Mechanical behavior of skeletal muscles under simple shear at large strain

The study of the shear response of skeletal muscles has a great importance for understanding, preventing, and diagnosing diseases. The purpose of this work is to investigate the highly nonlinear mechanical behavior of skeletal muscle under simple shear at large deformation. The influence of preload, strain rate and fiber orientation on the bovine tissue response was experimentally examined. Two apparatuses were developed to cut and test all samples. The amount of shear was obtained using digital image correlation method. As expected, the preload and strain rate can influence the shear response of muscle. The effect of fiber orientation was investigated considering a quasistatic condition and no preload. There was no apparent difference between the initial stiffnesses when skeletal muscle was sheared in the three principal modes. The initial stiffness of skeletal muscle increased when fiber bundles were oriented at 45º with respect to shear load direction. At large deformation, the shear response can be affected by the structural failure of tissues. However, results indicated that longitudinal shear is less susceptible to failure. A phenomenological model based on three physical parameters was proposed to describe the nonlinear mechanical behavior of the skeletal muscle tissue under simple shear. A good agreement between experimental data and model was observed.