A Comprehensive Spatial Mapping of Muscle Synergies in Highly Variable Upper-Limb Movements of Healthy Subjects

Scano, Alessandro; Dardari, Luca; Molteni, Franco; Giberti, Hermes; Tosatti, Lorenzo Molinari; d’Avella, Andrea

doi:10.3389/fphys.2019.01231

Cited by 66 publications

(122 citation statements)

References 53 publications

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“…These challenges have only been partially addressed in literature. The effect of some of these sources of variability on extracted muscle synergies was already emphasized in several studies on healthy people, when assessing upper-limb intra-and inter-subject synergy composition similarity [5,21,22] or gait variability [23]. Several studies tried to quantify variability in various conditions, even in hardly comparable designs and topics.…”

Section: Introductionmentioning

confidence: 99%

“…These studies conclude that, in general, variability is found intra-session and intra-subject as well as inter-subject. However, much can be done to assess these sources of variability in more detail [5,20,22]. In the case of patient evaluations, it is expected that this variability is found as well and is even more prominent, since in general, neurological patient movements have a lower repeatability and larger heterogeneity at the kinematic and EMG level than those of healthy people [26,27].…”

Section: Introductionmentioning

confidence: 99%

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Variability of Muscle Synergies in Hand Grasps: Analysis of Intra- and Inter-Session Data

Pale

Atzori

Müller

et al. 2020

Sensors

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Background. Muscle synergy analysis is an approach to understand the neurophysiological mechanisms behind the hypothesized ability of the Central Nervous System (CNS) to reduce the dimensionality of muscle control. The muscle synergy approach is also used to evaluate motor recovery and the evolution of the patients’ motor performance both in single-session and longitudinal studies. Synergy-based assessments are subject to various sources of variability: natural trial-by-trial variability of performed movements, intrinsic characteristics of subjects that change over time (e.g., recovery, adaptation, exercise, etc.), as well as experimental factors such as different electrode positioning. These sources of variability need to be quantified in order to resolve challenges for the application of muscle synergies in clinical environments. The objective of this study is to analyze the stability and similarity of extracted muscle synergies under the effect of factors that may induce variability, including inter- and intra-session variability within subjects and inter-subject variability differentiation. The analysis was performed using the comprehensive, publicly available hand grasp NinaPro Database, featuring surface electromyography (EMG) measures from two EMG electrode bracelets. Methods. Intra-session, inter-session, and inter-subject synergy stability was analyzed using the following measures: variance accounted for (VAF) and number of synergies (NoS) as measures of reconstruction stability quality and cosine similarity for comparison of spatial composition of extracted synergies. Moreover, an approach based on virtual electrode repositioning was applied to shed light on the influence of electrode position on inter-session synergy similarity. Results. Inter-session synergy similarity was significantly lower with respect to intra-session similarity, both considering coefficient of variation of VAF (approximately 0.2–15% for inter vs. approximately 0.1% to 2.5% for intra, depending on NoS) and coefficient of variation of NoS (approximately 6.5–14.5% for inter vs. approximately 3–3.5% for intra, depending on VAF) as well as synergy similarity (approximately 74–77% for inter vs. approximately 88–94% for intra, depending on the selected VAF). Virtual electrode repositioning revealed that a slightly different electrode position can lower similarity of synergies from the same session and can increase similarity between sessions. Finally, the similarity of inter-subject synergies has no significant difference from the similarity of inter-session synergies (both on average approximately 84–90% depending on selected VAF). Conclusion. Synergy similarity was lower in inter-session conditions with respect to intra-session. This finding should be considered when interpreting results from multi-session assessments. Lastly, electrode positioning might play an important role in the lower similarity of synergies over different sessions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Variability of Muscle Synergies in Hand Grasps: Analysis of Intra- and Inter-Session Data

Pale

Atzori

Müller

et al. 2020

Sensors

Self Cite

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“…Several studies have investigated shared or merged muscle synergies across different tasks such as walking and running 8,42 , walking and cycling 25 , various directions of reaching 14,32 and stepping and non-stepping postural controls 35 . Their results indicated that different human behaviors use the fundamental motor modules that reflect the functional control units as a neural constraint on motor outputs.…”

Section: Discussionmentioning

confidence: 99%

Flexible recruitments of fundamental muscle synergies in the trunk and lower limbs for highly variable movements and postures

Saito

Yokoyama

Sasaki

et al. 2021

Preprint

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The extent to which muscle synergies represent the neural control of human behavior remains unknown. Here, we tested whether certain sets of muscle synergies that are fundamentally necessary across behaviors exist. We measured the electromyographic activities of 26 muscles including bilateral trunk and lower limb muscles during 24 locomotion, dynamic and static stability tasks, and extracted the muscle synergies using non-negative matrix factorization. Our results showed that 13 muscle synergies that may have unique functional roles accounted for almost all 24 tasks by combinations of single and/or merging of synergies. Therefore, our results may support the notion of the low dimensionality in motor outputs, in which the central nervous system flexibly recruits fundamental muscle synergies to execute diverse human behaviors. Further studies using manipulations of the central nervous system and/or neural recording are required the neural representation with such fundamental components of muscle synergies.

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“…This finding seems to point at a more flexible character of the linking of DOF in synergies, which is in line with several papers demonstrating that muscle synergies differed across task constraints cf. 39,53,54,59–63 . An alternative perspective suggests that the large base of movements can generally characterised as the combination of dynamic primitives 64 .…”

Section: Discussionmentioning

confidence: 99%

Synergies reciprocally relate end-effector and joint-angles in rhythmic pointing movements

Valk

Mouton

Otten

et al. 2019

Sci Rep

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During rhythmic pointing movements, degrees of freedom (DOF) in the human action system—such as joint-angles in the arm—are assumed to covary to stabilise end-effector movement, e.g. index finger. In this paper, it is suggested that the end-effector movement and the coordination of DOF are reciprocally related in synergies that link DOF so as to produce the end-effector movement. The coordination of DOF in synergies and the relation between end-effector movement and DOF coordination received little attention, though essential to understand the principles of synergy formation. Therefore, the current study assessed how the end-effector movement related to the coordination of joint-angles during rhythmic pointing across target widths and distances. Results demonstrated that joint-angles were linked in different synergies when end-effector movements differed across conditions. Furthermore, in every condition, three joint-angles (shoulder plane of elevation, shoulder inward-outward rotation, elbow flexion-extension) largely drove the end-effector, and all joint-angles contributed to covariation that stabilised the end-effector. Together, results demonstrated synergies that produced the end-effector movement, constrained joint-angles so that they covaried to stabilise the end-effector, and differed when end-effector movement differed. Hence, end-effector and joint-angles were reciprocally related in synergies—indicating that the action system was organised as a complex dynamical system.

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A Comprehensive Spatial Mapping of Muscle Synergies in Highly Variable Upper-Limb Movements of Healthy Subjects

Cited by 66 publications

References 53 publications

Variability of Muscle Synergies in Hand Grasps: Analysis of Intra- and Inter-Session Data

Variability of Muscle Synergies in Hand Grasps: Analysis of Intra- and Inter-Session Data

Flexible recruitments of fundamental muscle synergies in the trunk and lower limbs for highly variable movements and postures

Synergies reciprocally relate end-effector and joint-angles in rhythmic pointing movements

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