Comparison of kinematic and EMG parameters between unassisted, fixed- and adaptive-stiffness robotic-assisted ankle movements in post-stroke subjects

Abstract

In this paper, we present an assist-as-needed scheme that effectively adapted the assistance provided by an ankle rehabilitation robot according to patient's participation and performance during therapeutic movements. We performed an error-based estimation of the ankle impedance as a valid measure of the patient participation. Then, we computed the amount of robotic assistance by three steps: normalization of the combined patient-robot stiffness, optimization of patientrobot interaction, and finally, adaptation of the level of the robotic assistance according to patient's performance while playing a serious game. Four post-stroke patients evaluated our methodology using an impedance controlled robotic system to assist alternated open-ended dorsi/plantarflexion movements in sitting position. Experimental results indicated that the proposed adaptive-stiffness method improves patient participation and performance compared to a fixed-stiffness assistive method and to an unassisted baseline. We also found that adaptive assistance could optimize the patient's muscular activity during movements. Our strategy effectively assisted with a lower stiffness allowing more kinematic variability in motions leaded by patient, decreasing the total amount of provided assistance without compromising the overall performance during therapy.