2022
Design and validation of a wireless Body Sensor Network for integrated EEG and HD-sEMG acquisitions
doi: 10.1109/TNSRE.2022.3140220. Epub 2022 Jan 28.
Design and Validation of a Wireless Body Sensor Network for Integrated EEG and HD-sEMG Acquisitions
PMID: 34982687
Abstract
Sensorimotor integration is the process through which the human brain plans the motor program execution according to external sources. Within this context, corticomuscular and corticokinematic coherence analyses are common methods to investigate the mechanism underlying the central control of muscle activation. This requires the synchronous acquisition of several physiological signals, including EEG and sEMG. Nevertheless, physical constraints of the current, mostly wired, technologies limit their application in dynamic and naturalistic contexts. In fact, although many efforts were made in the development of biomedical instrumentation for EEG and High Density-surface EMG (HD-sEMG) signal acquisition, the need for an integrated wireless system is emerging. We hereby describe the design and validation of a new fully wireless body sensor network for the integrated acquisition of EEG and HD-sEMG signals. This Body Sensor Network is composed of wireless bio-signal acquisition modules, named sensor units, and a set of synchronization modules used as a general-purpose system for time-locked recordings. The system was characterized in terms of accuracy of the synchronization and quality of the collected signals. An in-depth characterization of the entire system and an head-to-head comparison of the wireless EEG sensor unit with a wired benchmark EEG device were performed. The proposed device represents an advancement of the State-of-the-Art technology allowing the integrated acquisition of EEG and HD-sEMG signals for the study of sensorimotor integration.
Changes in the distribution of muscle activity when using a passive trunk exoskeleton depend on the type of working task: A high-density surface EMG study
doi: 10.1016/j.jbiomech.2021.110846. Epub 2021 Oct 28.
Changes in the distribution of muscle activity when using a passive trunk exoskeleton depend on the type of working task: A high-density surface EMG study
Abstract
Exoskeleton effectiveness in reducing muscle efforts has been usually assessed from surface electromyograms (EMGs) collected locally. It has been demonstrated, however, muscle activity redistributes within the low back muscles during static and dynamic contractions, suggesting the need of detecting surface EMGs from a large muscle region to reliably investigate changes in global muscle activation. This study used high-density surface EMG to assess the effects of a passive trunk exoskeleton on the distribution of low back muscles’ activity during different working tasks. Ten, male volunteers performed a static and a dynamic task with and without the exoskeleton. Multiple EMGs were sampled bilaterally from the lumbar erector spinae muscles while the hip and knee angles were measured unilaterally. Key results revealed for the static task exoskeleton led to a decrease in the average root mean square (RMS) amplitude (∼10%) concomitantly with a stable mean frequency and a redistribution of muscle activity (∼0.5 cm) in the caudal direction toward the end of the task. For the dynamic task, the exoskeleton reduced the RMS amplitude (∼5%) at the beginning of the task and the variability in the muscle activity distribution during the task. Moreover, a reduced range of motion in the lower limb was observed when using the exoskeleton during the dynamic task. Current results support the notion the passive exoskeleton has the potential to alleviate muscular loading at low back level especially for the static task.
Keywords: Ergonomics; Exoskeleton; Surface electromyography.
Physical and electrophysiological motor unit characteristics are revealed with simultaneous high-density electromyography and ultrafast ultrasound imaging
doi: 10.1038/s41598-022-12999-4.
