Simulation of biceps femoris muscle growth based on stretch unisg a multiscale model for sarcomere addition

An applicable tool for professionals, who are involved in curing musculoskeletal disorders, including physical medicine and rehabilitation specialists and orthopedic surgeons, is recognition the process of muscle tissue growth and determining the areas which are vulnerable to different types of injuries or rupture. In this study, by considering hyper-elastic behavior for materials of the muscle, the finite growth relations have been applied using the decomposition of deformation gradient tensor to two parts of the elastic and growth. Consequently, the continuum relations were combined with the growth evolution equation and a series of mechanobiological relations were obtained. To solve them, a user material subroutine UMAT code was written in FORTRAN based on finite element software ABAQUS. Then the biceps femoris – long head muscle was modeled as a cylinder and the simulation was based on a 6-week period and a 10% increase in initial length. As a result of the simulation, it was found that maximum stretches occur in the surfaces, and not inside the muscle and they reach 1.04 in near the proximal muscle-tendon junction in the posterior layer and 1.06 in distal muscle- muscle-tendon junction in the posterior layer and 1.06 in distal muscle-junction in interior layer. Also, by examining how the growth dispersed, it was found that the muscle grows heterogeneously. This numerical simulation provides valuable results, such as; correct and optimal diagnosis of treatment, helping patient’s rehabilitation, and orthopedic surgeries.