereas type II fiber ratios of the short duration static stretching groups decreased after 3 weeks (31.3%). These data suggests that mechanical stimuli provided by short duration static stretching can prevent the atrophy of the denervated muscle over a short period. In addition, it was indicated that short duration static stretching affected the reinnervated muscle fiber type composition. However, the reinnervation took the crucial role of recovering from the atrophy and composing the integrity of the soleus muscles.