Date of Award

Summer 2011

Document Type


Degree Name

Master of Science (MS)


Biomedical Engineering

First Advisor

Schmit, Brian D.

Second Advisor

Hyngstrom, Allison

Third Advisor

Beardsley, Scott


Post stroke hemiparesis causes reflex coupling in multiple muscles of the arm, leading to atypical movements that hamper motor control. In particular, people post-stroke can become unstable while holding the arm at the end of a planar motion. Recently, we have found that tendon vibration of the wrist flexors improves the stability of the arm during a hold task. The objective of the current study was to identify the effects of vibration applied to the wrist flexors on the biceps and triceps stretch reflexes, generated using a tendon tapper. In people post-stroke, tendon tap perturbations of the biceps and triceps elicit heteronymous spinal reflexes in muscles of the wrist, elbow and shoulder. We hypothesized that if tendon vibration improved stabilization of the arm through spinal reflex pathways, then heteronymous tendon tap reflexes would be modified by wrist vibration. Ten chronic stroke survivors and 5 age-matched controls participated in this study. Subjects were seated in a high-back chair, force/torque measurements were made from the 6 axis load cells at the elbow and wrist and EMG signals were recorded from 8 muscles. Isometric maximum voluntary contractions (MVCs) were performed for wrist and elbow flexion/extension and shoulder abduction/adduction. The test protocol consisted of 6 active tasks and 3 relaxed conditions in a randomized order, each consisting of 30 taps, with vibration applied during the middle 10 taps. The active tasks consisted of the same task types as the MVCs; however, the subjects maintained their primary force/torque between 10% and 30% of their MVCs. Peak-to-peak amplitude of the reflexes showed negligible changes in amplitude during vibration compared to the non vibration trials. These results showed that tendon vibration did not affect the multi-joint reflex coupling of muscles across the arm. Thus, the effects of tendon vibration as a sensory intervention, as seen in previous studies on arm stability do not appear to occur at the spinal level. These results imply that the effects of vibration on arm stability likely occur in supraspinal structures, suggesting a change in supraspinal sensorimotor integration underlies the effects.