scholarly journals Intra-Subject and Inter-Subject Movement Variability Quantified with Muscle Synergies in Upper-Limb Reaching Movements

Biomimetics ◽  
2021 ◽  
Vol 6 (4) ◽  
pp. 63
Author(s):  
Kunkun Zhao ◽  
Zhisheng Zhang ◽  
Haiying Wen ◽  
Alessandro Scano
Keyword(s):  
Muscle Synergy ◽  
Reaching Movements ◽  
Muscle Synergies ◽  
Crucial Aspect ◽  
Movement Variability ◽  
Control Structures ◽  
Subject Variability ◽  
Valuable Method ◽  
Laboratory Investigations ◽  
Function Assessment

Quantifying movement variability is a crucial aspect for clinical and laboratory investigations in several contexts. However, very few studies have assessed, in detail, the intra-subject variability across movements and the inter-subject variability. Muscle synergies are a valuable method that can be used to assess such variability. In this study, we assess, in detail, intra-subject and inter-subject variability in a scenario based on a comprehensive dataset, including multiple repetitions of multi-directional reaching movements. The results show that muscle synergies are a valuable tool for quantifying variability at the muscle level and reveal that intra-subject variability is lower than inter-subject variability in synergy modules and related temporal coefficients, and both intra-subject and inter-subject similarity are higher than random synergy matching, confirming shared underlying control structures. The study deepens the available knowledge on muscle synergy-based motor function assessment and rehabilitation applications, discussing their applicability to real scenarios.

Strategies that simplify the control of quadrupedal stance. II. Electromyographic activity

1988 ◽  
Vol 60 (1) ◽  
pp. 218-231 ◽  
Author(s):  
J. M. Macpherson
Keyword(s):  
Muscle Synergy ◽  
Muscle Synergies ◽  
Electromyographic Activity ◽  
Supporting Surface ◽  
Force Vector ◽  
Tuning Curves ◽  
Hindlimb Muscles ◽  
Vector Generation ◽  
High Level ◽  
Selection Of

1. This study tested the hypothesis that muscle synergies underlie the invariance in the direction of corrective forces observed following stance perturbations in the horizontal plane. Electromyographic activity was recorded from selected forelimb and hindlimb muscles of cats subjected to horizontal translations of the supporting surface in 16 different directions. The responses of muscles were quantified for each perturbation, and tuning curves were constructed that related the amplitude of muscle response to the direction of platform movement. 2. Muscle tuning curves tended to group into one of two regions, corresponding to the two directions of force vectors. A few muscles showed clearly different recruitment patterns. The same direction of correction force vector was produced by different patterns of muscle activity, and the particular EMG pattern depended on the direction of platform movement. Therefore a simple muscle synergy organization could not account for the invariance in force vector generation. 3. It is concluded that there is a hierarchy of control in the maintenance of stance in which the vector of force exerted against the ground is a high level, task-dependent controlled variable and the selection of muscles to activate in order to produce the vector is controlled at a lower level. It is proposed that muscles are controlled using a modified synergy strategy. In this scheme, a synergy is not simply a fixed group of muscles, constrained to act as a unit. Rather, muscles are organized as a task-dependent synergy that is tuned or modified as needed by the addition or subtraction of other muscles.

scholarly journals Muscle Synergies Reliability in the Power Clean Exercise

2020 ◽  
Vol 5 (4) ◽  
pp. 75
Author(s):  
Paulo D. G. Santos ◽  
João R. Vaz ◽  
Paulo F. Correia ◽  
Maria J. Valamatos ◽  
António P. Veloso ◽  
...  
Keyword(s):  
Nonnegative Matrix Factorization ◽  
Nonnegative Matrix ◽  
Human Movement ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Complex Task ◽  
Muscle Coordination ◽  
High Similarity ◽  
Strength Tests ◽  
Power Clean

Muscle synergy extraction has been utilized to investigate muscle coordination in human movement, namely in sports. The reliability of the method has been proposed, although it has not been assessed previously during a complex sportive task. Therefore, the aim of the study was to evaluate intra- and inter-day reliability of a strength training complex task, the power clean, assessing participants’ variability in the task across sets and days. Twelve unexperienced participants performed four sets of power cleans in two test days after strength tests, and muscle synergies were extracted from electromyography (EMG) data of 16 muscles. Three muscle synergies accounted for almost 90% of variance accounted for (VAF) across sets and days. Intra-day VAF, muscle synergy vectors, synergy activation coefficients and individual EMG profiles showed high similarity values. Inter-day muscle synergy vectors had moderate similarity, while the variables regarding temporal activation were still strongly related. The present findings revealed that the muscle synergies extracted during the power clean remained stable across sets and days in unexperienced participants. Thus, the mathematical procedure for the extraction of muscle synergies through nonnegative matrix factorization (NMF) may be considered a reliable method to study muscle coordination adaptations from muscle strength programs.

