Systems and methods for numerically simulating muscle's movements along bones and around joints are disclosed. A computerized model containing a plurality of truss elements along with one or more rollers is used. The truss elements are configured for modeling a muscle strand while each roller is configured for a joint. Each truss element includes two end nodes and is configured or associated with a muscle bio-mechanical property model. Each roller is fixed at the location of a corresponding joint. To simulate the muscle strand movements around the joint, each pair of truss elements straddling a roller is adjusted dynamically in a time-marching simulation (e.g., computer simulation of an impact event of an automobile and one or more occupants). Adjustments are performed at each solution cycle of the time-marching simulation. Adjustments include two types—“slipping” and “swapping”.