Immobilization effect on the tensile properties of striated muscle: an experimental study in the rat.

To investigate the effect of immobilization on the tensile properties of atrophied gastrocnemius muscle, the left hind legs of 40 rats were fixed with padded plaster casts for three weeks. Seven to 42 days after starting the immobilization, load-deformation curves were registered from both gastrocnemius muscles of each rat and several parameters assessed from the curves. The rupture always occurred at the muscle belly. The decrease in breaking strength and energy absorption capacity following immobilization for one week averaged 20% and 34%, respectively, and the values fell further to about 32% and 46% at the end of the immobilization (21 days), when compared to the contralateral control muscles of the same animals. The elastic stiffness of the immobilized muscles was markedly decreased but rose nearly to the level of the controls after removal of the casts. The tensile properties of the previously immobilized muscles had not yet reached the control levels three weeks after removal of the casts.