scholarly journals Cortical control of locomotor muscle activity through muscle synergies in humans: a neural decoding study

2018 ◽  
Author(s):  
Hikaru Yokoyama ◽  
Naotsugu Kaneko ◽  
Tetsuya Ogawa ◽  
Noritaka Kawashima ◽  
Katsumi Watanabe ◽  
...  
Keyword(s):  
Muscle Activity ◽  
Muscle Activation ◽  
Indirect Evidence ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Neural Decoding ◽  
Individual Muscle ◽  
Cortical Involvement ◽  
Decoding Accuracy

AbstractWalking movements are orchestrated by the activation of a large number of muscles. The control of numerous muscles during walking is believed to be simplified by flexible activation of groups of muscles called muscle synergies. Although significant corticomuscular connectivity during walking has been reported, the level at which the cortex controls locomotor muscle activity (i.e., muscle synergy or individual muscle level) remains unclear. Here, we examined cortical involvement in muscle control during walking by brain decoding of the activation of muscle synergies and individual muscles from electroencephalographic (EEG) signals using linear decoder models. First, we demonstrated that activation of locomotor muscle synergies was decoded from slow cortical waves with significant accuracy. In addition, we found that decoding accuracy for muscle synergy activation was greater than that for individual muscle activation and that decoding of individual muscle activation was based on muscle synergy-related cortical information. Taken together, these results provide indirect evidence that the cerebral cortex hierarchically controls multiple muscles through a few muscle synergies during walking. Our findings extend the current understanding of the role of the cortex in muscular control during walking and could accelerate the development of effective brain-machine interfaces for people with locomotor disabilities.

scholarly journals Alterations in upper limb muscle synergy structure in chronic stroke survivors

2013 ◽  
Vol 109 (3) ◽  
pp. 768-781 ◽  
Author(s):  
Jinsook Roh ◽  
William Z. Rymer ◽  
Eric J. Perreault ◽  
Seng Bum Yoo ◽  
Randall F. Beer
Keyword(s):  
Muscle Activation ◽  
Isometric Force ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Stroke Survivors ◽  
Activation Patterns ◽  
Force Matching ◽  
Muscle Activation Patterns ◽  
Anterior Deltoid ◽  
Arm Function

Previous studies in neurologically intact subjects have shown that motor coordination can be described by task-dependent combinations of a few muscle synergies, defined here 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, we hypothesized that muscle synergy composition is altered in severely impaired stroke survivors. Using an isometric force matching protocol, we examined the spatial activation patterns of elbow and shoulder muscles in the affected arm of 10 stroke survivors (Fugl-Meyer <25/66) and in both arms of six 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). We did not find abnormal coupling of shoulder and elbow muscles 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, our results suggest that an impaired control of the individual deltoid heads may contribute to poststroke deficits in arm function.

scholarly journals Subject-Specific Muscle Synergies in Human Balance Control Are Consistent Across Different Biomechanical Contexts

2010 ◽  
Vol 103 (6) ◽  
pp. 3084-3098 ◽  
Author(s):  
Gelsy Torres-Oviedo ◽  
Lena H. Ting
Keyword(s):  
Muscle Activation ◽  
Balance Control ◽  
Nonnegative Matrix ◽  
The Body ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Support Surface ◽  
Activation Patterns ◽  
Muscle Activation Patterns ◽  
Specific Muscle

The musculoskeletal redundancy of the body provides multiple solutions for performing motor tasks. We have proposed that the nervous system solves this unconstrained problem through the recruitment of motor modules or functional muscle synergies that map motor intention to action. Consistent with this hypothesis, we showed that trial-by-trial variations in muscle activation for multidirectional balance control in humans were constrained by a small set of muscle synergies. However, apparent muscle synergy structures could arise from characteristic patterns of sensory input resulting from perturbations or from low-dimensional optimal motor solutions. Here we studied electromyographic (EMG) responses for balance control across a range of biomechanical contexts, which alter not only the sensory inflow generated by postural perturbations, but also the muscle activation patterns used to restore balance. Support-surface translations in 12 directions were delivered to subjects standing in six different postural configurations: one-leg, narrow, wide, very wide, crouched, and normal stance. Muscle synergies were extracted from each condition using nonnegative matrix factorization. In addition, muscle synergies from the normal stance condition were used to reconstruct muscle activation patterns across all stance conditions. A consistent set of muscle synergies were recruited by each subject across conditions. When balance demands were extremely different from the normal stance (e.g., one-legged or crouched stance), task-specific muscle synergies were recruited in addition to the preexisting ones, rather generating de novo muscle synergies. Taken together, our results suggest that muscle synergies represent consistent motor modules that map intention to action, regardless of the biomechanical context of the task.

