On the Origin of Muscle Synergies: Invariant Balance in the Co-activation of Agonist and Antagonist Muscle Pairs
Name
Hirai-2015-On the Origin of Mus.pdf
Size
3.34 MB
Format
Adobe PDF
Checksum (MD5)
f221778d74616037d94ea2aa07e920ce
Author(s)
Hirai, Hiroaki
Miyazaki, Fumio
Naritomi, Hiroaki
Koba, Keitaro
Oku, Takanori
Uno, Kanna
Uemura, Mitsunori
Nishi, Tomoki
Kageyama, Masayuki
Krebs, Hermano Igo
Date Issued
November 2015
Journal
Frontiers in Bioengineering and Biotechnology
Publisher
Frontiers Research Foundation
Citation
Hirai, Hiroaki, Fumio Miyazaki, Hiroaki Naritomi, Keitaro Koba, Takanori Oku, Kanna Uno, Mitsunori Uemura, Tomoki Nishi, Masayuki Kageyama, and Hermano Igo Krebs. “On the Origin of Muscle Synergies: Invariant Balance in the Co-Activation of Agonist and Antagonist Muscle Pairs.” Frontiers in Bioengineering and Biotechnology 3 (November 24, 2015).
Version
Final published version
Abstract
Investigation of neural representation of movement planning has attracted the attention of neuroscientists, as it may reveal the sensorimotor transformation essential to motor control. The analysis of muscle synergies based on the activity of agonist–antagonist (AA) muscle pairs may provide insight into such transformations, especially for a reference frame in the muscle space. In this study, we examined the AA concept using the following explanatory variables: the AA ratio, which is related to the equilibrium-joint angle, and the AA sum, which is associated with joint stiffness. We formulated muscle synergies as a function of AA sums, positing that muscle synergies are composite units of mechanical impedance. The AA concept can be regarded as another form of the equilibrium-point (EP) hypothesis, and it can be extended to the concept of EP-based synergies. We introduce, here, a novel tool for analyzing the neurological and motor functions underlying human movements and review some initial insights from our results about the relationships between muscle synergies, endpoint stiffness, and virtual trajectories (time series of EP). Our results suggest that (1) muscle synergies reflect an invariant balance in the co-activation of AA muscle pairs; (2) each synergy represents the basis for the radial, tangential, and null movements of the virtual trajectory in the polar coordinates centered on the specific joint at the base of the body; and (3) the alteration of muscle synergies (for example, due to spasticity or rigidity following neurological injury) results in significant distortion of endpoint stiffness and concomitant virtual trajectories. These results indicate that muscle synergies (i.e., the balance of muscle mechanical impedance) are essential for motor control.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
Terms of Use
Creative Commons Attribution
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.3389/fbioe.2015.00192