Physical and electrophysiological motor unit characteristics are revealed with simultaneous high-density electromyography and ultrafast ultrasound imaging
Abstract
Electromyography and ultrasonography provide complementary information about electrophysiological and physical (i.e. anatomical and mechanical) muscle properties. In this study, we propose a method to assess the electrical and physical properties of single motor units (MUs) by combining High-Density surface Electromyography (HDsEMG) and ultrafast ultrasonography (US). Individual MU firings extracted from HDsEMG were used to identify the corresponding region of muscle tissue displacement in US videos. The time evolution of the tissue velocity in the identified region was regarded as the MU tissue displacement velocity. The method was tested in simulated conditions and applied to experimental signals to study the local association between the amplitude distribution of single MU action potentials and the identified displacement area. We were able to identify the location of simulated MUs in the muscle cross-section within a 2 mm error and to reconstruct the simulated MU displacement velocity (cc > 0.85). Multiple regression analysis of 180 experimental MUs detected during isometric contractions of the biceps brachii revealed a significant association between the identified location of MU displacement areas and the centroid of the EMG amplitude distribution. The proposed approach has the potential to enable non-invasive assessment of the electrical, anatomical, and mechanical properties of single MUs in voluntary contractions.
Keywords: Ultrasound, HDsEMG, Motor units
2021
Design of a Programmable and Modular Neuromuscular Electrical Stimulator Integrated into a Wireless Body Sensor Network
2021
Design of a Programmable and Modular Neuromuscular Electrical Stimulator Integrated into a Wireless Body Sensor Network
DOI: 10.1109/ACCESS.2021.3133096
Abstract
Neuromuscular electrical stimulation finds application in several fields, from basic neurophysiology, to motor rehabilitation and cardiovascular conditioning. Despite the progressively increasing interest in this technique, its State-of-the-Art technology is mainly based on monolithic, mostly wired devices, leading to two main issues. First, these devices are often bulky, limiting their usability in applied contexts. Second, the possibility of interfacing these stimulation devices with external systems for the acquisition of electrophysiological and biomechanical variables to control the stimulation output is often limited. The aim of this work is to describe the design and development of an innovative electrical stimulator, specifically developed to contend with these issues. The developed device is composed of wireless modules that can be programmed and easily interfaced with third-party instrumentation. Moreover, benefiting from the system modular architecture, stimulation may be delivered concurrently to different sites while greatly reducing cable encumbrance. The main design choices and experimental tests are documented, evidencing the practical potential of the device in use-case scenarios.
INDEX TERMS Electrical stimulation, functional electrical stimulation, medical.
Orientation Estimation Through Magneto-Inertial Sensor Fusion: A Heuristic Approach for Suboptimal Parameters Tuning
2021
Orientation Estimation Through Magneto-Inertial Sensor Fusion: A Heuristic Approach for Suboptimal Parameters Tuning
DOI: 10.1109/ACCESS.2021.3133096
Abstract
Magneto-Inertial Measurement Units (MIMUs) are a valid alternative tool to optical stereophotogrammetry in human motion analysis. The orientation of a MIMU may be estimated by using sensor fusion algorithms. Such algorithms require input parameters that are usually set using a trial-and-error (or grid-search) approach to find the optimal values. However, using trial-and-error requires a known reference orientation, a circumstance rarely occurring in real-life applications. In this article, we present a way to suboptimally set input parameters, by exploiting the assumption that two MIMUs rigidly connected are expected to show no orientation difference during motion. This approach was validated by applying it to the popular complementary filter by Madgwick et al. and tested on 18 experimental conditions including three commercial products, three angular rates, and two dimensionality motion conditions. Two main findings were observed: i) the selection of the optimal parameter value strongly depends on the specific experimental conditions considered, ii) in 15 out of 18 conditions the errors obtained using the proposed approach and the trial-and-error were coincident, while in the other cases the maximum discrepancy amounted to 2.5 deg and less than 1.5 deg on average.
Dynamic Surface Electromyography Using Stretchable Screen-Printed Textile Electrodes
doi: 10.1109/TNSRE.2021.3104972. Epub 2021 Aug 27.
Dynamic Surface Electromyography Using Stretchable Screen-Printed Textile Electrodes
PMID: 34398755
Abstract
Objective: Wearable devices have created new opportunities in healthcare and sport sciences by unobtrusively monitoring physiological signals. Textile polymer-based electrodes proved to be effective in detecting electrophysiological potentials but suffer mechanical fragility and low stretch resistance. The goal of this research is to develop and validate in dynamic conditions cost-effective and easily manufacturable electrodes characterized by adequate robustness and signal quality.
