Muscle inhibition following tendon stimulation is reduced in chronic stroke

ObjectiveElectrical tendon stimulation elicits reflex inhibition in the homonymous muscle that is thought to be mediated by group III afferents. The study goals were to: evaluate group III-mediated reflex inhibition in people with post-stroke hemiparesis; determine the presence of heteronymous group III pathways; investigate the relevance of reflex inhibition to arm function.MethodsReflex responses were recorded in wrist, elbow, and shoulder muscles following stimulation of the extensor carpi radialis (ECR) tendon in 16 people with post-stroke hemiparesis and 16 control subjects. In control subjects, reflex inhibition also was compared between static and dynamic muscle activation.ResultsReflex inhibition following ECR tendon stimulation was present in heteronymous muscles of most, but not all, stroke and control subjects. The level of reflex inhibition was significantly reduced in stroke subjects. In the controls, reflex inhibition was greater during dynamic activation of elbow muscles compared to static activation.ConclusionsEvidence that reflex inhibition projects to heteronymous muscles and is modulated during movement suggests a role for the reflex in multi-joint coordination. The reflex is impaired in post-stroke hemiparesis.SignificanceAbnormalities in the regulation of group III-mediated muscle inhibition in the stroke population may contribute to impaired muscle activation patterns during movement.