Individual Muscle Control Using an Exoskeleton Robot for Muscle Function Testing

2009 ◽  
Author(s):  
Jun Ueda ◽  
Moiz Hyderabadwala ◽  
Ming Ding ◽  
Tsukasa Ogasawara ◽  
Vijaya Krishnamoorthy ◽  
...  
Keyword(s):  
Muscle Activity ◽  
Muscle Function ◽  
Muscle Activation ◽  
Muscle Control ◽  
Wearable Robot ◽  
Activity Data ◽  
Individual Muscle ◽  
Exoskeleton Robot ◽  
Function Tests ◽  
Function Testing

A functionality test at the level of individual muscles by investigating the activity of a muscle of interest on various tasks may enable muscle-level force grading. This paper proposes a new method for muscle function tests using an exoskeleton robot for obtaining a wider variety of muscle activity data than standard motor tasks, e.g., pushing a handle by his/her hand. A computational algorithm systematically computes control commands to a wearable robot with actuators (an exoskeleton robot, or a power-assisting device) so that a desired muscle activation pattern for target muscle forces is induced. This individual muscle control method enables users (e.g., therapists) to efficiently conduct neuromuscular function tests for target muscles by arbitrarily inducing muscle activation patterns. Simulation results justify the use of an exoskeleton robot for muscle function testing in terms of the variety of muscle activity data.

scholarly journals When 90% of the variance is not enough: residual EMG from muscle synergy extraction influences task performance

2019 ◽  
Author(s):  
Victor R. Barradas ◽  
Jason J. Kutch ◽  
Toshihiro Kawase ◽  
Yasuharu Koike ◽  
Nicolas Schweighofer
Keyword(s):  
Motor Control ◽  
Dimensionality Reduction ◽  
Muscle Activity ◽  
Muscle Force ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Systematic Effect ◽  
Extraction Techniques ◽  
Force Mapping ◽  
Variance Explained

AbstractMuscle synergies are usually identified via dimensionality reduction techniques, such that the identified synergies reconstruct the muscle activity to a level of accuracy defined heuristically, such as 90% of the variance explained. Here, we question the assumption that the residual muscle activity not explained by the synergies is due to noise. We hypothesize instead that the residual activity is structured and can therefore influence the execution of a motor task. Young healthy subjects performed an isometric reaching task in which surface electromyography of 10 arm muscles was mapped onto estimated two-dimensional forces used to control a cursor. Three to five synergies were extracted to account for 90% of the variance explained. We then altered the muscle-force mapping via “hard” and “easy” virtual surgeries. Whereas in both surgeries the forces associated with synergies spanned the same single dimension of the virtual environment, the muscle-force mapping was as close as possible to the initial mapping in the easy surgery and as far as possible in the hard surgery. This design therefore maximized potential differences in reaching errors attributable to the residual muscle activity. Results show that the easy surgery produced much smaller directional errors than the hard task. In addition, systematic estimations of the errors for easy and hard surgeries constructed with 1 to 10 synergies show that the errors differ significantly for up to 8 synergies, which account for 98% of the variance on average. Our study therefore indicates the need for cautious interpretations of results derived from synergy extraction techniques based on heuristics with lenient levels of accuracy.Author summaryThe muscle synergy hypothesis states that the central nervous system simplifies motor control by grouping muscles that share common functions into modules called muscle synergies. Current techniques use unsupervised dimensionality reduction algorithms to identify these synergies. However, these techniques rely on arbitrary criteria to determine the number of synergies, which is actually unknown. An example of such criteria is that the identified synergies must be able to reconstruct the measured muscle activity to at least a 90% level of accuracy. Thus, the residual muscle activity, the remaining 10% of the muscle activity, is often disregarded as noise. We show that residual muscle activity following muscle synergy identification has a large systematic effect on movements even when the number of synergies approaches the number of muscles. This suggests that current synergy extraction techniques may discard a component of muscle activity that is important for motor control. Therefore, current synergy extraction techniques must be updated to identify true physiological synergies.

scholarly journals Lower-limb muscle function is influenced by changing mechanical demands in cycling

2020 ◽  
pp. jeb.228221
Author(s):  
Adrian K. M. Lai ◽  
Taylor J. M. Dick ◽  
Nicholas A. T. Brown ◽  
Andrew A. Biewener ◽  
James M. Wakeling
Keyword(s):  
Lower Limb ◽  
Muscle Activity ◽  
Muscle Function ◽  
Muscle Activation ◽  
Functional Index ◽  
Lower Limb Muscles ◽  
Wide Range ◽  
Musculoskeletal Simulations ◽  
Contractile Performance