Methods: We here propose an optimized screen printing technique for the fabrication of PEDOT:PSS-based textile electrodes directly into finished stretchable garments for surface electromyography (sEMG) applications. A sensorised stretchable leg sleeve was developed, targeting five muscles of interest in rehabilitation and sport science. An experimental validation was performed to assess the accuracy of signal detection during dynamic exercises, including sit-to-stand, leg extension, calf raise, walking, and cycling.
Results: The electrodes can resist up to 500 stretch cycles. Tests on five subjects revealed excellent contact impedance, and cross-correlation between sEMG envelopes simultaneously detected from the leg muscles by the textile and Ag/AgCl electrodes was generally greater than 0.9, which proves that it is possible to obtain good quality signals with performance comparable with disposable electrodes.
Conclusions: An effective technique to embed polymer-based electrodes in stretchable smart garments was presented, revealing good performance for dynamic sEMG detections.
Significance: The achieved results pave the way to the integration of unobtrusive electrodes, obtained by screen printing of conductive polymers, into technical fabrics for rehabilitation and sport monitoring, and in general where the detection of sEMG in dynamic conditions is necessary.
Long short-term memory (LSTM) recurrent neural network for muscle activity detection
2021 Oct 21;18(1):153.
doi: 10.1186/s12984-021-00945-w.
Long short-term memory (LSTM) recurrent neural network for muscle activity detection
PMID: 34674720
PMCID: PMC8532313
Abstract
Background: The accurate temporal analysis of muscle activation is of great interest in many research areas, spanning from neurorobotic systems to the assessment of altered locomotion patterns in orthopedic and neurological patients and the monitoring of their motor rehabilitation. The performance of the existing muscle activity detectors is strongly affected by both the SNR of the surface electromyography (sEMG) signals and the set of features used to detect the activation intervals. This work aims at introducing and validating a powerful approach to detect muscle activation intervals from sEMG signals, based on long short-term memory (LSTM) recurrent neural networks.
Methods: First, the applicability of the proposed LSTM-based muscle activity detector (LSTM-MAD) is studied through simulated sEMG signals, comparing the LSTM-MAD performance against other two widely used approaches, i.e., the standard approach based on Teager-Kaiser Energy Operator (TKEO) and the traditional approach, used in clinical gait analysis, based on a double-threshold statistical detector (Stat). Second, the effect of the Signal-to-Noise Ratio (SNR) on the performance of the LSTM-MAD is assessed considering simulated signals with nine different SNR values. Finally, the newly introduced approach is validated on real sEMG signals, acquired during both physiological and pathological gait. Electromyography recordings from a total of 20 subjects (8 healthy individuals, 6 orthopedic patients, and 6 neurological patients) were included in the analysis.
Results: The proposed algorithm overcomes the main limitations of the other tested approaches and it works directly on sEMG signals, without the need for background-noise and SNR estimation (as in Stat). Results demonstrate that LSTM-MAD outperforms the other approaches, revealing higher values of F1-score (F1-score > 0.91) and Jaccard similarity index (Jaccard > 0.85), and lower values of onset/offset bias (average absolute bias < 6 ms), both on simulated and real sEMG signals. Moreover, the advantages of using the LSTM-MAD algorithm are particularly evident for signals featuring a low to medium SNR.
Conclusions: The presented approach LSTM-MAD revealed excellent performances against TKEO and Stat. The validation carried out both on simulated and real signals, considering normal as well as pathological motor function during locomotion, demonstrated that it can be considered a powerful tool in the accurate and effective recognition/distinction of muscle activity from background noise in sEMG signals.
Keywords: Deep learning; EMG; EMG-based interfaces; Gait analysis; Muscle activation intervals; Muscle activity; Onset-offset detection; RNN; Surface electromyography.
