Arm Stiffness During Assisted Movement After Stroke: The Influence of Visual Feedback and Training

Abstract

Abstract-Spasticity and muscular hypertonus are frequently found in stroke survivors and may have a significant effect on functional impairment. These abnormal neuro-muscular properties, which are quantifiable by the net impedance of the hand, have a direct consequence on arm mechanics and are likely to produce anomalous motor paths. Literature studies quantifying limb impedance in stroke survivors have focused on multijoint static tasks and single joint movements. Despite this research, little is known about the role of sensory motor integration in post-stroke impedance modulation. The present study elucidates this role by integrating an evaluation of arm impedance into a robotically mediated therapy protocol. Our analysis had three specific objectives: 1) obtaining a reliable measure for the mechanical proprieties of the upper limb during robotic therapy; 2) investigating the effects of robot-assisted training and visual feedback on arm stiffness and viscosity; 3) determining if the stiffness measure and its relationship with either training or visual feedback depend on arm position, speed, and level of assistance. This work demonstrates that the performance improvements produced by minimally assistive robot training are associated with decreased viscosity and stiffness in stroke survivors' paretic arm and that these mechanical impedance components are partially modulated by visual feedback.

Inter-Joint Coordination Deficits Revealed in the Decomposition of Endpoint Jerk During Goal-Directed Arm Movement After Stroke

“…Anomalous reflexes can also alter the apparent endpoint stiffness of the limb. 64,65 This could cause deficits in multi-joint coordination if, as suggested by, 66 the CNS normally solves the problem of controlling the limbs using a passive motion paradigm wherein the elastic energy at the joints is regulated via modulation of joint stiffness ( , ) (see also 8). In this case, joint stiffness is a function of both the limb's position in joint space and the activations of mono-and bi-articular muscles, all of which are functions of time.…”

“…Therefore, it is possible that the variations in jerk components we observed experimentally might also be explained in part by an abnormal modulation of joint stiffness, which is often observed in stroke survivors. 65 Future studies should investigate the role of volitional control of joint stiffness in the modulation of endpoint jerk, how such control may be compromised throughout the workspace post-stroke by spasticity and other deficits of neuromuscular control, and the extent to which impaired control of joint stiffness can degrade the ability to compensate for inter-joint interaction torques that normally arise during multijoint movements.…”

Haptic perception of multi-joint hypertonia during simulated patient-therapist physical tele-interaction

“…Based on such data, we assumed the average joint passive stiffness of unimpaired individuals as the lower boundary of joint rigidity, namely: $K_q=\left(\begin{array}{cc}2& 0.5\\ 0.5& 1\end{array}\right)false[N·m/\mathrm{italicrad}false]$. The upper boundary of joint rigidity was set as $K_q=\left(\begin{array}{cc}14& 3\\ 3& 8\end{array}\right)false[N·m/\mathrm{italicrad}false]$, this value corresponds to the passive stiffness recorded on stroke survivors with Modified Ashworth Score (MAS) equal to 4 [14, 15]. …”

Progress and prospects of the human–robot collaboration

“…In bimanual visuomotor tasks, even perturbed by deviating force fields, humans rapidly learn to control the interaction-forces by a combination of arm stiffness properties and direct force control [Squeri et al, 2010]. This property of the human mo-tor control system is exploited in robot assisted rehabilitation, where often assistance is provided by robotic devices via haptic signals [Morasso et al, 2007], to the point of changing the arm impedance and viscosity in impaired subjects [Piovesan et al, 2013].…”