Investigation of Effect of Fiber Orientation on Mechanical Behaviorof Skeletal Muscle

Background Existing studies have included little discussion of anisotropic and materialnon linearity of muscle tissue, and fiber orientation–based materialproperties of skeletal muscle tissue are not reported well in literature.There has been some dispute about material response of muscle in differentfiber directions. It is necessary to have a better understanding of fiberorientation based material properties of skeletal muscle, to ensure theaccuracy of computational models of muscle. To this end, the aim of thisstudy was to investigate fiber orientation–based material properties invitro and simulate them with finite element analysis (FEA). Methods Tensile testing was performed on 5 samples of skeletal muscle from a goat ata 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 theexperimental condition to validate the results of the in vitro test. Thecross-fiber direction was simulated using FEA. Results The stresses for all fiber directions at maximum stretch were 1,973.2 kPa forfiber direction P, 1,172 kPa for direction I and 430 kPa for the cross-fiberdirection. The tensile strengths of the skeletal muscle were 0.44 MPa for Pand 0.234 MPa for I. The elastic modulus of muscle tissue in all fiberdirections was 1.59 MPa for fiber direction P (Ep), 0.621 MPa for45° direction I (EI) and 0.43 MPa for the cross-fiber direction(Ec). The displacement of the muscle sample against themaximum load was small along the fiber direction. The results of the presentstudy showed that muscle tissue was stiffer in the fiber direction than inthe cross-fiber direction. Conclusions The stiffness of skeletal muscle is changed as the fiber orientation ofskeletal muscle tissue changed.