Electrodes’ configuration influences the agreement between surface EMG and b-mode ultrasound detection of motor unit fasciculation
Open Access Volume 9, Pages 98110 – 981202021 Article number 9474475
Electrodes’ Configuration Influences the Agreement between Surface EMG and B-Mode Ultrasound Detection of Motor Unit Fasciculation
PMID: 32192073
PMCID: PMC7147320
DOI: 10.3390/s20061666
Abstract
Muscle fasciculations, resulting from the spontaneous activation of motor neurons, may be associated with neurological disorders, and are often assessed with intramuscular electromyography (EMG). Recently, however, both ultrasound (US) imaging and multichannel surface EMG have been shown to be more sensitive to fasciculations. In this study we combined these two techniques to compare their detection sensitivity to fasciculations occurring in different muscle regions and to investigate the effect of EMG electrodes‘ configuration on their agreement. Monopolar surface EMGs were collected from medial gastrocnemius and soleus with an array of 32 electrodes (10 mm Inter-Electrode Distance, IED) simultaneously with b-mode US images detected alongside either proximal, central or distal electrodes groups. Fasciculation potentials (FP) were identified from single differential EMGs with 10 mm (SD1), 20 mm (SD2) and 30 mm (SD3) IEDs, and fasciculation events (FE) from US image sequences. The number, location, and size of FEs and FPs in 10 healthy participants were analyzed. Overall, the two techniques showed similar sensitivities to muscle fasciculations. US was equally sensitive to FE occurring in the proximal and distal calf regions, while the number of FP revealed by EMG increased significantly with the IED and was larger distally, where the depth of FE decreased. The agreement between the two techniques was relatively low, with a percentage of fasciculation classified as common ranging from 22% for the smallest IED to 68% for the largest IED. The relevant number of events uniquely detected by the two techniques is discussed in terms of different spatial sensitivities of EMG and US, which suggest that a combination of US-EMG is likely to maximise the sensitivity to muscle fasciculations. © 2013 IEEE.
Author keywords
Changes in supramaximal M-wave amplitude at different regions of biceps brachii following eccentric exercise of the elbow flexors
doi: 10.1007/s00421-020-04520-4. Epub 2020 Oct 17.
Changes in supramaximal M-wave amplitude at different regions of biceps brachii following eccentric exercise of the elbow flexors
PMID: 33070208
Abstract
Purpose: Previous evidence from surface electromyograms (EMGs) suggests that exercise-induced muscle damage (EIMD) may manifest unevenly within the muscle. Here we investigated whether these regional changes were indeed associated with EIMD or if they were attributed to spurious factors often affecting EMGs.
Methods: Ten healthy male subjects performed 3 × 10 eccentric elbow flexions. Maximal voluntary contraction (MVC), muscle soreness and ultrasound images from biceps brachii distal and proximal regions were measured immediately before (baseline) and during each of the following 4 days after the exercise. Moreover, 64 monopolar surface EMGs were detected while 10 supramaximal pulses were applied to the musculocutaneous nerve. The innervation zone (IZ), the number of electrodes detecting largest M-waves and their centroid longitudinal coordinates were assessed to characterize the spatial distribution of the M-waves amplitude.
Results: The MVC torque decreased (~ 25%; P < 0.001) while the perceived muscle soreness scale increased (~ 4 cm; 0 cm for no soreness and 10 cm for highest imaginable soreness; P < 0.005) across days. The echo intensity of the ultrasound images increased at 48 h (71%), 72 h (95%) and 96 h (112%) for both muscle regions (P < 0.005), while no differences between regions were observed (P = 0.136). The IZ location did not change (P = 0.283). The number of channels detecting the greatest M-waves significantly decreased (up to 10.7%; P < 0.027) and the centroid longitudinal coordinate shifted distally at 24, 48 and 72 h after EIMD (P < 0.041).
Conclusion: EIMD consistently changed supramaximal M-waves that were detected mainly proximally from the biceps brachii, suggesting that EIMD takes place locally within the biceps brachii.
