Stroke Leads to Abnormal Coordination of the Multiple Upper Extremity Joints During Passive Movement

Background Motor impairments in the upper extremity (UE) is one of the most common deficits after stroke. Even though understanding of UE coordination deficits in persons with strokes is critical for better identification of motor impairment and planning for rehabilitation, it is still not clear how stroke affects coordination patterns of multi-joint movements in the UE. Here, we investigated kinematic and kinetic coordination patterns of UE after stroke during controlled passive arm movement. Methods An exoskeleton multi-joint robot moved the participant’s arm in the horizontal plane back and forth in 8 repetitions, in inward movement (i.e. toward the body) and outward movement (i.e. away from the body). The uncontrolled manifold analysis (UCM) was used to quantify kinematic and kinetic coordination patterns of the UE. Variability of joint angles and torques were decomposed into task-relevant variability (TRV) and task-irrelevant variability (TIV). An index of coordination (IC) was defined based on TRV and TIV. Results We found that the IC of joint torques in the stroke group significantly decreased during outward movement in comparison to that during inward movement, while IC of the control group showed no difference between the two movement directions. The decreased IC in the stroke group during outward movement was mainly due to the increased TRV of joint torques. In the further analysis of individual joint level, during outward movement, stroke group had a greater TRV of joint torques at all joints while during inward movement, stroke group had a lower TRV of joint torques at elbow joint. Conclusions Our results indicate that the stroke can cause the kinetic coordination deficits induced during a passive movement especially in outward movement. Our findings suggest that it is important to consider the passive kinetic coordination deficits to enhance post-stroke rehabilitation interventions. Trial registration clinicaltrials.gov, ID: NCT02359812. Registered 23 January 2015; Last Updated 06 August 2020.