scholarly journals Fuzziness of muscle synergies in patients with multiple sclerosis indicates increased robustness of motor control during walking

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Lars Janshen ◽  
Alessandro Santuz ◽  
Antonis Ekizos ◽  
Adamantios Arampatzis
Keyword(s):  
Multiple Sclerosis ◽  
Motor Control ◽  
Muscle Synergies

scholarly journals Muscle Synergies in Patients With Multiple Sclerosis Reveal Demand-Specific Alterations in the Modular Organization of Locomotion

2021 ◽  
Vol 14 ◽  
Author(s):  
Lars Janshen ◽  
Alessandro Santuz ◽  
Adamantios Arampatzis
Keyword(s):  
Multiple Sclerosis ◽  
Motor Control ◽  
Motor Task ◽  
Time Dependent ◽  
Motor Deficits ◽  
Modular Organization ◽  
Muscle Synergies ◽  
Motor Primitives ◽  
Leg Muscles ◽  
Gait Parameters

For patients with multiple sclerosis (MS), deficits in gait significantly reduce the quality of life. Using the concept of muscle synergies, this study investigated the modular organization of motor control during level and inclined walking in MS patients (MSP) compared with healthy participants (HP) to identify the potential demand-specific adjustments in motor control in MSP. We hypothesized a widening of the time-dependent activation patterns (motor primitives) in MSP to increase the overlap of temporally-adjacent muscle synergies, especially during inclined walking, as a strategy to increase the robustness of motor control, thus compensating pathology-related deficits. We analyzed temporal gait parameters and muscle synergies from myoelectric signals of 13 ipsilateral leg muscles using non-negative matrix factorization. Compared with HP, MSP demonstrated a widening in the time-dependent coefficients (motor primitives), as well as altered relative muscle contribution (motor modules), in certain synergies during level and inclined walking. Moreover, inclined walking revealed a demand-specific adjustment in the modular organization in MSP, resulting in an extra synergy compared with HP. This further increased the overlap of temporally-adjacent muscle synergies to provide sufficient robustness in motor control to accomplish the more demanding motor task while coping with pathology-related motor deficits during walking.

Cerebellar Dysfunction in Multiple Sclerosis: Considerations for Research and Rehabilitation Therapy

2021 ◽  
pp. 154596832110654
Author(s):  
Erin M. Edwards ◽  
Nora E. Fritz ◽  
Amanda S. Therrien
Keyword(s):  
Multiple Sclerosis ◽  
Motor Control ◽  
Motor Impairment ◽  
Future Research ◽  
Disability Progression ◽  
Cerebellar Dysfunction ◽  
Motor Disability ◽  
Rehabilitation Outcomes ◽  
Critical Knowledge ◽  
The Impact

Introduction. Cerebellar pathology is common among persons with multiple sclerosis (PwMS). The cerebellum is well recognized for its role in motor control and motor learning and cerebellar pathology in multiple sclerosis is associated with enhanced motor impairment and disability progression. The Problem. To mitigate motor disability progression, PwMS are commonly prescribed exercise and task-specific rehabilitation training. Yet, whether cerebellar dysfunction differentially affects rehabilitation outcomes in this population remains unknown. Furthermore, we lack rehabilitation interventions targeting cerebellar dysfunction. The Solution. Here, we summarize the current understanding of the impact of cerebellar dysfunction on motor control, motor training, and rehabilitation in persons with multiple sclerosis. Recommendations. Additionally, we highlight critical knowledge gaps and propose that these guide future research studying cerebellar dysfunction in persons with multiple sclerosis.

Effect of gravity and kinematic constraints on muscle synergies in arm cycling.

