Alterations in upper limb muscle synergy structure in chronic stroke survivors

I wish they would know how to break muscle synergy. Recovery could occur much faster if there was a specified way to defeat those synergies.
http://search.naric.com/research/rehab/redesign_record.cfm?search=2&type=all&criteria=J67535&phrase=no&rec=123301
NARIC Accession Number: J67535.  What's this?
ISSN: 0022-3077.
Author(s): Roh, Jinsook; Rymer, William Z.; Perreault, Eric J.; Yoo, Seng B.; Beer, Randall F..
Project Number: H133G060169.
Publication Year: 2013.
Number of Pages: 14.
Abstract: Study examined the structure and recruitment of muscle synergies underlying isometric force generation in severely impaired stroke survivors. Previous studies have shown that motor coordination can be described by task-dependent combinations of a few muscle synergies, defined as a fixed pattern of activation across a set of muscles. Arm function in severely impaired stroke survivors is characterized by stereotypical postural and movement patterns involving the shoulder and elbow. Accordingly, it was hypothesized that muscle synergy composition is altered in severely impaired stroke survivors. Using an isometric force matching protocol, the spatial activation patterns of elbow and shoulder muscles were examined in the affected arm of 10 stroke survivors and in both arms of 6 age-matched controls. Underlying muscle synergies were identified using non-negative matrix factorization. In both groups, muscle activation patterns could be reconstructed by combinations of a few muscle synergies (typically 4). Abnormal coupling of shoulder and elbow muscles was not found within individual muscle synergies. In stroke survivors, as in controls, two of the synergies were comprised of isolated activation of the elbow flexors and extensors. However, muscle synergies involving proximal muscles exhibited consistent alterations following stroke. Unlike controls, the anterior deltoid was coactivated with medial and posterior deltoids within the shoulder abductor/extensor synergy and the shoulder adductor/flexor synergy in stroke was dominated by activation of pectoralis major, with limited anterior deltoid activation. Recruitment of the altered shoulder muscle synergies was strongly associated with abnormal task performance. Overall, the results suggest that an impaired control of the individual deltoid heads may contribute to poststroke deficits in arm function.