title: The effect of limb immobilization on muscle function and protein composition.
abstract: The treatment of skeletal injuries often requires immobilization for extended periods. Immobilization causes muscle disuse atrophy, which extends the duration of incapacitation following the healing of the skeletal injury. To evaluate the role of immobilization position on the skeletal muscle, an experimental study using an animal model was undertaken. Cats were divided into four groups, with one hind limb immobilized in a plaster spica cast such that the gastrocnemius and soleus muscles were held in either a stretched, shortened, or neutral position. After four weeks of immobilization, functional and quantitative assays of muscle tissue were obtained and correlated. The shortened muscles weighed less, had a lower total content and concentration of myofibrillar proteins (the contractile protein of muscle tissue), and generated less maximum tetanic tension than either the muscles held in neutral or stretched length position. Decreased maximum tetanic tension resulted from the preferential loss of contractile protein. The remaining myofibrillar protein in the shortened muscle showed contractile dysfunction. The ability to maintain initial twitch strength (an endurance function) for five minutes varied with position but was not statistically significant in this study. The data suggest that muscle maintained in a shortened position atrophies more rapidly, with greater loss in contractile function and myofibrillar and sarcoplasmic proteins than the stretched and neutrally positioned muscles.
mesh_terms: D000818:Animals; D002370:Casts, Surgical / Q000009:adverse effects*; D002415:Cats; D003285:Contractile Proteins / Q000032:analysis; D008297:Male; D009119:Muscle Contraction; D009129:Muscle Tonus; D009132:Muscles / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000209:etiology / Q000503:physiopathology*; D009210:Myofibrils / Q000032:analysis; D009929:Organ Size; D011187:Posture
chemical_list: D003285:Contractile Proteins