Challenges and New Approaches to Proving the Existence of Muscle Synergies of Neural Origin

Muscle coordination studies repeatedly show low-dimensionality of muscle activations for a wide variety of motor tasks. The basis vectors of this low-dimensional subspace, termed muscle synergies, are hypothesized to reflect neurally-established functional muscle groupings that simplify body control. However, the muscle synergy hypothesis has been notoriously difficult to prove or falsify. We use cadaveric experiments and computational models to perform a crucial thought experiment and develop an alternative explanation of how muscle synergies could be observed without the nervous system having controlled muscles in groups. We first show that the biomechanics of the limb constrains musculotendon length changes to a low-dimensional subspace across all possible movement directions. We then show that a modest assumption—that each muscle is independently instructed to resist length change—leads to the result that electromyographic (EMG) synergies will arise without the need to conclude that they are a product of neural coupling among muscles. Finally, we show that there are dimensionality-reducing constraints in the isometric production of force in a variety of directions, but that these constraints are more easily controlled for, suggesting new experimental directions. These counter-examples to current thinking clearly show how experimenters could adequately control for the constraints described here when designing experiments to test for muscle synergies—but, to the best of our knowledge, this has not yet been done

Modulating the structure of motor variability for skill learning through specific muscle synergies in elderlies and young adults

202111 bchyVersion of RecordPublishe

Plasticity of muscle synergies through fractionation and merging during development and training of human runners

202012 bcrcVersion of RecordPublishe

Decomposing Time Series Data by a Non-negative Matrix Factorization Algorithm with Temporally Constrained Coefficients

The non-negative matrix factorization algorithm (NMF) decomposes a data matrix into a set of non-negative basis vectors, each scaled by a coefficient. In its original formulation, the NMF assumes the data samples and dimensions to be independently distributed, making it a lessthan-ideal algorithm for the analysis of time series data with temporal correlations. Here, we seek to derive an NMF that accounts for temporal dependencies in the data by explicitly incorporating a very simple temporal constraint for the coefficients into the NMF update rules. We applied the modified algorithm to 2 multi-dimensional electromyographic data sets collected from the human upper-limb to identify muscle synergies. We found that because it reduced the number of free parameters in the model, our modified NMF made it possible to use the Akaike Information Criterion to objectively identify a model order (i.e., the number of muscle synergies composing the data) that is more functionally interpretable, and closer to the numbers previously determined using ad hoc measures

Adapting to the mechanical properties and active force of an exoskeleton by altering muscle synergies in chronic stroke survivors

Title on author’s file: Normalization of lower-limb muscle synergies during gait training with a powered ankle exoskeleton in chronic stroke survivors202103 bcvcAccepted ManuscriptSelf-fundedPublishe

Acupuncture and related interventions for carpal tunnel syndrome: systematic review

© The Author(s) 2019. Objective: To synthesize evidence on the effectiveness of acupuncture and related therapies for primary carpal tunnel syndrome (CTS) by conducting a systematic review of randomized controlled trials (RCTs). Data Sources: Nine databases were searched for potential RCTs from their inception till July 2019. Review Methods: RCTs which reported at least one of the three outcomes were included: symptom severity, functional status and pain. Included RCTs were appraised using the Cochrane Risk of Bias Tool. Results: A total of 10 RCTs (728 participants) were included. Majority were at high risk of bias for blinding of participants, personnel and outcome assessors. When compared to conventional medications, manual acupuncture showed significant superior effect in reducing symptom than ibuprofen (mean difference (MD) on Symptom Severity Scale (SSS)) = –5.80, 95% confidence interval (CI): −7.95 to −3.65) and prednisolone (MD = −6.50, 95% CI: −10.1, −2.86). Electroacupuncture plus splinting was more effective in reducing symptom severity than splinting alone (SSS score: MD = −0.20, 95% CI: −0.36 to −0.03). Manual acupuncture showed significantly superior effect than ibuprofen in improving functional status (Functional Status Scale (FSS): MD = −1.84, 95% CI: −2.66 to −1.02). The combination of electroacupuncture and splinting showed more improvement in functional status compared to splinting alone (FSS: MD = −6.22, 95%CI: −10.7 to −1.71). Triple treatment of acupuncture, magnetic spectrum heat lamp and splinting showed stronger pain relief than splinting alone. Conclusion: For both symptom relief and function improvement, manual acupuncture is superior to ibuprofen while electroacupuncture plus splinting outperforms splinting alone. Limited evidence showed electroacupuncture’s potential role in pain reduction