One-minute bouts of passive stretching after immobilization increase sarcomerogenesis in rat soleus muscle

ABSTRACT

Although the effect of stretching on skeletal muscle has been investigated, the mechanical influence of short bouts of passive stretch, commonly used in rehabilitation therapy to recover skeletal muscle length after immobilization, has not been studied in detail. The hypothesis of this study was that one-minute bouts of muscle stretching applied after immobilization would induce sarcomerogenesis in muscle fibers. To assess this hypothesis, sessions of passive stretching (10 stretches of 1 min each with 30 s rests between stretches) were applied daily or three times a week to the left soleus muscle after immobilization in the shortened position. Eighteen rats were immobilized for four weeks and divided into three groups 1) after immobilization, the rats remained free for three weeks, 2) the soleus muscle was stretched daily for three weeks, and 3) the soleus muscle was stretched three times a week for three weeks. A control group was run in parallel. The crosssectional area of the soleus muscle fibers and the serial number and length of sarcomeres were measured. Both of the stretch protocols increased the serial number of sarcomeres, but not the cross-sectional area of the muscle fibers. In conclusion, short bouts of passive stretching alter the muscle fiber tropism and induce serial sarcomerogenesis after immobilization.