Keywords: Eccentric contractions; High-density surface electromyography; Muscle damage; Neuromuscular electrical stimulation.; Ultrasound echo intensity.
Understanding regional activation of thoraco-lumbar muscles in chronic low back pain and its relationship to clinically relevant domains
doi: 10.1186/s12891-021-04287-5.
Understanding regional activation of thoraco-lumbar muscles in chronic low back pain and its relationship to clinically relevant domains
PMID: 33975570
PMCID: PMC8114502
Abstract
Background: Altered regional activation of the lumbar extensors has been previously observed in individuals with low back pain (LBP) performing high-effort and fatiguing tasks. It is currently unknown whether similar alterations can be observed during low-effort functional tasks. Similarly, previous studies did not investigate whether side differences in regional activation are present in individuals with LBP. Finally, there is limited evidence of whether the extent of the alteration of regional activation is associated with clinical factors. Therefore, the aim of this study was to investigate whether individuals with LBP exhibit asymmetric regional activation of the thoraco-lumbar extensor muscles during functional tasks, and if the extent of neuromuscular control alteration is associated with clinical and psychosocial outcome domains.
Methods: 21 participants with and 21 without LBP performed five functional tasks (gait, sit-to-stand, forward trunk flexion, shoulder flexion and anterior pelvic tilt). The spatial distribution of activation of the thoraco-lumbar extensor muscles was assessed bilaterally using high-density electromyography. For each side, the distribution of electromyographic (EMG) amplitude was characterized in terms of intensity, location and size. Indices of asymmetry were calculated from these features and comparisons between groups and tasks were performed using ANOVA. The features that significantly differed between groups were correlated with self-reported measures of pain intensity and other outcome domains.
Results: Indices of asymmetry did not differ between participants with and without LBP (p > 0.11). The cranio-caudal location of the activation differed between tasks (p < 0.05), but not between groups (p = 0.64). Participants with LBP showed reduced EMG amplitude during anterior pelvic tilt and loading response phase during gait (both p < 0.05). Pearson correlation revealed that greater pain intensity was associated with lower EMG amplitude for both tasks (R<-0.5, p < 0.05).
Conclusions: Despite clear differences between tasks, individuals with and without LBP exhibited similar distributions of EMG amplitude during low-effort functional activities, both within and between sides. However, individuals with LBP demonstrated lower activation of the thoraco-lumbar muscles during gait and anterior pelvic tilt, especially those reporting higher pain intensity. These results have implications in the development or refinement of assessment and intervention strategies focusing on motor control in patients with chronic LBP.
Keywords: Low back pain; clinical outcomes; electromyography; neuromuscular adaptation.
Novel Insights Into Biarticular Muscle Actions Gained From High-Density Electromyogram
doi: 10.1249/JES.0000000000000254.
Novel Insights Into Biarticular Muscle Actions Gained From High-Density Electromyogram
PMID: 33927163
PMCID: PMC8191471
Abstract
Biarticular muscles have traditionally been considered to exhibit homogeneous neuromuscular activation. The regional activation of biarticular muscles, as revealed from high-density surface electromyograms, seems however to discredit this notion. We thus hypothesize the regional activation of biarticular muscles may contribute to different actions about the joints they span. We then discuss the mechanistic basis and methodological implications underpinning our hypothesis.
Design and Characterization of a Textile Electrode System for the Detection of High-Density sEMG
doi: 10.1109/TNSRE.2021.3086860. Epub 2021 Jun 15.
