Biomechanical models for modified pendulum test of the upper limb

The main goal of this study was to develop and evaluate biomechanical models for interpreting the results of pendulum test of the elbow. Three biomechanical models with different degrees of complexity were proposed. Model 1 consisted of simple spring and damping elements. In model 2, non-linear damping element was added. In model 3, a structure of thixotropic effect was added. By using optimization techniques, we estimated parameters from these models as the candidate indicators of spasticity. In model 1, the estimated stiffness constant and damping coefficient were larger in stroke patients with spasticity. In model 2, though adding a non-linear damping term marginally improved the optimization, the added non-linear damping effect was not more prominent in the stroke patients. In model 3, no unique solution could be obtained. We concluded that, for analyzing the results of upper limb pendulum test, increasing the complexity of models did not increase the capability to differentiate spasticity from normotonus. From the simple linear model, both stiffness constant and damping coefficient were increased in the stroke patients with spasticity.