In order to investigate how spasticity disrupts the capabilities of the human body, a better understanding of how joint impedance control operates in healthy individuals is necessary. In this investigation, a second order rotary torque model was implemented to investigate the impedances at the metacarpophalangeal (MCP) joint of the index finger. The model was fit to approximately 25 milliseconds of force and displacement data to determine the mechanical impedances at the finger tip. Ranges of damping and stiffness were optimized over a range of mean finger tip force (0-12 N) for extension. The equilibrium-point hypothesis was examined when compared to the theory that joint stiffness changes linearly with applied initial force, presented by researchers including Hajian and Howe.

Results confirm Feldman's findings that stiffness and damping are relatively constant across levels of increasing applied force. Equilibrium angle R as presented by Feldman and represented by theta-not in this analysis was shown to be the driving control mechanism in active force regulation. The equilibrium angle increased nearly linearly as force increased. This also contradicts the notion that joint stiffness increases linearly with applied initial force. Protocols for conducting experiments on individuals with spasticity were developed. Future work will implement these protocols to conduct an investigation of the joint impedance of spastic individuals.