Design and Characterization of a Textile Electrode System for the Detection of High-Density sEMG
PMID: 34097613
Abstract
Muscle activity monitoring in dynamic conditions is a crucial need in different scenarios, ranging from sport to rehabilitation science and applied physiology. The acquisition of surface electromyographic (sEMG) signals by means of grids of electrodes (High-Density sEMG, HD-sEMG) allows obtaining relevant information on muscle function and recruitment strategies. During dynamic conditions, this possibility demands both a wearable and miniaturized acquisition system and a system of electrodes easy to wear, assuring a stable electrode-skin interface. While recent advancements have been made on the former issue, detection systems specifically designed for dynamic conditions are at best incipient. The aim of this work is to design, characterize, and test a wearable, HD-sEMG detection system based on textile technology. A 32-electrodes, 15 mm inter-electrode distance textile grid was designed and prototyped. The electrical properties of the material constituting the detection system and of the electrode-skin interface were characterized. The quality of sEMG signals was assessed in both static and dynamic contractions. The performance of the textile detection system was comparable to that of conventional systems in terms of stability of the traces, properties of the electrode-skin interface and quality of the collected sEMG signals during quasi-isometric and highly dynamic tasks.
The Effect of Passive Exoskeleton on Shoulder Muscles Activity during Different Static Tasks
doi: 10.1016/j.jbiomech.2020.109685. Epub 2020 Feb 26.
Effect of continuous, mechanically passive, anti-gravity assistance on kinematics and muscle activity during dynamic shoulder elevation
Abstract
Passive shoulder exoskeletons, which provide continuous anti-gravitational force at the shoulder, could assist with dynamic shoulder elevation movements involved in activities of daily living and rehabilitation exercises. However, prior biomechanical studies of these exoskeletons primarily focused on static overhead tasks. In this study, we evaluated how continuous passive anti-gravity assistance affects able-bodied neuromuscular activity and shoulder kinematics during dynamic and static phases of shoulder elevation movements. Subjects, seated upright, elevated the shoulder from a rest posture (arm relaxed at the side) to a target shoulder elevation angle of 90°. Subjects performed the movement in the frontal (abduction) and scapular (scaption) planes with and without passive anti-gravity assistance. Muscles that contribute to positive shoulder elevation, based on their reported moment arms, had significantly lower muscle activations with assistance during both dynamic and static elevation. Muscles that contribute to negative shoulder elevation, which can decelerate the shoulder during dynamic shoulder elevation, were not significantly different between assistance conditions. This may be partly explained by the trend of subjects to reduce their maximum angular decelerations near the target to offset the positive shoulder elevation moment due to the anti-gravity assistance. Our results suggest that passive anti-gravity assistance could reduce the muscle activations needed to perform dynamic movements. Consequently, the anti-gravity assistance of passive shoulder exoskeletons may enhance motor function and reduce muscle and joint loads for both able-bodied and disabled users.
Keywords: Anti-gravity; Assistance; Exoskeleton; Passive; Shoulder.
Upper Limbs Musculoskeletal OpenSim Model: Customization and Assessment
Mechanisms and Machine Science
Volume 91, Pages 162 – 1702021
Upper Limbs Musculoskeletal OpenSim Model: Customization and Assessment
Abstract
Computational modelling is a powerful tool in biomechanical studies. Open-source software OpenSim provides different musculoskeletal models. However, existing upper body models consider only one limb, which could be a limitation in reproducing two-handed tasks. The purpose of this research was to develop a two upper limbs model that can be customized with subject’s anthropometry and muscles properties. The proposed model was composed of thorax, left and right upper limbs. Each limb presents 3 degrees of freedom (shoulder flexion-extension, elbow flexion-extension and prono-supination), 4 flexor and 3 extensor muscles. A preliminary model assessment was done. A subject was asked to execute isometric tests at three elbow angles, holding different loads, while EMG muscle activation was recorded. Simulated and experimental muscles activation were compared considering the right upper limb. Very good results were obtained without external load, whereas differences were observed when increasing the load; but, overall, model performance remained acceptable. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG.
Author keywords
The Accurate Assessment of Muscle Excitation Requires the Detection of Multiple Surface Electromyograms
doi: 10.1249/JES.0000000000000240.
