We examined the effects of continuous passive motion（ CPM） on membrane type 1-matrix metalloproteinase（ MT1-MMP） expression in rat immobilized muscles. Eight-week-old male Wister rats were used for each of two trials, one with 2 weeks, and another one with 4 weeks of immobilization with/without CPM. In each trial, rats were immobilized（ immobilization group）, and immobilized and simultaneously given CPM （CPM group）. The soleus muscle of each rat was evaluated by gelatin zymography, western blotting and reverse transcription-polymerase chain reaction（ RT-PCR）. Gelatin zymography revealed a greater level of gelatinase activity in the extract of the muscles of the immobilization group than in those of the control and CPM group. The expressions of matrix metalloproteinase 2 （MMP-2） and MT1-MMP mRNA in the muscle extract of the immobilization group were also greater than those in the control and CPM group. Our results suggested that joint immobilization induces expression of MT1-MMP, a cleavage enzyme of MMP-2 in muscles, resulting in muscular degeneration, and that CPM can prevent these changes
