Jacob G McPherson1, Arno H Stienen1, Justin M Drogos1, Julius P Dewald2. 1. Department of Physical Therapy and Human Movement Sciences, Northwestern University Feinberg School of Medicine, Chicago, IL. 2. Department of Physical Therapy and Human Movement Sciences, Northwestern University Feinberg School of Medicine, Chicago, IL; Department of Physical Medicine and Rehabilitation, Northwestern University Feinberg School of Medicine, Chicago, IL; Department of Biomedical Engineering, Northwestern University McCormick School of Engineering, Chicago, IL. Electronic address: j-dewald@northwestern.edu.
Abstract
OBJECTIVE: To systematically characterize the effect of flexion synergy expression on the manifestation of elbow flexor stretch reflexes poststroke, and to relate these findings to elbow flexor stretch reflexes in individuals without neurologic injury. DESIGN: Controlled cohort study. SETTING: Academic medical center. PARTICIPANTS: Participants (N=20) included individuals with chronic hemiparetic stroke (n=10) and a convenience sample of individuals without neurologic or musculoskeletal injury (n=10). INTERVENTIONS: Participants with stroke were interfaced with a robotic device that precisely manipulated flexion synergy expression (by regulating shoulder abduction loading) while delivering controlled elbow extension perturbations over a wide range of velocities. This device was also used to elicit elbow flexor stretch reflexes during volitional elbow flexor activation, both in the cohort of individuals with stroke and in a control cohort. In both cases, the amplitude of volitional elbow flexor preactivation was matched to that generated involuntarily during flexion synergy expression. MAIN OUTCOME MEASURES: The amplitude of short- and long-latency stretch reflexes in the biceps brachii, assessed by electromyography, and expressed as a function of background muscle activation and stretch velocity. RESULTS: Increased shoulder abduction loading potentiated elbow flexor stretch reflexes via flexion synergy expression in the paretic arm. Compared with stretch reflexes in individuals without neurologic injury, paretic reflexes were larger at rest but were approximately equal to control muscles at matched levels of preactivation. CONCLUSIONS: Because flexion synergy expression modifies stretch reflexes in involved muscles, interventions that reduce flexion synergy expression may confer the added benefit of reducing spasticity during functional use of the arm.
OBJECTIVE: To systematically characterize the effect of flexion synergy expression on the manifestation of elbow flexor stretch reflexes poststroke, and to relate these findings to elbow flexor stretch reflexes in individuals without neurologic injury. DESIGN: Controlled cohort study. SETTING: Academic medical center. PARTICIPANTS: Participants (N=20) included individuals with chronic hemiparetic stroke (n=10) and a convenience sample of individuals without neurologic or musculoskeletal injury (n=10). INTERVENTIONS:Participants with stroke were interfaced with a robotic device that precisely manipulated flexion synergy expression (by regulating shoulder abduction loading) while delivering controlled elbow extension perturbations over a wide range of velocities. This device was also used to elicit elbow flexor stretch reflexes during volitional elbow flexor activation, both in the cohort of individuals with stroke and in a control cohort. In both cases, the amplitude of volitional elbow flexor preactivation was matched to that generated involuntarily during flexion synergy expression. MAIN OUTCOME MEASURES: The amplitude of short- and long-latency stretch reflexes in the biceps brachii, assessed by electromyography, and expressed as a function of background muscle activation and stretch velocity. RESULTS: Increased shoulder abduction loading potentiated elbow flexor stretch reflexes via flexion synergy expression in the paretic arm. Compared with stretch reflexes in individuals without neurologic injury, paretic reflexes were larger at rest but were approximately equal to control muscles at matched levels of preactivation. CONCLUSIONS: Because flexion synergy expression modifies stretch reflexes in involved muscles, interventions that reduce flexion synergy expression may confer the added benefit of reducing spasticity during functional use of the arm.
Authors: Emily M Mugler; Goran Tomic; Aparna Singh; Saad Hameed; Eric W Lindberg; Jon Gaide; Murad Alqadi; Elizabeth Robinson; Katherine Dalzotto; Camila Limoli; Tyler Jacobson; Jungwha Lee; Marc W Slutzky Journal: Neurorehabil Neural Repair Date: 2019-03-19 Impact factor: 3.919
Authors: Yuan Yang; Nirvik Sinha; Runfeng Tian; Netta Gurari; Justin M Drogos; Julius P A Dewald Journal: IEEE Trans Neural Syst Rehabil Eng Date: 2020-04-07 Impact factor: 3.802
Authors: Jacob G McPherson; Laura M McPherson; Christopher K Thompson; Michael D Ellis; Charles J Heckman; Julius P A Dewald Journal: Front Hum Neurosci Date: 2018-04-09 Impact factor: 3.169
Authors: Jacob G McPherson; Michael D Ellis; R Norman Harden; Carolina Carmona; Justin M Drogos; Charles J Heckman; Julius P A Dewald Journal: Front Neurol Date: 2018-06-21 Impact factor: 4.003