Although cycling is often considered a seemingly simple, reciprocal task, muscles must adapt their function to satisfy changes in mechanical demands induced by higher crank torques and faster pedalling cadences. We examined if muscle function was sensitive to these changes in mechanical demands across a wide range of pedalling conditions. We collected experimental data of cycling where crank torque and pedalling cadence were independently varied from 13-44 Nm and 60-140 RPM. These data were used in conjunction with musculoskeletal simulations and a recently developed functional index-based approach to characterise the role of the human lower-limb muscles. We found that in muscles that generate most of the mechanical power and work during cycling, greater crank torque induced shifts towards greater muscle activation, greater positive muscle-tendon unit (MTU) work and a more motor-like function, particularly in the limb extensors. Conversely, with faster pedalling cadence, the same muscles exhibited a phase advance in muscle activity prior to crank top dead centre, which led to greater negative MTU power and work and shifted the muscles to contract with more spring-like behaviour. Our results illustrate the capacity for muscles to adapt their function to satisfy the mechanical demands of the task, even during highly constrained reciprocal tasks such as cycling. Understanding how muscles shift their contractile performance under varied mechanical and environmental demands may inform decisions on how to optimise pedalling performance and to design targeted cycling rehabilitation therapies for muscle-specific injuries or deficits.

Muscle Synergies Based on a Biomechanical Biaxial Isometric Shoulder Model Minimizing Fatigue

2010 ◽  
Author(s):  
Mohamadreza Nassajian Moghadam ◽  
Kamiar Aminian ◽  
Mohsen Asghari ◽  
Mohammad Parnianpour
Keyword(s):  
Shoulder Joint ◽  
Degrees Of Freedom ◽  
Muscle Activation ◽  
Glenohumeral Joint ◽  
Nonnegative Matrix ◽  
Factorization Method ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Specific Direction ◽  
Activation Data

In this study we utilize the concept of synergy formation as a simplifying control strategy to manage the high number of degrees of freedom presented in the maintenance of the posture of the shoulder joint. We address how to find the muscle synergy recruitment map to the biomechanical demands (biaxial external torque) during an isometric shoulder task. We use a numerical optimization based shoulder model to obtain muscle activation levels when a biaxial external isometric torque is exposed at the shoulder glenohumeral joint. In the numerical simulations, different shoulder torque vectors parallel to the horizontal plane are considered. For each selected direction for the torque, the resulting muscle activation data are calculated and then used for grouping muscles in some fixed element synergies by nonnegative matrix factorization method Next, the muscle synergies are converted from activation level to the torque space to see how muscle synergy recruitment addresses the torque production in a specific direction at the shoulder joint. The results confirmed our expectation that the few dominant synergies are sufficient to address the torque vectors in directions which coincide to the basic vectors of torque space, such that each muscle contributed to more than one synergy.

Effects of Gravity on Velopharyngeal Muscle Activity during Speech

1995 ◽  
Vol 32 (5) ◽  
pp. 371-375 ◽  
Author(s):  
Jerald B. Moon ◽  
John W. Canady
Keyword(s):  
Motor Control ◽  
Muscle Activity ◽  
Muscle Activation ◽  
Body Position ◽  
Significant Group ◽  
Body Postures ◽  
Levator Veli Palatini ◽  
Gravity Effects ◽  
Velopharyngeal Function

Assessment of the role of gravitational forces in the motor control of the velopharyngeal mechanism was the focus of this study. Specifically, the effect of gravity on activation levels of the levator veli palatini and palatoglossus muscles was assessed. Nineteen volunteers repeated a CV syllable in upright and supine body positions. Overall, lower peak activation levels of levator veli palatini were observed in the supine body position. The results suggest that less muscle activity was seen in the levator veli palatini in the supine body posture, where gravitational effects worked in the same direction (i.e., toward closure). No statistically significant group effects were seen in muscle activation levels of palatoglossus across the two body postures, although clear gravity effects were observed in some subjects. The implications of these findings from a speech motor control perspective are discussed in relation to normal and disordered velopharyngeal function.

