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：中风后个体在使用偏瘫手臂和手部时增加用力会引发不自主的异常协同模式，并放大肌张力导致的僵硬效应，这可能增加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施加的意志努力如何影响手指层面抵抗机器人辅助运动的情况。我们对三名慢性中风幸存者进行实验，测量当用户积极施加努力以激活同侧肌电控制的机器人辅助手部运动时，相比手指被动拉伸时的僵硬变化，以及持续主动参与和使用产生的整体效应。我们的结果表明，上肢主动参与使手指肌张力增加的程度远超过被动拉伸或长期持续用力所导致的效果。本工作的潜在设计启示表明，在为中风患者开发辅助或康复设备时，若依赖用户驱动的同侧控制方法，设计者应预期到更高程度的手指僵硬。