Effects of 40 min of maintained stretch on the soleus and plantaris muscles of rats applied for different periods of time after hindlimb immobilization

Stretching is frequently used in physiotherapy to minimize or even reverse the alterations that occur after muscle disuse. Alterations that occur after 10 and 21 days of maintained stretch in soleus and plantaris muscles post-disuse were evaluated in the present study in experimental rats. Thirty adult female Wistar rats were divided into seven groups: hindlimb immobilization for 10 days; immobilization and 10 days stretched; immobilized and 21 days stretched; three control groups consisting of animals of different ages and anesthetized group. The right hindlimb was immobilized using a lightweight apparatus composed of two sections: (i) upper part: a small cotton T-shirt and, and (ii) lower part: a steel mesh to fix the ankle in plantar-flexion-shortened position. Fragments of the soleus and plantaris muscle were frozen and processed using histochemical and immunohistochemical methods. Limb immobilization caused important morphological alterations in skeletal muscle including: reduction in the number of type I fibers and an increase in type IIC fibers, reduction in the lesser diameter of type I, IIA and IIAD fibers and in the number of capillaries in soleus muscle. The stretching program applied for 10 days was insufficient to allow recovery from the disuse alterations in both muscles. However, after 21 days there were improved morphological characteristics, size and distribution of the different fibers.