2021 ◽  
Author(s):  
Lilla Botzheim ◽  
Jozsef Laczko ◽  
Diego Torricelli ◽  
Mariann Mravcsik ◽  
José L. Pons ◽  
...  
Keyword(s):  
Motor Control ◽  
Muscle Activation ◽  
Biceps Brachii ◽  
Body Position ◽  
Medical Rehabilitation ◽  
Muscle Synergies ◽  
Muscle Coordination ◽  
Arm Cycling ◽  
Custom Made ◽  
Crank Length

Arm cycling is a bi-manual motor task used in medical rehabilitation and in sports training. Understanding how muscle coordination changes across different biomechanical constraints in arm cycling is a step towards improved rehabilitation approaches. This exploratory study aims to get new insights on motor control during arm cycling. To achieve our main goal, we used the muscle synergies analysis to test three hypotheses: 1) body position with respect to gravity (sitting and supine) has an effect on muscle synergies; 2) the movement size (crank length) has an effect on the synergistic behavior; 3) the bimanual cranking mode (asynchronous and synchronous) requires different synergistic control. Thirteen able-bodied volunteers performed arm cranking on a custom-made device with unconnected cranks, which allowed testing three different conditions: body position (sitting versus supine), crank length (10cm versus 15cm) and cranking mode (synchronous versus asynchronous). For each of the eight possible combinations, subjects cycled for 30 seconds while electromyography of 8 muscles (4 from each arm) were recorded: biceps brachii, triceps brachii, anterior deltoid and posterior deltoid. Muscle synergies in this 8-dimensional muscle space were extracted by non-negative matrix factorization. Four synergies accounted for over 90% of muscle activation variances in all conditions. Results showed that synergies were affected by body position and cranking mode but practically unaffected by movement size. These results suggest that the central nervous system may employ different motor control strategies in response to external constraints such as cranking mode and body position during arm cycling.

scholarly journals Output Units of Motor Behavior: An Experimental and Modeling Study

2000 ◽  
Vol 12 (1) ◽  
pp. 78-97 ◽  
Author(s):  
E. P. Loeb ◽  
S. F. Giszter ◽  
P. Saltiel and E. Bizzi ◽  
F. A. Mussa-Ivaldi
Keyword(s):  
Motor Control ◽  
Common Property ◽  
Motor Behavior ◽  
Muscle Synergies ◽  
Force Output ◽  
Time Dynamics ◽  
Motor Behaviors ◽  
Distinct Property ◽  
Small Set ◽  
The Brain

Cognitive approaches to motor control typically concern sequences of discrete actions without taking into account the stunning complexity of the geometry and dynamics of the muscles. This begs the question: Does the brain convert the intricate, continuous-time dynamics of the muscles into simpler discrete units of actions, and if so, how? One way for the brain to form discrete units of behavior from muscles is through the synergistic co-activation of muscles. While this possibility has long been known, the composition of potential muscle synergies has remained elusive. In this paper, we have focused on a method that allowed us to examine and compare the limb stabilization properties of all possible muscle combinations. We found that a small set (as few as 23 out of 65,536) of all possible combinations of 16 limb muscles are robust with respect to activation noise: these muscle combinations could stabilize the limb at predictable, restricted portions of the workspace in spite of broad variations in the force output of their component muscles. The locations at which the robust synergies stabilize the limb are not uniformly distributed throughout the leg's workspace, but rather, they cluster at four workspace areas. The simulated robust synergies are similar to the actual synergies we have previously found to be generated by activation of the spinal cord. Thus, we have developed a new analytical method that enabled us to select a few muscle synergies with interesting properties out of the set of possible muscle combinations. Beyond this, the identification of robustness as a common property of the synergies in simple motor behaviors will open the way to the study of dynamic stability, which is an important and distinct property of the vertebrate motor-control system.

