Micromechanical Study On The Mechanical Characteristic Of The Skeletal Muscle Epimysium

The muscle is the main component of biological movement system and only motivity of active movement. Skeletal muscle is a source of Human strength, but also of human movement "engine", skeletal muscle is one of the most important tissues, it is widely distributed in animals, accounting for about 40% body weight. Microstructure and mechanical properties of skeletal muscle determine the human achievement of active exercise. Therefore, the many disciplines of human exercise science study the muscle as important topic. In this paper, according to microstructure of skeletal muscle epimysium, in the regime of nonlinear elasticity theory, the variational principle was adopted to develop two micromechanical models to study the deformation behavior of skeletal muscle epimysium under load. In these models we assume that the collagen fiber is fixed at both ends, and used the constraints of incompressible biological soft tissue and rule of mixtures of biocomposite materials.Firstly, an equidirectional model with definite physical picture, fewer parameters and simple structure was established in the framework of micromechanics, by which the microstrucutre and the stress-stretch ratio relationship of the skeletal muscle epimysium was modeled and analyzed. Furthermore, considering quasi-periodic geometry of the collagen fibers in the skeletal muscle epimysium, the case in which the unit cell contains a collagen fiber with period greater than one. And the role of the multiperiod geometry on the stress-stretch ratio relationship of the skeletal muscle epimysium. The age related macromechanical characteristic of the epimysium was discussed by calculating the stress-stretch ratio relationship for skeletal muscle epimysium from old and young rats with partially experimental and fitted parameters. The results agree with the experimental results in the error range.Secondly, on the basis of the second chapter, a more general micromechanical model of uniform and collagen fibers in different directions was established. In this model the Boltzmann statistics are adopted to calculate the direction distribution probability of the repeated unit cell contains the collagen fiber. In addition, the stress-stretch ratio relationship is effectively obtained from such relationship of unit cells.As the discussions presented in the former chapter, the micro structure of the skeletal muscle epimysium from old and young rats was modeled and the stress-stretch ratio of bio-soft tissue was calculated and analyzed. Furthermore, the macro-mechanical properties of the skeletal muscle epimysium were discussed by combing such factors as aging process, measurement temperature. And some numerical results are compared with the recent theoretical and experimental results. It is shows that the model presented in this chapter is closer to the experimental results. This fact demonstrates that the model is efficient and viability.Finally, it is shown that the modeling method presented in this paper is not only applicable to the epimysium, but also useable to other bio-soft tissues such as endomysium. Even though our discussion is partially based on the Ref. [40], our model is more general and the numerical results are more close to the experimental results when compared to the ref. [40]. It may be worthy to the comprehension of the origin of bio-soft tissues' macro-mechanical characteristic.