A new model of passive limb motion

Reports on ongoing work in the modeling of the leg drop pendulum test as a means of assessment in spastic cerebral palsy. In previous papers it was demonstrated that a passive model might fit data taken from the passive motion of limbs with and without spastic cerebral palsy outside of the influence of the monosynaptic reflex loop. This paper tests that model further by performing leg drop pendulum tests under anesthesia and muscle paralysis on 11 subjects. The model which best fits the data is different from others reported in the literature. The model consists of 2 nonlinear springs and 2 nonlinear dampers, one for each direction of motion. The nonlinearities consist of simple power functions of position for the springs and velocity for the dampers. Two additional damping elements are added based on the inverse of velocity as the motion comes to rest. The paper demonstrates the accuracy of this model.