Stretch Reflex Excitability Quantification in Elbow and Shoulder Using a Haptic Robot

To study stretch reflex hyperexcitability and modulation in chronic hemiparetic stroke, we applied ramp-and-hold perturbations during functional multijoint movements with an admittance controlled haptic robot, the NACT-3D. We tested stretch reflex modulation through a combination of movement directions, perturbation directions, and shoulder abduction/adduction loading. Data collection is underway, with preliminary results suggesting greater reflexive EMG in antagonist muscles for a given movement on the paretic side compared to the non-paretic side. Additionally, we expect to show that stretch reflexes of shoulder muscles trigger abnormal reflexes in distal elbow muscles, following the typical pattern of the flexion synergy. Loss of supraspinal mediation of reciprocal inhibition and motor unit excitability is a likely cause. These results highlight stretch reflex hyperexcitability as a detrimental motor control impairment during movement when participants interact with unpredictable and disruptive elements of their environment.