Phasic and tonic muscle synergies are different in number, structure and sparseness

Effect of Eccentric Training with Different Durations, Intensities, and Contraction Velocities on Upper Limb Muscle Strength: A Meta-Analysis

Eccentric training may be more effective for muscle strength, but the optimal duration, intensity, and contraction velocity for improving upper limb strength remain unclear. We conducted a search across four databases (PubMed, Embase, Web of Science, and Cochrane) to evaluate the impact of eccentric training on upper limb skeletal muscle strength. A meta-analysis using standardized mean differences (SMDs) and 95% confidence intervals (CIs) was performed. The results from 11 studies involving 368 participants indicated that eccentric training significantly enhanced upper limb strength (SMD = 0.55, CI: 0.32-0.79). Subgroup analysis showed a slight increase in strength in the 1-4 week period (SMD = 0.38, CI: 0.02-0.73), a significant increase in the 4-8 week period (SMD = 0.69, CI: 0.27-1.10), and a substantial increase at 20 weeks (SMD = 0.71, CI: 0.22-1.21). Moderate intensity showed moderate improvements (SMD = 0.47, CI: 0.18-0.77), while high intensity led to significant adaptations (SMD = 0.70, CI: 0.30-1.10). Rapid eccentric contractions (SMD = 0.70, CI: 0.39-1.02) outperformed slow contractions (SMD = 0.35, CI: -0.01-0.71). Eccentric training is effective, with significant results generally requiring 4-8 weeks of high-intensity rapid eccentric training.

Spinal maps in phasic and tonic EMG: Investigating intra-subject and inter-subject variability

Reaching movements are essential for daily tasks and they have been widely investigated through kinematic, kinetic, and electromyographic (EMG) analyses. Recent studies have suggested that the central nervous system simplifies control of reaching movements by using muscle synergies. An alternative approach is to investigate how EMG activity reflects at theneural level with the representation of spinal maps that visualize the spatiotemporal activity of motoneuronal pools. Spinal maps have been rarely used and their investigation could be made by exploiting recent findings in EMG processing such as the separation of phasic (motion-related) and tonic components (anti-gravity). In this study, we aimed at characterizing spinal maps in the upper limb workspace. EMG data from 15 participants were recorded during repeated point-to-point movements toward target boards placed in five orientations. EMG waveforms were divided into total EMG envelope, tonic EMG, and phasic EMG. The multidimensional Pearson's correlation coefficient was used to assess thesimilarity of spinal maps among repetitions of movements within subjects (intra-subject variability) and among participants (inter-subject variability). Spinal maps of tonic and total EMG showed high intra- and inter-subject similarity in all planes, while phasic spinal maps were less repeatable and more subject-specific. These results may be useful as areference for rehabilitation, clinical, and neurological evaluations, especially for longitudinal assessments.

A methodological scoping review on EMG processing and synergy-based results in muscle synergy studies in Parkinson's disease

Introduction

Parkinson's Disease is the second most common neurodegenerative disease in the world. It affects mainly people over 65 and the incidence increases with age. It is characterized by motor and non-motor symptoms and several clinical manifestations. The most evident symptom that affects all patients with Parkinson's Disease is the impairment of motor control, including bradykinesia, tremor, joint rigidity, and postural instability. In the literature, it has been evaluated with muscle synergies, a well-known method for evaluating motor control at the muscular level. However, few studies are available and there is still a major gap to fill to exploit the potential of the method for assessing motor control in Parkinson's Disease, both in the understanding of physiopathology and clinical practice.

Methods

In the light of understanding and fostering future developments for the field, in this review we initially screened 212 papers on Scopus and Web of Science and selected 15 of them to summarize the main features of investigations that employed muscle synergies to analyze patients with Parkinson's Disease. We detailed the features of the screened papers by reporting the clinical findings, a detailed report of EMG processing choices and synergy-based results.

Results

We found that synergistic control is in general altered in patients with Parkinson's Disease, but it can improve if patients are subjected to pharmacological and rehabilitation therapies. Moreover, a further understanding of synergistic control in Parkinson's patients is needed.

Discussion

We discuss the future developments in the field with a detailed assessment of the topic on the view of physicians, including the most promising lines of research for clinical practice and from the perspective of engineers, for methodological application of synergistic approaches.

