Mechanical and microstructural changes of skeletal muscle following immobilization and/or stroke.

Patient management following a stroke currently represents a medical challenge. The presented study investigates the effect of immobilization on skeletal muscles in short positions after a stroke. A rat model was implemented in order to compare four situations within 14 days including control group, immobilization of one forelimb without stroke, stroke without immobilization and stroke with immobilization of the paretic forelimb. To analyze the changes of the mechanical properties of the passive skeletal muscle, the biological tissue is assumed to behave as a visco-hyperelastic and incompressible material characterized by the first-order Ogden's strain energy function coupled with second-order Maxwell's model. The material parameters were identified from inverse finite element method by using uniaxial relaxation tests data of skeletal muscle samples. Based on measurements of histological parameters, we observe that muscle immobilization led to microconstituents changes of skeletal muscles that were correlated with degradations of its mechanical properties. In the case of immobilization without stroke, the neurological behavior was also altered in the same manner as in the case of a stroke. We showed that immobilization of skeletal muscles in short positions produced contractile tissue atrophy, connective tissue thickening and alteration of passive mechanical behavior that were more damaging than the effects produced by a stroke. These results showed then that immobilization of skeletal muscles in short positions is highly deleterious with or without a stroke.