Article
Effects of short duration static stretching on the denervated and reinnervated soleus muscle morphology in the rat1,

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Abstract

Sakakima H, Yoshida Y. Effects of short duration static stretching on the denervated and reinnervated soleus muscle morphology in the rat. Arch Phys Med Rehabil 2003;84:1339–42.

Objective

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.

Design

Prospective randomized trial.

Setting

University medical school in Japan.

Animals

Fifty-four 8-week-old female Wistar rats with a mean weight ± standard deviation of 185.8±9.9g.

Interventions

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.

Results

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.

Conclusions

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.

Section snippets

Animals and experimental protocols

Fifty-four 8-week-old female Wistar ratsa with a mean weight ± standard deviation (SD) of 185.8±9.9g were used. The following experimental protocol was approved by the ethics board of the Institute of Laboratory Animal Sciences of Kagoshima University. The rats were anesthetized by an intraperitoneal injection of sodium pentobarbital (50mg/kg). The skin covering the right buttock was cut, and the right sciatic nerve was isolated. The nerve was frozen and thawed several times by contact with a

Results

After the nerve freezing, the rats were ambulatory and dragged the foot of the frozen side. Loss of active movement in the ankle and toe joints was noted. The paralysis was alleviated, and voluntary extension of digits was noticed about 3 weeks after the operation. No apparent difference was seen in activity between groups D and S.

The distance between the proximal margin of the lesion and the entrance of the sciatic nerve into the soleus muscle was 20.1±1.7mm in group D and 20.0±1.2mm in group

Discussion

The mean fiber cross-sectional areas (fiber size) recovered 3 weeks after freezing. In this model, 70% of regenerated sciatic nerves reached the nerve terminal in the soleus muscles at 3 weeks and 100% reached that point at 4 weeks.10 It is estimated that it takes about 3 weeks for the sciatic nerve to traverse approximately 20mm to the soleus muscle, which is compatible with data reported previously.9, 10, 16

The denervation produced serious atrophy. In both the short duration static stretching

Conclusion

Denervation resulted in a reduction of fiber size and changes in fiber-type composition. The mechanical stimuli provided by short duration static stretching can delay the atrophy of type I fibers in the denervated muscle over a short period, and short-duration static stretching affect the reinnervated muscle fiber-type composition during the 4 weeks after nerve injury.

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  • Cited by (0)

    Supported by the Ministry of Japan Culture, Education and Science (grant no. 14770738).

    1

    No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.

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