Effect of Skeletal Muscle Immobilization on Regional Anisotropic Viscohyperelastic Properties Change in a Rat Model

Objectives

The passive mechanical properties of immobilized skeletal muscle in short position were investigated over time. The purpose of this study was to explore in three different zones (distal, proximal and medial) of the biceps brachii immobilized of rats in short position and its free contralateral.

Material and methods

In vitro equibiaxial relaxation tests were performed from samples harvested from immobilized skeletal muscles of rats during one or two weeks. Material parameters were identified by using a viscohyperelastic model described by an anisotropic strain energy function coupled with second order Maxwell's model.

Results

The excising zone of samples greatly influenced the parameters of the hyperelastic behavior while the immobilization had effects on the viscoelasticity response instead. Based on measurements of histological parameters from flexor carpi ulnaris muscles, the immobilization produced contractile tissue atrophy and connective tissue thickening. A correlation between mechanical and structural characteristics was given. The histological analysis permitted to quantify fibrosis in the immobilized skeletal muscle and to correlate with the mechanical behavior change.

Conclusion

The immobilization of skeletal muscles in short position is highly deleterious. Immobilized rats displayed marked atrophy of skeletal muscle, fibrosis of the extracellular matrix and a tendency to visco-hyperelastic parameter changes. This work has the potential to be useful for future research on neuromuscular diseases like spastic myopathy which leads to muscular immobilization.