Abstract
We determined the effect of stretching applied once a week to the soleus muscle immobilized in the shortened position on muscle fiber morphology. Twenty-six male Wistar rats weighing 269 +/- 26 g were divided into three groups. Group I, the left soleus was immobilized in the shortened position for 3 weeks; group II, the soleus was immobilized in the shortened position and stretched once a week for 3 weeks; group III, the soleus was submitted only to stretching once a week for 3 weeks. The medial part of the soleus muscle was frozen for histology and muscle fiber area evaluation and the lateral part was used for the determination of number and length of serial sarcomeres. Soleus muscle submitted only to immobilization showed a reduction in weight (44 +/- 6%, P = 0.002), in serial sarcomere number (23 +/- 15%) and in cross-sectional area of the fibers (37 +/- 31%, P < 0.001) compared to the contralateral muscles. The muscle that was immobilized and stretched showed less muscle fiber atrophy than the muscles only immobilized (P < 0.05). Surprisingly, in the muscles submitted only to stretching, fiber area was decreased compared to the contralateral muscle (2548 +/- 659 vs 2961 +/- 806 microm(2), respectively, P < 0.05). In conclusion, stretching applied once a week for 40 min to the soleus muscle immobilized in the shortened position was not sufficient to prevent the reduction of muscle weight and of serial sarcomere number, but provided significant protection against muscle fiber atrophy. In contrast, stretching normal muscles once a week caused a reduction in muscle fiber area.
Highlights
An important question for rehabilitation is how to protect skeletal muscle from the effects of immobilization, especially muscles immobilized in the shortened position
A previous report showed that daily sessions of passive stretching applied for 30 min to the soleus muscle of rats immobilized in the shortened position were enough to prevent the loss of serial sarcomeres and to maintain the joint range of motion [2]
The present study showed that passive stretching applied once a week for 40 min over a period of 3 weeks to the soleus of rats immobilized in the shortened position was not enough to prevent the loss of serial sarcomeres, but promoted significant protection against the muscle fiber atrophy
Summary
An important question for rehabilitation is how to protect skeletal muscle from the effects of immobilization, especially muscles immobilized in the shortened position. It is well known that skeletal muscle is an adaptable tissue which, when immobilized in the shortened position for 3 weeks, presents loss in the number of serial sarcomeres, muscle fiber atrophy and proliferation of connective tissue [1,2,3]. These changes contribute to the significant reduction of the joint range of motion when the immobilization is removed. Muscle stretching is recognized as a very powerful stimulant of muscle growth and protein synthesis (for reviews, see Refs. 8,9)
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