Clarification of micro damage mechanism of skeletal muscle tissue and formulation of a constitutive model of muscle taking into account the damage

从损伤预防的角度出发，阐明和预测微损伤的判据，以及微损伤的演化导致生物功能和强度降低的机制是非常重要的。本研究的目的是构建一个考虑骨骼肌微损伤的力学模型框架。首先，我们评估了肌肉组织的微损伤与其力学功能在应变损伤和肌肉挫伤中的变化之间的关系，以阐明微损伤对骨骼肌力学性能的影响。为了检验考虑生物组织微损伤演化的力学模型框架，我们构建了一个具有相对简单力学特性的皮质骨本构模型。该模型考虑了弹性模量的应变率依赖性、变形和强度的各向异性、拉伸、压缩和剪切变形和强度的不对称性，以及微损伤的累积引起的断裂。建立了骨骼肌的力学模型，并将仿真结果与相应的肌肉拉伸和损伤实验结果进行了比较。我们将损伤力学的框架应用于Holzapfel等人提出的生物组织粘弹性模型。在这个模型中，我们假设骨骼肌是一种横向各向同性的粘弹性材料，微损伤也是横向各向同性的。结果表明，该模型较好地描述了应变损伤的特征。

From the viewpoint of injury prevention, it is very important to clarify and predict the criteria of micro damage and the mechanism of the decrease of the biological function and strength by the evolution of the micro damage. The motivations of this study are to construct a framework of a mechanical model which takes into account the micro damage of skeletal muscle.Firstly, we evaluated the relationship between the micro damage of muscular tissue and the change of its mechanical functions on strain injury and muscle contusion to clarify the influence of the micro damage on the mechanical properties of skeletal muscle. We also discussed the dependences of the activity of muscle and strain rate of the mechanical properties of muscle fascicle.To examine a framework of a mechanical model considering micro damage evolution of biological tissue, we constructed a constitutive model of cortical bone, which has relatively simple mechanical propeties. The developed model takes account of the strain rate dependency of the elastic modulus, anisotropies of the deformation and strengths, asymmetries of the deformation and strengths for tension, compression and shear, and the fracture caused by the accumulation of the micro damage.A mechanical model considering the difference of fatigability of motor unit was also studied. The proposed model represented a macroscopic fatigability of skeletal muscle qualitatively.We formulated a mechanical model of skeletal muscle and compared the simulation results with the corresponding experimental results of tensile and injury experiments of muscle. We adopted the framework of damage mechanics into the viscoelastic model for biological tissue proposed by Holzapfel et al. In this model, we assumed that skeletal muscle is a transverse isotropic viscoelastic material, and the micro damage also evolves tranverse isotropically. It was confirmed that the proposed model described the characteristic features of strain injury well.