Abnormal muscle coactivation patterns during isometric torque generation at the elbow and shoulder in hemiparetic subjects

To study abnormal spatial patterns of muscle activation in hemiparetic stroke, we compared EMG activity in paretic and contralateral elbow and shoulder muscles of 10 hemiparetic subjects during 1.5-s voluntary isometric contractions, against five to eight different loads. Isometric forces were gener...

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Veröffentlicht in:Brain (London, England : 1878) England : 1878), 1995-04, Vol.118 (2), p.495-510
Hauptverfasser: Dewald, Julius P. A., Pope, Patrick S., Given, Joseph D., Buchanan, Thomas S., Rymer, W. Zev
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container_issue 2
container_start_page 495
container_title Brain (London, England : 1878)
container_volume 118
creator Dewald, Julius P. A.
Pope, Patrick S.
Given, Joseph D.
Buchanan, Thomas S.
Rymer, W. Zev
description To study abnormal spatial patterns of muscle activation in hemiparetic stroke, we compared EMG activity in paretic and contralateral elbow and shoulder muscles of 10 hemiparetic subjects during 1.5-s voluntary isometric contractions, against five to eight different loads. Isometric forces were generated in eight directions, referenced to a plane orthogonal to the long axis of the forearm, and were recorded by a three degrees of freedom load cell, mounted at the wrist. Surface and intramuscular EMGs of six elbow and six shoulder muscles were recorded from both impaired and contralateral upper extremities of each subject. The spatial characteristics of EMG activation of individual muscles were summarized using two measures. The first, called the ‘net resultant EMG vector’ is a new measure which calculated the vector sum of EMG magnitudes for each of the eight directions, and the second, index of EMG focus, is a measure of the range of EMG activation recorded for each load level. Use of these measures permitted us to describe spatial EMG characteristics quantitatively, which has not been done previously. We observed consistent and statistically significant shifts in the resultant EMG vector directions in the impaired limb, especially in shoulder and other proximal muscles. Significant increases in the angular range of EMG activity were also identified and were most evident at the elbow. Correlation analysis techniques were used to assess the degree of coactivation of different muscle pairs. There were consistent EMG coactivation patterns observed across all subjects (both normal and hemiparetic). However, in spastic-paretic limbs, additional novel coactivational relationships were also recorded, especially between elbow flexors/shoulder abductors and elbow extensors/shoulder adductors. These novel coactivation patterns represent a reduction in the number of possible muscle combinations, or in the number of possible ‘synergies’ in the paretic limb of the stroke subject. This reduction in number of ‘synergies’ could result from a loss of descending command options; from an increased reliance on residual, descending brainstem pathways (such as the reticulospinal and vestibulospinal projections); from changes in spinal interneuronal excitability; or from a combination of several of these factors. The relative merits of these hypotheses are addressed.
doi_str_mv 10.1093/brain/118.2.495
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This reduction in number of ‘synergies’ could result from a loss of descending command options; from an increased reliance on residual, descending brainstem pathways (such as the reticulospinal and vestibulospinal projections); from changes in spinal interneuronal excitability; or from a combination of several of these factors. The relative merits of these hypotheses are addressed.</abstract><cop>Oxford</cop><pub>Oxford University Press</pub><pmid>7735890</pmid><doi>10.1093/brain/118.2.495</doi><tpages>16</tpages></addata></record>
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identifier ISSN: 0006-8950
ispartof Brain (London, England : 1878), 1995-04, Vol.118 (2), p.495-510
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language eng
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source Oxford University Press Journals Digital Archive legacy; MEDLINE
subjects Adult
Aged
Biological and medical sciences
Cerebrovascular Disorders - complications
Cerebrovascular Disorders - physiopathology
Elbow
Electromyography
EMG
Hemiplegia - etiology
Hemiplegia - physiopathology
Humans
Isometric Contraction
Medical sciences
Middle Aged
Muscle Spasticity - physiopathology
muscle synergies
Neurology
Shoulder
static posture
stroke
upper extremity
Vascular diseases and vascular malformations of the nervous system
title Abnormal muscle coactivation patterns during isometric torque generation at the elbow and shoulder in hemiparetic subjects
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