SynergyAnalyzer: A Matlab toolbox implementing mixed-matrix factorization to identify kinematic-muscular synergies

BACKGROUND AND OBJECTIVE

A new direction in the study of motor control was opened about two decades ago with the introduction of a model for the generation of motor commands as combination of muscle synergies. Muscle synergies provide a simple yet quantitative framework for analyzing the hierarchical and modular architecture of the human motor system. However, to gain insights on the functional role of muscle synergies, they should be related to the task space. The recently introduced mixed-matrix factorization (MMF) algorithm extends the standard approach for synergy extraction based on non-negative matrix factorization (NMF) allowing to factorize data constituted by a mixture of non-negative variables (e.g. EMGs) and unconstrained variables (e.g. kinematics, naturally including both positive and negative values). The kinematic-muscular synergies identified by MMF provide a direct link between muscle synergies and the task space. In this contribution, we support the adoption of MMF through a Matlab toolbox for the extraction of kinematic-muscular synergies and a set of practical guidelines to allow biomedical researchers and clinicians to exploit the potential of this novel approach.

METHODS

MMF is implemented in the SynergyAnalyzer toolbox using an object-oriented approach. In addition to the MMF algorithm, the toolbox includes standard methods for synergy extraction (NMF and PCA), as well as methods for pre-processing EMG and kinematic data, and for plotting data and synergies.

RESULTS

As an example of MMF application, kinematic-muscular synergies were extracted from EMG and kinematic data collected during reaching movements towards 8 targets on the sagittal plane. Instructions and command lines to achieve such results are illustrated in detail. The toolbox has been released as an open-source software on GitHub under the GNU General Public License.

CONCLUSIONS

Thanks to its ease of use and adaptability to a variety of datasets, SynergyAnalyzer will facilitate the adoption of MMF to extract kinematic-muscular synergies from mixed EMG and kinematic data, a useful approach in biomedical research to better understand and characterize the functional role of muscle synergies.

Human arm redundancy: a new approach for the inverse kinematics problem

The inverse kinematics (IK) problem addresses how both humans and robotic systems coordinate movement to resolve redundancy, as in the case of arm reaching where more degrees of freedom are available at the joint versus hand level. This work focuses on which coordinate frames best represent human movements, enabling the motor system to solve the IK problem in the presence of kinematic redundancies. We used a multi-dimensional sparse source separation method to derive sets of basis (or source) functions for both the task and joint spaces, with joint space represented by either absolute or anatomical joint angles. We assessed the similarities between joint and task sources in each of these joint representations, finding that the time-dependent profiles of the absolute reference frame's sources show greater similarity to corresponding sources in the task space. This result was found to be statistically significant. Our analysis suggests that the nervous system represents multi-joint arm movements using a limited number of basis functions, allowing for simple transformations between task and joint spaces. Additionally, joint space seems to be represented in an absolute reference frame to simplify the IK transformations, given redundancies. Further studies will assess this finding's generalizability and implications for neural control of movement.

Isometric vs Isotonic Core Stabilization Exercises to Improve Pain and Disability in Patients with Non-specific Chronic Low Back Pain: A Randomized Controlled Trial

Background

Non-specific chronic low back pain (NSCLBP) is a prevalent condition that affects 90% of individuals experiencing low back pain. Core stabilization exercises (CSE) stand out as the most commonly employed therapeutic approach for managing NSCLBP. Nevertheless, there remains uncertainty regarding the superior effectiveness between isometric (ISOM) and isotonic (ISOT) types of CSE in the treatment of NSCLBP.

Objectives

The primary objective of this study was to compare the efficacy of ISOM and ISOT exercises concerning pain and disability in patients with NSCLBP. Additionally, the study aimed to assess the effectiveness of both ISOM and ISOT in comparison to no intervention concerning these variables in these patients.

Methods

This study was a randomized controlled trial that involved 41 men and women experiencing NSCLBP. Participants were randomly allocated to three groups: ISOM CSE (n = 13), ISOT CSE (n = 14), and a waitlist control (n = 14). The exercise training was administered for 40 - 60 minutes three times a week over a period of up to 8 weeks. Pain (assessed using the Visual Analog Scale or VAS) and disability (evaluated through the Oswestry Disability Index or ODI) variables were measured before and after the interventions.

Results

Based on the results, there was no significant difference between the 2 exercise groups (ISOM and ISOT) regarding pain and disability. However, the ISOM group demonstrated numerically better results than the ISOT group. Both the ISOM and ISOT groups exhibited a significant decrease in pain levels, with the VAS score decreasing from 5.5 to 2.7 for ISOM and from 5.8 to 3.7 for ISOT, as compared to the control group (P < 0.001 and P = 0.001, respectively). Additionally, the average disability showed a significant improvement in both the ISOM (ODI score from 17 to 11) and ISOT (ODI score from 15.4 to 11) groups compared to the control group (P < 0.001).

Conclusions

Both ISOM and ISOT methods are effective in alleviating pain and disability in patients with NSCLBP. However, there is no significant difference in the benefits between them. Numerically, ISOM exercises were found to be superior. Further studies are needed to obtain a more accurate answer regarding their superiority.