摘要Objective: To study the possible mechanism and prevention of disuse muscle atrophy. Methods: The shortened immobilization (plaster fixation) of rat' s soleus muscle (SOL) was used as the model of muscle and the lengthened immobilization of rat' s SOL muscle as "passive stretch" method. Types of skeletal muscle fibers were differentiated with m - ATPase staining technique. The changes of rat' s SOL muscle weight (wet weight) as well as the types and the mean cross - sectional area (CSA) of muscle fibers were examined respectively on day 2, 4,7, 14 and 21 under both shortened and lengthened immobilization and then the effect of passive stretch on soleus muscle atrophy in immobilized rats was observed. Results: When shortened immobilization was applied for 4 days, SOL muscle weight (wet weight) became lighter; the fiber crosssectional area (CSA) shrank and type Ⅰ muscle fibers started transforming into type Ⅱ, which all indicated immobilized muscles began to atrophy and as immobilization proceeded, muscle atrophy proceeded toward higher level. In contrast to that, when lengthened immobilization was applied, SOL muscle didn' t show any sign of atrophy until 7th day, and reached its highest level on day 14 and maintained that level even though immobilization continued. Conclusion: From the results, we conclude that passive stretch can either relieve or defer disuse muscle atrophy.