Simulating the pendulum test to understand mechanisms of parkinsonian rigidity

The pendulum test has been used to objectively quantify spasticity, but its utility in Parkinsonian rigidity has been studied much less. Our recent simulations suggest that key features of abnormal pendulum test kinematics can be attributed to elevated muscle tone and reflex gain in spastic cerebral palsy. We hypothesized that muscle tone is also increased in Parkinsonian rigidity. We tested individuals with varying degrees of rigidity using the pendulum test, and simulated the resulting kinematics. Our experimental and simulation results suggest a major role of elevated muscle tone in Parkinsonian rigidity. Our work suggests that the pendulum test could be an effective tool for evaluating the mechanisms of rigidity in Parkinson’s disease (PD).