scholarly journals Sensorimotor feedback based on task-relevant error robustly predicts temporal recruitment and multidirectional tuning of muscle synergies

2013 ◽  
Vol 109 (1) ◽  
pp. 31-45 ◽  
Author(s):  
Seyed A. Safavynia ◽  
Lena H. Ting
Keyword(s):  
Sagittal Plane ◽  
Balance Control ◽  
Center Of Mass ◽  
The Body ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Muscle Coordination ◽  
Initial State ◽  
Sensorimotor Feedback ◽  
Task Level

We hypothesized that motor outputs are hierarchically organized such that descending temporal commands based on desired task-level goals flexibly recruit muscle synergies that specify the spatial patterns of muscle coordination that allow the task to be achieved. According to this hypothesis, it should be possible to predict the patterns of muscle synergy recruitment based on task-level goals. We demonstrated that the temporal recruitment of muscle synergies during standing balance control was robustly predicted across multiple perturbation directions based on delayed sensorimotor feedback of center of mass (CoM) kinematics (displacement, velocity, and acceleration). The modulation of a muscle synergy's recruitment amplitude across perturbation directions was predicted by the projection of CoM kinematic variables along the preferred tuning direction(s), generating cosine tuning functions. Moreover, these findings were robust in biphasic perturbations that initially imposed a perturbation in the sagittal plane and then, before sagittal balance was recovered, perturbed the body in multiple directions. Therefore, biphasic perturbations caused the initial state of the CoM to differ from the desired state, and muscle synergy recruitment was predicted based on the error between the actual and desired upright state of the CoM. These results demonstrate that that temporal motor commands to muscle synergies reflect task-relevant error as opposed to sensory inflow. The proposed hierarchical framework may represent a common principle of motor control across motor tasks and levels of the nervous system, allowing motor intentions to be transformed into motor actions.

scholarly journals Motor Control System for Adaptation of Healthy Individuals and Recovery of Poststroke Patients: A Case Study on Muscle Synergies

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Fady S. Alnajjar ◽  
Juan C. Moreno ◽  
Ken-ichi Ozaki ◽  
Izumi Kondo ◽  
Shingo Shimoda
Keyword(s):  
Motor Control ◽  
Control System ◽  
Motor Recovery ◽  
Muscle Synergy ◽  
Behavioral Adaptation ◽  
Muscle Synergies ◽  
Healthy Individuals ◽  
Familiar Environment ◽  
Motor Control System ◽  
Healthy Participants

Understanding the complex neuromuscular strategies underlying behavioral adaptation in healthy individuals and motor recovery after brain damage is essential for gaining fundamental knowledge on the motor control system. Relying on the concept of muscle synergy, which indicates the number of coordinated muscles needed to accomplish specific movements, we investigated behavioral adaptation in nine healthy participants who were introduced to a familiar environment and unfamiliar environment. We then compared the resulting computed muscle synergies with those observed in 10 moderate-stroke survivors throughout an 11-week motor recovery period. Our results revealed that computed muscle synergy characteristics changed after healthy participants were introduced to the unfamiliar environment, compared with those initially observed in the familiar environment, and exhibited an increased neural response to unpredictable inputs. The altered neural activities dramatically adjusted through behavior training to suit the unfamiliar environment requirements. Interestingly, we observed similar neuromuscular behaviors in patients with moderate stroke during the follow-up period of their motor recovery. This similarity suggests that the underlying neuromuscular strategies for adapting to an unfamiliar environment are comparable to those used for the recovery of motor function after stroke. Both mechanisms can be considered as a recall of neural pathways derived from preexisting muscle synergies, already encoded by the brain’s internal model. Our results provide further insight on the fundamental principles of motor control and thus can guide the future development of poststroke therapies.

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.

scholarly journals The effect of arm weight support on upper limb muscle synergies during reaching movements

2014 ◽  
Vol 11 (1) ◽  
pp. 22 ◽  
Author(s):  
Martina Coscia ◽  
Vincent CK Cheung ◽  
Peppino Tropea ◽  
Alexander Koenig ◽  
Vito Monaco ◽  
...  
Keyword(s):  
Upper Limb ◽  
Reaching Movements ◽  
Muscle Synergies ◽  
Limb Muscle ◽  
Weight Support ◽  
Arm Weight Support

Muscle synergy extraction during arm reaching movements at different speeds

2017 ◽  
Vol 25 (1) ◽  
pp. 123-136 ◽  
Author(s):  
Vahid Reza Sabzevari ◽  
Amir Homayoun Jafari ◽  
Reza Boostani
Keyword(s):  
Muscle Synergy ◽  
Reaching Movements ◽  
Arm Reaching

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.

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