Investigation of effect of fiber orientation on mechanical behavior of skeletal muscle

Existing studies have included little discussion of anisotropic and material non linearity of muscle tissue, and fiber orientation–based material properties of skeletal muscle tissue are not reported well in literature. There has been some dispute about material response of muscle in different fiber directions. It is necessary to have a better understanding of fiber orientation based material properties of skeletal muscle, to ensure the accuracy of computational models of muscle. To this end, the aim of this study was to investigate fiber orientation–based material properties in vitro and simulate them with finite element analysis (FEA).

Tensile testing was performed on 5 samples of skeletal muscle from a goat at a strain rate of 0.15 s^-1 with fiber orientation along the length (P) and 45° incline to the fiber direction (I). FEA was completed using the experimental condition to validate the results of the in vitro test. The cross-fiber direction was simulated using FEA.

The stresses for all fiber directions at maximum stretch were 1,973.2 kPa for fiber direction P, 1,172 kPa for direction I and 430 kPa for the cross-fiber direction. The tensile strengths of the skeletal muscle were 0.44 MPa for P and 0.234 MPa for I. The elastic modulus of muscle tissue in all fiber directions was 1.59 MPa for fiber direction P (E_p), 0.621 MPa for 45° direction I (E_I) and 0.43 MPa for the cross-fiber direction (E_c). The displacement of the muscle sample against the maximum load was small along the fiber direction. The results of the present study showed that muscle tissue was stiffer in the fiber direction than in the cross-fiber direction.

The stiffness of skeletal muscle is changed as the fiber orientation of skeletal muscle tissue changed.