Biomechanical model of human leg motion

Each year, around 6 million Americans visit either orthopedic surgeons or emergency rooms due to knee problems, and rehabilitation of the knee joint costs $470 million annually in the US. Such extremely high cost demands an auxiliary device, a rehabilitation robot, to facilitate the recuperation of the knee and requires a good description of limb motion. To reduce the cost of recuperation by limiting physical therapy sessions, an intelligent brace enabling accurate positioning of the impaired limb while simultaneously providing assistance or resistance forces to assist the patient's movements is needed. Development of the rehabilitation robot requires a good description of limb motion. Extensive research has been carried out to investigate the biomechanical properties of muscles, ligaments, and bones in static situation. Previous studies have also characterized effects of leg swing on the stability of running motion and the motion profiles of the human leg during walking or jumping. However, the dynamic motion profiles have not linked the model parameters to measured biomechanical properties of muscles, ligaments, and knee damping. Accordingly, in this study we have developed a mathematical model of human leg motion using Lagrangian mechanics to describe dynamic motion profiles of the human leg. The mathematical model used mechanical components such as springs, links, and dashpots to approximate the biological components within the leg. The model parameters are chosen based on published biological experiments. The mathematical model was simulated with MATLAB and validated via comparison of the model predictions against real human leg motion profiles. Our mathematical model can predict the motion profiles of human leg motion and provides a foundation for the development of a rehabilitation robot to assist patient recovery from knee surgery and replacement.