Paper Info
Title
Empirical Evaluation of Voluntarily Activatable Muscle Synergies.
Abstract
The muscle synergy hypothesis assumes that individual muscle synergies are independent of each other and voluntarily controllable. However, this assumption has not been empirically tested. This study tested if human subjects can voluntarily activate individual muscle synergies extracted by non-negative matrix factorization (N-MF), the standard mathematical method for synergy extraction. We defined the activation of a single muscle synergy as the generation of a muscle activity pattern vector parallel to the single muscle synergy vector. Subjects performed an isometric force production task with their right hand, and the 13 muscle activity patterns associated with their elbow and shoulder movements were measured. We extracted muscle synergies during the task using electromyogram (E-MG) data and the NMF method with varied numbers of muscle synergies. The number (N) of muscle synergies was determined by using the variability accounted for (VAF, N-VAF) and the coefficient of determination (CD, N-CD). An additional muscle synergy model with N-AD was also considered. We defined a conventional muscle synergy as the muscle synergy extracted by the NVAF, N-CD, and N-AD. We also defined an extended muscle synergy as the muscle synergy extracted by the NEX>N-AD. To examine whether the individual muscle synergy was voluntarily activatable or not, we calculated the index of independent activation, which reflects similarities between a selected single muscle synergy and the current muscle activation pattern of the subject. Subjects were visually feed-backed the index of independent activation, then instructed to generate muscle activity patterns similar to the conventional and extended muscle synergies. As a result, an average of 90.8% of the muscle synergy extracted by the N-VAF was independently activated. However, the proportion of activatable muscle synergies extracted by N-CD and N-AD was lower. These results partly support the assumption of the muscle synergy hypothesis, i.e., that the conventional method can extract voluntarily and independently activatable muscle synergies by using the appropriate index of reconstruction. Moreover, an average of 25.5% of the extended muscle synergy was significantly activatable. This result suggests that the CNS can use extended muscle synergies to perform voluntary movements.
Year
DOI
Venue
2017
10.3389/fncom.2017.00082
FRONTIERS IN COMPUTATIONAL NEUROSCIENCE
Keywords
Field
DocType
muscle synergies,non-negative matrix factorization,isometric force production,electromyography,motor primitive
Muscle activity,Neuroscience,Computer science,Electromyography,Muscle activation,Isometric exercise
Journal
Volume
ISSN
Citations 
11
1662-5188
0
PageRank 
References 
Authors
0.34
9
2
Name
Order
Citations
PageRank
Shunta Togo126.05
Hiroshi Imamizu2396.50