Co-activation and eEMG-feedback for Restoring Hand-Functions

This contribution considers a neuroprosthesis for people who have (partially) paralyzed hand functions as a typical result of a stroke or spinal cord injury. Functional Electrical Stimulation (FES) is applied to three forearm-muscles to induce artificial muscle contractions causing wrist extension/flexion and grasping, respectively. The aim is to control and stabilize the wrist joint angle. Herein, a co-activation to increase the stiffness of the wrist joint is applied to yield a better tolerance to external influences. Doing so, a better motor precision is expected compared to other approaches. To maintain the level of co-activation also under the progression of muscle fatigue, the muscle activation is estimated and controlled using an underlying feedback of the electrical muscle responses as caused by motor unit recruitment. The control system was preliminary tested on two healthy subjects, and a wrist positioning error of 4.5° on average was obtained demonstrating the feasibility of the co-activation based approach.
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1This work was supported by a postdoc fellowship of the German Academic Exchange Service (DAAD). We acknowledge Axelgaard Manufacturing Ltd for donating the stimulation electrodes. Further, we like to acknowledge Astrid Bergman for preparing the used inertial sensor set up.