SPECIFICALLY TAILORED USE OF THE FINITE ELEMENT METHOD TO STUDY MUSCULAR MECHANICS WITHIN THE CONTEXT OF FASCIAL INTEGRITY: THE LINKED FIBER-MATRIX MESH MODEL

In addition to providing a great advantage that geometrically highly complex structures can be modeled, the finite element method also allows addressing complex mechanics concepts such as nonlinear material properties and large deformations. These capabilities are highly valuable for studying skeletal muscle mechanics and were successfully implemented by several researchers. Certainly, those models made an important contribution to our understanding of fundamental muscle physiology. A common modeling consideration was that the myotendinous force transmission was regarded as the exclusive mechanism of exertion of muscle force. However, if muscular structures are considered to operate within the context of fascial integrity (the condition in vivo), additional mechanical connections, hence force transmission pathways to the myotendinous ones must be taken into account, i.e., (i) muscle fibers and intramuscular connective tissue stroma are connected to each other not only at the ends but also along the full length of the muscle fibers and (ii) in vivo muscle is not an isolated entity, i.e., direct collagenous linkages exist between epimysia of adjacent muscles and fascial structures (e.g., neurovascular tracts, compartmental boundaries) and provide connections between muscular and nonmuscular structures at several locations additional to the muscle's tendinous insertion and origin. These nonmyotendious connections have been shown to transmit substantial amounts of muscle force, i.e., intra- and epimuscular myofascial force transmission. The linked fiber-matrix mesh (LFMM) model was designed specifically to study muscular mechanics within the context of fascial integrity, i.e., (i) two separate but elastically linked meshes representing muscle fiber and extracellular matrix domains were used to model muscle tissue and (ii) muscles' epimuscular connections were accounted for. Therefore, it was aimed at addressing the effects of intra- and epimuscularly myofascial force transmission on muscular mechanics, e.g., changes in sarcomere lengths. The goal of this article is to provide a comprehensive description of the LFMM model and to review its contribution to muscular mechanics.