Correlating Skeletal Muscle Output Force and Intramuscular Pressure via a 3-Dimensional Finite Element Muscle Model.

PURPOSE The inclusion of muscle pressure in muscle models may have important implications in biomechanics. This notion builds from the known correlation between muscle contractile force and internal pressure. However, this relation is often omitted in numerical models leveraged to study biomechanics. Thus, the purpose of this study was to develop and validate a method of modeling muscles, via finite elements, inclusive of the correlation between muscle contractile force and intramuscular pressure. METHODS A MRI-scanned tibialis anterior muscle was modelled via a simple, yet easily scalable, mixed shell and pressure finite element model. Then a validation study was conducted on intramuscular pressure, resulting from applied muscle contractile force, through leveraging special fluid elements type. RESULTS The fluid-structure based model and adopted methods exhibited muscle forces and intramuscular pressure that were highly linearly correlated. Indirect validation was achieved with a maximum discrepancy of 7.25%. Furthermore, force-length curves followed a trend similar to documented conventional muscle data during concentric contraction, which added to the model's validity. Mesh, material properties, and tendon stiffness sensitivity studies supported model's robustness. CONCLUSION This study has introduced a novel 3-dimensional finite element modelling method that respects the physiological force and intramuscular pressure relationship. Although similar models have been previously explored, their complex physiological representation and time-consuming solvers make their scalability and real-time implementation questionable. Thus, the developed model may address such limitations while improving the realism of volumetric finite element models inclusive of muscle contribution.