A Model of Chronically Stretched Soleus Muscle in Rat

To obtain an experimental model which could be used to investigate the effect of chronic muscle stretching on neuromuscular transmission, a series of experimental observations were carried out using rats. The following results were obtained. 1. Not only the soleus muscle but also the gastrocnemius muscle was stretched in the leg-lengthening (LL)-operated leg. In contrast, in the leg subjected to the leg-lengthening operation with dislocation of the knee joint (LLD operation), the gastrocnemius muscle was not stretched, although the soleus muscle was stretched as much as in the LL-operated leg. 2. The degree of dorsiflexion of the foot and the extent of the restriction of the ankle joint's movement were severe in the LL-operated leg. They were slight in the LLD-operated leg. 3. The wet weight of the soleus muscle in the LL-operated leg decreased gradually as the stretching period increased. The wet weight in the leg subjected to a fixation procedure performed by a plaster cast, so as to obtain an immobilization model, was similar to that in the LL-operated leg. However, no significant difference in wet weight in the LLD-operated leg was observed during the stretching period, compared with the control. On the basis of these results, it was concluded that the LLD operation was more suitable than the LL operation as a method to obtain a model which could be used to investigate the effect of chronic muscle stretching on neuromuscular transmission