Compensatory Proximal Adjustments Characterize Effective Reaching Movements After Stroke

BACKGROUND: Understanding of sensorimotor reorganization following a stroke is still incomplete. This study examined how the neuromotor system of well-recovered patients with stroke achieves stable control of the redundant degrees of freedom in the upper limb through goal-directed reaching movements. METHODS: Thirteen right-handed individuals with left-hemispheric stroke and 13 age-, sex- and handedness-matched healthy controls participated in this cross-sectional study. Each participant performed 80 unconstrained reach-to-grasp movements with either arm while kinematic data were recorded at 200 Hz using an optoelectronic motion capture system. Two types of outcome measures were examined, contrasting healthy individuals with those who have had strokes: end point and proximal kinematics. End point kinematics analyzed spatiotemporal hand movement characteristics, including movement time, time-to-peak velocity (TTPVHD), time-to-peak acceleration (TTPAHD), and velocity peaks for trajectory smoothness. Proximal kinematics focused on interjoint and intrajoint coordination of the elbow and shoulder, examining angular velocities and their timing differences. Stroke effects were analyzed using linear mixed-effects models. RESULTS: No significant differences were observed in distal end point kinematics between groups (n=13 each) for movement time (control versus stroke, 0.92 versus 0.96 s; P=0.944), TTPVHD (40% versus 42% of movement time, P=0.358), TTPAHD (22% versus 21%; P=0.583), or smoothness (1.02 versus 1.15; P=0.057). However, stroke significantly affected proximal kinematics, altering interjoint coordination with differences in timing between elbow flexion and shoulder rotation (18% versus 14%; P=0.019) and intrajoint coordination with differences in timing between shoulder flexion and abduction (18% versus 11%; P=0.008) and between flexion and rotation (1% versus 10%; P=0.001). CONCLUSIONS: Arm motor control in this cohort of well-recovered patients with stroke showed near-complete restoration of distal end point kinematics but significant differences in the timing of proximal intrajoint and interjoint coordination. These findings suggest compensatory adjustments in shoulder and elbow movements to achieve functional goals like reaching. An enhanced understanding of these strategies can inform targeted interventions to improve upper limb capability poststroke.