Muscular and Postural Synergies of the Human Hand

2004 ◽  
Vol 92 (1) ◽  
pp. 523-535 ◽  
Author(s):  
Erica J. Weiss ◽  
Martha Flanders
Keyword(s):  
Muscle Activation ◽  
Human Subjects ◽  
Motor Units ◽  
Muscle Synergy ◽  
Human Hand ◽  
Muscle Synergies ◽  
Global Pattern ◽  
Hand Muscles ◽  
Multimodal Function ◽  
Postural Synergies

Because humans have limited ability to independently control the many joints of the hand, a wide variety of hand shapes can be characterized as a weighted combination of just two or three main patterns of covariation in joint rotations, or “postural synergies.” The present study sought to align muscle synergies with these main postural synergies and to describe the form of membership of motor units in these postural/muscle synergies. Seventeen joint angles and the electromyographic (EMG) activities of several hand muscles (both intrinsic and extrinsic muscles) were recorded while human subjects held the hand statically in 52 specific shapes (i.e., shaping the hand around 26 commonly grasped objects or forming the 26 letter shapes of a manual alphabet). Principal-components analysis revealed several patterns of muscle synergy, some of which represented either coactivation of all hand muscles, or reciprocal patterns of activity (above and below average levels) in the intrinsic index finger and thumb muscles or (to a lesser extent) in the extrinsic four-tendoned extensor and flexor muscles. Single- and multiunit activity was generally a multimodal function of whole hand shape. This implies that motor-unit activation does not align with a single synergy; instead, motor units participate in multiple muscle synergies. Thus it appears that the organization of the global pattern of hand muscle activation is highly distributed. This organization mirrors the highly fractured somatotopy of cortical hand representations and may provide an ideal substrate for motor learning and recovery from injury.

scholarly journals Absence of postural muscle synergies for balance after spinal cord transection

2013 ◽  
Vol 110 (6) ◽  
pp. 1301-1310 ◽  
Author(s):  
Stacie A. Chvatal ◽  
Jane M. Macpherson ◽  
Gelsy Torres-Oviedo ◽  
Lena H. Ting
Keyword(s):  
Spinal Cord ◽  
Muscle Activity ◽  
Balance Control ◽  
Neural Mechanisms ◽  
Spinal Cord Transection ◽  
Muscle Synergy ◽  
Modular Organization ◽  
Muscle Synergies ◽  
Weight Support ◽  
Postural Muscle

Although cats that have been spinalized can also be trained to stand and step with full weight support, directionally appropriate long-latency responses to perturbations are impaired, suggesting that these behaviors are mediated by distinct neural mechanisms. However, it remains unclear whether these responses reflect an attenuated postural response using the appropriate muscular coordination patterns for balance or are due to fundamentally different neural mechanisms such as increased muscular cocontraction or short-latency stretch responses. Here we used muscle synergy analysis on previously collected data to identify whether there are changes in the spatial organization of muscle activity for balance within an animal after spinalization. We hypothesized that the modular organization of muscle activity for balance control is disrupted by spinal cord transection. In each of four animals, muscle synergies were extracted from postural muscle activity both before and after spinalization with nonnegative matrix factorization. Muscle synergy number was reduced after spinalization in three animals and increased in one animal. However, muscle synergy structure was greatly altered after spinalization with reduced direction tuning, suggesting little consistent organization of muscle activity. Furthermore, muscle synergy recruitment was correlated to subsequent force production in the intact but not spinalized condition. Our results demonstrate that the modular structure of sensorimotor feedback responses for balance control is severely disrupted after spinalization, suggesting that the muscle synergies for balance control are not accessible by spinal circuits alone. Moreover, we demonstrate that spinal mechanisms underlying weight support are distinct from brain stem mechanisms underlying directional balance control.

Function of the Thyroarytenoid Muscle in a Canine Laryngeal Model

1993 ◽  
Vol 102 (10) ◽  
pp. 769-776 ◽  
Author(s):  
Hong-Shik Choi ◽  
Ming Ye ◽  
Gerald S. Berke ◽  
Jody Kreiman
Keyword(s):  
Muscle Activity ◽  
High Frequency ◽  
Vocal Fold ◽  
Muscle Activation ◽  
Thyroid Cartilage ◽  
Vocal Folds ◽  
Vocal Fold Vibration ◽  
Thyroarytenoid Muscle

Fundamental frequency is controlled by contraction of the thyroarytenoid (TA) and cricothyroid (CT) muscles. While activity of the CT muscle is known to tense and thin the vocal folds, little is known about the effect of the TA muscle on vocal fold vibration. An in vivo canine laryngeal model was used to examine the role of the TA muscle in controlling phonation. Isolated TA muscle activation was obtained by stimulating sectioned terminal TA branches through small thyroid cartilage windows. Subglottic pressure measures, electroglottographic and photoglottographic signals, and acoustic signals were obtained in 5 mongrel dogs during dynamic and static variations in TA muscle activity. Results indicated that TA muscle activation is a major determinant in sudden shifts from high-frequency to modal phonation. Subglottic pressure increased and open quotient decreased gradually with increasing TA activation.

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