Extraction and implementation of muscle synergies in hand-force control

Pham, Hang; Kimura, M.; Hirai, Hiroaki; Miyazaki, Fumio

doi:10.1109/icra.2011.5979839

Cited by 14 publications

(19 citation statements)

References 7 publications

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“…As seen in this figure, the PC scores all go around a central point, just as the generated hand forces do. Note that the PC scores of the left hand are almost the same as those of the right hand at symmetric positions, reflecting the fact that the left and right arm postures are symmetric (Pham et al 2011). Since the shape of the PC scores resembles the circle-like shape of the hand force, a high correlation between PC scores and hand force is expected.…”

Section: Pca Resultsmentioning

confidence: 90%

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Motor Control Based on the Muscle Synergy Hypothesis

Hirai

Pham

Ariga

et al. 2016

Cognitive Neuroscience Robotics A

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In neuroscience, the idea that motor behaviors are constructed by a combination of building blocks has been supported by a large amount of experimental evidences. The idea has been very attractive as a powerful strategy for solving the motor redundancy problem. While there are some candidates for motor primitives, such as submovements, oscillations, and mechanical impedances, synergies are one of the candidates for motor modules or composite units for motor control. Synergies are usually extracted by applying statistic techniques to explanatory variables, such as joint angles and electromyography (EMG) signals, and by decomposing these variables into fewer units. The results of factor decomposition are, however, not necessarily interpretable with these explanatory variables, even though the factors successfully reduce the dimensionality of movement; therefore, the physical meaning of synergies is unclear in most cases. To obtain insight into the meaning of synergies, this chapter proposes the agonist-antagonist musclepair (A-A) concept and uses other explanatory variables: the A-A ratio, which is related to the equilibrium point (EP), and the A-A sum, which is associated with mechanical stiffness. The A-A concept can be regarded as a form comparable to the EP hypothesis (EPH, model), and it can be extended to the novel concept of EP-based synergies. These explanatory variables enable us to identify muscle synergies from human EMG signals and to interpret the physical meaning of the extracted muscle synergies. This chapter introduces the EMG analysis in hand-force generation of a human upper limb and shows that the endpoint (hand) movement is governed by two muscle synergies for (1) radial movement generation and (2) angular movement generation in a polar coordinate system centered on the shoulder joint. On the basis of the analysis, a synergy-based framework of human motor control is hypothesized, and it can explain the mechanism of the movement control in a simple way.

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Section: Pca Resultsmentioning

confidence: 90%

“…The second half of this chapter is modified from the original (Pham et al 2014), with kind permission from Taylor & Francis.…”

Section: Acknowledgementsmentioning

confidence: 99%

Motor Control Based on the Muscle Synergy Hypothesis

Hirai

Pham

Ariga

et al. 2016

Cognitive Neuroscience Robotics A

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“…3(b). Here, we made the following three assumptions: (1) a muscle can be described as a spring system whose elastic coefficient and natural length are adjusted according to EMG signal [6]; (2) the same moment arm d of each joint is constant; and (3) the upper arm and forearm have same length L.…”

Section: B Protocolmentioning

confidence: 99%

“…2) Muscle synergies: The AA muscle pair ratio (AA ratio) r i and AA muscle pair sum (AA sum) s i are defined using muscle activity m i as [6] …”

Section: B Protocolmentioning

confidence: 99%

“…To clarify the tacit representation of muscle group activities in voluntary/involuntary movements, we have analyzed the coordination between agonist-antagonist (AA) muscles and proposed the concepts of the ratio of the EMG levels of AA muscles (AA ratio) and the sum of the EMG levels of AA muscles (AA sum) [6]. On the basis of the statistical analysis of AA muscles' activities, we found that the upperlimb movements in a horizontal plane could be explained by two muscle synergies that respectively represent the bases for the radial and angular movements of an endpoint in the polar coordinates centered on the shoulder.…”

Section: Introductionmentioning

confidence: 99%

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Pilot study on quantitative assessment of muscle imbalance: Differences of muscle synergies, equilibrium-point trajectories, and endpoint stiffness in normal and pathological upper-limb movements

Oku

Uno

Nishi³

et al. 2014

2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society

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This paper proposes a novel method for assessment of muscle imbalance based on muscle synergy hypothesis and equilibrium point (EP) hypothesis of motor control. We explain in detail the method for extracting muscle synergies under the concept of agonist-antagonist (AA) muscle pairs and for estimating EP trajectories and endpoint stiffness of human upper limbs in a horizontal plane using an electromyogram. The results of applying this method to the reaching movement of one normal subject and one hemiplegic subject suggest that (1) muscle synergies (the balance among coactivation of AA muscle pairs), particularly the synergies that contributes to the angular directional kinematics of EP and the limb stiffness, are quite different between the normal subject and the hemiplegic subject; (2) the concomitant EP trajectory is also different between the normal and hemiplegic subjects, corresponding to the difference of muscle synergies; and (3) the endpoint (hand) stiffness ellipse of the hemiplegic subject becomes more elongated and orientation of the major axis rotates clockwise more than that of the normal subject. The level of motor impairment would be expected to be assessed from a comparison of these differences of muscle synergies, EP trajectories, and endpoint stiffness among normal and pathological subjects using the method.

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Forelimb force direction and magnitude independently controlled by spinal modules in the macaque

Yaron

Kowalski

Yaguchi

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Modular organization of the spinal motor system is thought to reduce the cognitive complexity of simultaneously controlling the large number of muscles and joints in the human body. Although modular organization has been confirmed in the hindlimb control system of several animal species, it has yet to be established in the forelimb motor system or in primates. Expanding upon experiments originally performed in the frog lumbar spinal cord, we examined whether costimulation of two sites in the macaque monkey cervical spinal cord results in motor activity that is a simple linear sum of the responses evoked by stimulating each site individually. Similar to previous observations in the frog and rodent hindlimb, our analysis revealed that in most cases (77% of all pairs) the directions of the force fields elicited by costimulation were highly similar to those predicted by the simple linear sum of those elicited by stimulating each site individually. A comparable simple summation of electromyography (EMG) output, especially in the proximal muscles, suggested that this linear summation of force field direction was produced by a spinal neural mechanism whereby the forelimb motor output recruited by costimulation was also summed linearly. We further found that the force field magnitudes exhibited supralinear (amplified) summation, which was also observed in the EMG output of distal forelimb muscles, implying a novel feature of primate forelimb control. Overall, our observations support the idea that complex movements in the primate forelimb control system are made possible by flexibly combined spinal motor modules.

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Extraction and implementation of muscle synergies in hand-force control

Cited by 14 publications

References 7 publications

Motor Control Based on the Muscle Synergy Hypothesis

Motor Control Based on the Muscle Synergy Hypothesis

Pilot study on quantitative assessment of muscle imbalance: Differences of muscle synergies, equilibrium-point trajectories, and endpoint stiffness in normal and pathological upper-limb movements

Forelimb force direction and magnitude independently controlled by spinal modules in the macaque

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