SKELETAL MUSCLE IN COMPRESSION: MODELING APPROACHES FOR THE PASSIVE MUSCLE BULK

Abstract

The internal loading distribution within the body cannot generally be measured. In contrast, musculoskeletal models have the potential to predict internal stress-strain patterns at all locations within the body. However, this often requires an adequate model of the constitutive behavior of skeletal muscle tissue. Thus far, all attempts at formulating the stress response of skeletal muscle have assumed that the total stress has active and passive components that can be added to yield the total response. In quasi-static applications such as pressure-sore modeling, and in dynamic applications involving transient external loading (especially impact modeling), the passive muscle representation may be more relevant than the active response. This paper summarizes the known passive deformation behavior of skeletal muscle tissue and reviews the constitutive formulations for passive muscle that are included in combined active/passive muscle models. It is shown that none of the existing formulations can adequately represent the asymmetry in the tension/compression stress-strain response, the anisotropy in compression, and the viscoelastic phenomena that have been experimentally observed. To address these shortcomings, a number of modeling developments are proposed. In particular, it is suggested that explicit recognition of the rate dependency of the stress response of skeletal muscle in compression may provide significant benefits. Furthermore, explicit recognition of the high fluid content in skeletal muscle through the development of a poroelastic formulation may be more beneficial than further advances in micromechanical modeling based purely on a solid formulation.