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Without finger function, people with C5-7 spinal cord injury (SCI) regularly utilize wrist extension to passively close the fingers and thumb together for grasping. Wearable assistive grasping devices often focus on this familiar wrist-driven technique to provide additional support and amplify grasp force. Despite recent research advances in modernizing these tools, people with SCI often abandon such wearable assistive devices in the long term. We suspect that the wrist constraints imposed by such devices generate undesirable reach and grasp kinematics. Here we show that using continuous robotic motor assistance to give users more adaptability in their wrist posture prior to wrist-driven grasping reduces task difficulty and perceived exertion. Our results demonstrate that more free wrist mobility allows users to select comfortable and natural postures depending on task needs, which improves the versatility of the assistive grasping device for easier use across different hand poses in the arm’s workspace. This behavior holds the potential to improve ease of use and desirability of future device designs through new modes of combining both body-power and robotic automation. 

Loss of hand function severely impacts the independence of people with spinal cord injuries (SCI) between C5 and C7. To achieve limited grasps or strengthen grip around small objects, these individuals commonly employ a compensatory technique to passively induce finger flexion by extending their wrist. Passive body-powered devices using wrist-driven actuation have been developed to assist this function, in addition to advancements in active robotic devices aimed at finger articulation for dexterous manipulation. Nevertheless, neither passive nor active devices see wide adoption and retention in the long-term. Here we present an unconventional system for combining aspects of both passive and active actuation and show that actively modulating the relationship between passive wrist and finger movement can impact both performance and kinematic metrics of upper body compensation. This study comprises six unique case studies of individuals with C5-6 SCI because morphology and response can vary widely across this population. While only some individuals’ performance improved with the shared system over passive-only operation, all six participants stated that they preferred the shared system, regarding added motorization with a sense of trust and embodiment. This outcome motivates the ongoing study of how motors can alter body kinematics to augment body-power without replacing it.