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 Deficits in tongue motor control are linked to microstructural brain damage in multiple sclerosis: a pilot study

BMC Neurology ◽  
2015 ◽  
Vol 15 (1) ◽  
Author(s):  
Florian Holtbernd ◽  
Michael Deppe ◽  
Rainald Bachmann ◽  
Siawoosh Mohammadi ◽  
Erich B. Ringelstein ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Motor Control ◽  
Pilot Study ◽  
Brain Damage

scholarly journals Sex-specific tuning of modular muscle activation patterns for locomotion in young and older adults

2021 ◽  
Author(s):  
Alessandro Santuz ◽  
Lars Janshen ◽  
Leon Bruell ◽  
Victor Munoz-Martel ◽  
Juri Taborri ◽  
...  
Keyword(s):  
Older Adults ◽  
Motor Control ◽  
Muscle Activation ◽  
Human Locomotion ◽  
Older Age ◽  
Modular Organization ◽  
Muscle Synergies ◽  
Activation Patterns ◽  
Motor Primitives ◽  
Muscle Activation Patterns

There is increasing evidence that including sex as a biological variable is of crucial importance to promote rigorous, repeatable and reproducible science. In spite of this, the body of literature that accounts for the sex of participants in human locomotion studies is small and often produces controversial results. Here, we investigated the modular organization of muscle activation patterns for human locomotion using the concept of muscle synergies with a double purpose: i) uncover possible sex-specific characteristics of motor control and ii) assess whether these are maintained in older age. We recorded electromyographic activities from 13 ipsilateral muscles of the lower limb in young and older adults of both sexes walking (young and old) and running (young) on a treadmill. The data set obtained from the 215 participants was elaborated through non-negative matrix factorization to extract the time-independent (i.e., motor modules) and time-dependent (i.e., motor primitives) coefficients of muscle synergies. We found sparse sex-specific modulations of motor control. Motor modules showed a different contribution of hip extensors, knee extensors and foot dorsiflexors in various synergies. Motor primitives were wider (i.e., lasted longer) in males in the propulsion synergy for walking (but only in young and not in older adults) and in the weight acceptance synergy for running. Moreover, the complexity of motor primitives was similar in younger adults of both sexes, but lower in older females as compared to older males. In essence, our results revealed the existence of small but defined sex-specific differences in the way humans control locomotion and that these strategies are not entirely maintained in older age.

scholarly journals The Dynamic Motor Control Index as a Marker of Age-Related Neuromuscular Impairment

2021 ◽  
Vol 13 ◽  
Author(s):  
Ashley N. Collimore ◽  
Ashlyn J. Aiello ◽  
Ryan T. Pohlig ◽  
Louis N. Awad
Keyword(s):  
Motor Control ◽  
Age Groups ◽  
Neuromuscular Control ◽  
Muscle Synergies ◽  
Age Related ◽  
Index Study ◽  
Two Measures ◽  
Study Participants ◽  
Young Old ◽  
Neuromuscular Impairment

Biomarkers that can identify age-related decline in walking function have potential to promote healthier aging by triggering timely interventions that can mitigate or reverse impairments. Recent evidence suggests that changes in neuromuscular control precede changes in walking function; however, it is unclear which measures are best suited for identifying age-related changes. In this study, non-negative matrix factorization of electromyography data collected during treadmill walking was used to calculate two measures of the complexity of muscle co-activations during walking for 36 adults: (1) the number of muscle synergies and (2) the dynamic motor control index. Study participants were grouped into young (18–35 years old), young-old (65–74 years old), and old–old (75+ years old) subsets. We found that the dynamic motor control index [χ2(2) = 9.41, p = 0.009], and not the number of muscle synergies [χ2(2) = 5.42, p = 0.067], differentiates between age groups [χ2(4) = 10.62, p = 0.031, Nagelkerke R2 = 0.297]. Moreover, an impairment threshold set at a dynamic motor control index of 90 (i.e., one standard deviation below the young adults) was able to differentiate between age groups [χ2(2) = 9.351, p = 0.009]. The dynamic motor control index identifies age-related differences in neuromuscular complexity not measured by the number of muscle synergies and may have clinical utility as a marker of neuromotor impairment.

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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