Fast quantification of arm impedance during multijoint reaching following stroke - Rehabilitation Institute of Chicago

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Fri, Sept 24

Speaker: Davide Piovesan, PhD

Title: Fast quantification of arm impedance during multijoint reaching following stroke. 

Abstract:  Arm muscle activity coordination is often severely impaired following stroke. When generating point-to point reaching movements, abnormal activation patterns emerge, characterized by an excessive muscle coupling that can significantly limit the use of the paretic limb, and impair daily living activities.

Following stroke, the majority of studies quantifying limb mechanics and spinal contributions to those mechanics have focused on passive, single joint movements. The main result of those studies shows an alteration in the reflex modulation and an increase of joint stiffness post-stroke, suggesting an implication of stiffness modulation in the abnormal motor path.

In this study we investigated the modulation of endpoint stiffness during point-to–point multijoint reaching movement in stroke survivors. We introduced a new technique based on a time-frequency domain analysis, which can estimate a time-varying profile of arm impedance without the need of numerous movement repetitions. Our objective was to quantify the impedance variation during reaching movement thereby observing the impact of such modulation with muscle discoordination.

We found that the estimated impedance increases accordingly with the level of spasticity described using the modified Ashworth scale. Impedance varies along the course of the movement between stable and unstable configurations. Substituting the measured stiffness profile in a simple mechanical simulation we were able to reproduce similar synergistic patterns to those observed following stroke.