The Neural Contribution to Passive Joint Movement in Individuals with Cerebral Palsy

The original objective of this study was to quantify spasticity in a spastic subject using the Pendulum Knee Drop test. An interesting phenomenon was observed while analyzing the collected data. The neural contribution in defining or changing the set point for a passive joint movement is not well understood, therefore, the purpose of this paper is to explain the noted phenomenon according to the Equilibrium Point Hypothesis with which we can justify the changes in moments during PKD test. In passive limb movements the virtual trajectory follows the actual trajectory; in contrast for an active movement the desired trajectory precedes the actual trajectory. The present data explains passive knee movement during PKD for a CP individual and describe the changes in joint moment as function of θ_vt assigned by the CNS.