Morphological effects of electrical stimulation and intermittent muscle stretch after immobilization in soleus muscle

The objective of the present study was to assess the effectiveness of a combined protocol of muscle stretching and strengthening after immobilization of the hindlimb. Thirty female Wistar rats were divided into 6 groups: group immobilized for 14 days to cause full plantar flexion by cast (GI, n=6); group immobilized/stretched (GIS, n=6): submitted to the same immobilization and to 10 days of passive stretching; group immobilized/electrically stimulated (GIES, n=6): similarly immobilized and submitted to 10 days of low frequency electrical stimulation (ES); group immobilized/stretched/electrically stimulated (GISES, n=6): similarly immobilized, submitted to 10 days of stretching and ES application; group immobilized/free (GIF, n=3): similarly immobilized and then left with free limbs for 10 days; control group (CG, n=3). The middle portion of the soleus muscle was frozen and sections were stained with HE or mATPase. Morphological analysis revealed high cellular reactivity in the GISES, GIES and GIS groups. The lesser diameter and proportion of type I fibers (TIF) and type II fibers (TIIF) (at pH 9.4) and connective area (at HE stain) were measured with an image analyzer and the data obtained were analyzed statistically by the unpaired Student t-test (p <= 0.05). The results indicated that: a) immobilization generated atrophy of both fiber types (p < 0.05); b) joint application of ES and stretching was not efficient in reestablishing the size of the two fiber types compared to CG (p < 0.05); c) the ES protocol reestablished only the size of TIIF, which showed values similar to those detected in CG (p < 0.05); d) the stretch increased the proliferation of the perimysium connective tissue (p > 0,05). Thus, we conclude that, in the model applied here to female rats, a stretching protocol may limit the volume protein gain of soleus muscle fibers and increase the connective interstitial tissue.