A switched linear dynamical systems framework for modeling individual-specific joint angle trajectories and responses to muscle stimulation during gait

We used switched linear dynamical systems (SLDS) to model joint angle trajectories of healthy individuals walking on a treadmill with and without functional electrical stimulation (FES). We tested the ability of the SLDS models to reproduce the kinematic trajectories based on measured the joint angles at the start of each gait phase. Joint angle trajectories in four gait phases in unperturbed walking were reproduced with a median fitness of 0.80. Individual-specific responses to FES during perturbed walking, were also reproduced with a median fitness of 0.79 by modeling the perturbation as a square wave. SLDS models do not explicitly encode joint angle trajectories but represent inter-joint coupling due to biomechanical and neural constraints. SLDS models may be useful for understanding and simulating individual-specific gait dynamics in health and disease.