The Accurate Assessment of Muscle Excitation Requires the Detection of Multiple Surface Electromyograms
Abstract
When sampling electromyograms (EMGs) with one pair of electrodes, it seems implicitly assumed the detected signal reflects the net muscle excitation. However, this assumption is discredited by observations of local muscle excitation. Therefore, we hypothesize that the accurate assessment of muscle excitation requires multiple EMG detection and consideration of electrode-fiber alignment. We advise prudence when drawing inferences from individually collected EMGs.
The M waves of the biceps brachii have a stationary (shoulder-like) component in the first phase: Implications and recommendations for M-wave analysis
doi: 10.1088/1361-6579/abb791.
The M waves of the biceps brachii have a stationary (shoulder-like) component in the first phase: implications and recommendations for M-wave analysis
PMID: 32916668
Abstract
Objective: We recently documented that compound muscle action potentials (M waves) recorded over the ‘pennate’ vastus lateralis showed a sharp deflection (named as a shoulder) in the first phase. Here, we investigated whether such a shoulder was also present in M waves evoked in a muscle with different architecture, such as the biceps brachii, with the purpose of elucidating the electrical origin of such afeature.
Approach: M waves evoked by maximal single shocks to the brachial plexus were recorded in monopolar and bipolar configurations from 72 individuals using large (10 mm diameter) electrodes and from eight individuals using small (1 mm diameter) electrodes arranged in a linear array. The changes in M-wave features at different locations along the muscle fiber direction were examined.
Main results: The shoulder was recognizable in most (87%) monopolar M waves, whereas it was rarely observed (6%) in bipolar derivations. Recordings made along the fiber direction showed that the shoulder was a stationary (non-propagating) feature, with short duration (spiky), which had positive polarity at all locations along the fibers. The latency of the shoulder (9.5 ± 0.5 ms) was significantly shorter than the estimated time taken for the action potentials to reach the biceps tendon (12.8 ms).
Significance: The shoulder must be generated by a dipole source, i.e. a source created at a fixed anatomical position, although the exact origin of this dipole is uncertain. Our results suggest that the shoulder may not be due to the end-of-fiber signals formed at the biceps brachii tendon. The shoulder is not related to any specific arrangement of muscle fibers, as it has been observed in both pennate and fusiform muscles. Being a stationary (non-propagating) component, the shoulder is not reliable for studying changes in sarcolemmal excitability, and thus should be excluded from the M-wave analysis.
2020
Tutorial. Surface EMG detection, conditioning and pre-processing: Best practices
doi: 10.1016/j.jelekin.2020.102440. Epub 2020 Jun 26.
Tutorial. Surface EMG detection, conditioning and pre-processing: Best practices
PMID: 32763743
Abstract
This tutorial is aimed primarily to non-engineers, using or planning to use surface electromyography (sEMG) as an assessment tool for muscle evaluation in the prevention, monitoring, assessment and rehabilitation fields. The main purpose is to explain basic concepts related to: (a) signal detection (electrodes, electrode-skin interface, noise, ECG and power line interference), (b) basic signal properties, such as amplitude and bandwidth, (c) parameters of the front-end amplifier (input impedance, noise, CMRR, bandwidth, etc.), (d) techniques for interference and artifact reduction, (e) signal filtering, (f) sampling and (g) A/D conversion, These concepts are addressed and discussed, with examples. The second purpose is to outline best practices and provide general guidelines for proper signal detection, conditioning and A/D conversion, aimed to clinical operators and biomedical engineers. Issues related to the sEMG origin and to electrode size, interelectrode distance and location, have been discussed in a previous tutorial. Issues related to signal processing for information extraction will be discussed in a subsequent tutorial.
Keywords: Artifact reduction; Electrodes; Electrode–skin impedance; Electromyography; Interference reduction; Kinesiology; Noise reduction; Physiotherapy; Signal conditioning; Teaching; Tutorial; sEMG acquisition; sEMG amplifier; sEMG detection.
Architectural changes in superficial and deep compartments of the tibialis anterior during electrical stimulation over different sites
doi: 10.1109/TNSRE.2020.3027037. Epub 2020 Nov 6.
