Increased effort during use of the paretic arm and hand can provoke involuntary abnormal synergy patterns and amplify stiffness effects of muscle tone for individuals after stroke, which can add difficulty for user-controlled devices to assist hand movement during functional tasks. We study how volitional effort, exerted in an attempt to open or close the hand, affects resistance to robot-assisted movement at the finger level. We perform experiments with three chronic stroke survivors to measure changes in stiffness when the user is actively exerting effort to activate ipsilateral EMG-controlled robot-assisted hand movements, compared with when the fingers are passively stretched, as well as overall effects from sustained active engagement and use. Our results suggest that active engagement of the upper extremity increases muscle tone in the finger to a much greater degree than through passive-stretch or sustained exertion over time. Potential design implications of this work suggest that developers should anticipate higher levels of finger stiffness when relying on user-driven ipsilateral control methods for assistive or rehabilitative devices for stroke.

翻译：摘要：中风后个体在使用瘫痪手臂和手部时，增加的用力可能诱发非自主的异常协同模式，并放大肌张力对僵硬效应的影响，这增加了用户控制设备在功能性任务中辅助手部运动的难度。我们研究了试图张开或握紧手部时产生的随意用力如何影响手指层面抵抗机器人辅助运动的阻力。我们通过对三名慢性卒中幸存者进行实验，测量了用户主动激活同侧肌电控制机器人辅助手部运动时的僵硬程度变化，并与手指被动拉伸时的情况进行对比，同时评估了持续主动参与和使用的整体效应。结果表明，上肢主动参与导致手指肌张力显著高于被动拉伸或随时间持续用力的程度。本研究的潜在设计启示表明，开发者在依赖用户驱动的同侧控制方法为中风患者提供辅助或康复设备时，应预期更高的手指僵硬水平。