Architectural Changes in Superficial and Deep Compartments of the Tibialis Anterior During Electrical Stimulation Over Different Sites
PMID: 32986557
Abstract
Electrical stimulation is widely used in rehabilitation to prevent muscle weakness and to assist the functional recovery of neural deficits. Its application is however limited by the rapid development of muscle fatigue due to the non-physiological motor unit (MU) recruitment. This issue can be mitigated by interleaving muscle belly (mStim) and nerve stimulation (nStim) to distribute the temporal recruitment among different MU groups. To be effective, this approach requires the two stimulation modalities to activate minimally-overlapped groups of MUs. In this manuscript, we investigated spatial differences between mStim and nStim MU recruitment through the study of architectural changes of superficial and deep compartments of tibialis anterior (TA). We used ultrasound imaging to measure variations in muscle thickness, pennation angle, and fiber length during mStim, nStim, and voluntary (Vol) contractions at 15% and 25% of the maximal force. For both contraction levels, architectural changes induced by nStim in the deep and superficial compartments were similar to those observed during Vol. Instead, during mStim superficial fascicles underwent a greater change compared to those observed during nStim and Vol, both in absolute magnitude and in their relative differences between compartments. These observations suggest that nStim results in a distributed MU recruitment over the entire muscle volume, similarly to Vol, whereas mStim preferentially activates the superficial muscle layer. The diversity between spatial recruitment of nStim and mStim suggests the involvement of different MU populations, which justifies strategies based on interleaved nerve/muscle stimulation to reduce muscle fatigue during electrically-induced contractions of TA.
A Survey on the Use and Barriers of Surface Electromyography in Neurorehabilitation
doi: 10.3389/fneur.2020.573616. eCollection 2020.
A Survey on the Use and Barriers of Surface Electromyography in Neurorehabilitation
PMID: 33123079
PMCID: PMC7566898
Abstract
Historical, educational, and technical barriers have been reported to limit the use of surface electromyography (sEMG) in clinical neurorehabilitation settings. In an attempt to identify, review, rank, and interpret potential factors that may play a role in this scenario, we gathered information on (1) current use of sEMG and its clinical potential; (2) professional figures primarily dealing with sEMG; (3) educational aspects, and (4) possible barriers and reasons for its apparently limited use in neurorehabilitation. To this aim, an online 30-question survey was sent to 52 experts on sEMG from diverse standpoints, backgrounds, and countries. Participants were asked to respond to each question on a 5-point Likert scale or by ranking items. A cut-off of 75% agreement was chosen as the consensus threshold. Thirty-five invitees (67%) completed the electronic survey. Consensus was reached for 77% of the proposed questions encompassing current trends in sEMG use in neurorehabilitation, educational, technical, and methodological features as well as its translational utility for clinicians and patients. Data evidenced the clinical utility of sEMG for patient assessment, to define the intervention plan, and to complement/optimize other methods used to quantify muscle and physical function. The aggregate opinion of the interviewed experts confirmed that sEMG is more frequently employed in technical/methodological than clinical research. Moreover, the slow dissemination of research findings and the lack of education on sEMG seem to prevent prompt transfer into practice. The findings of the present survey may contribute to the ongoing debate on the appropriateness and value of sEMG for neurorehabilitation professionals and its potential translation into clinical settings.
Keywords: clinical research; expert opinion; muscle activation; neurorehabilitation; sEMG; surface electromyography; survey.
Characterization of the stimulation output of four devices for focal muscle vibration
doi: 10.1016/j.medengphy.2020.10.002. Epub 2020 Oct 7.
Characterization of the stimulation output of four devices for focal muscle vibration
PMID: 33081969
Abstract
Different devices for mechano-acoustic muscle vibration became available on the market in the last ten years. Although the use of these vibrators is increasing in research and clinical settings, the features of their stimulation output were never described in literature. In this study we aimed to quantify and compare the stimulation output of the four most widespread pneumatic devices for focal muscle vibration available on the market. A piezoelectric pressure sensor was used to measure the pressure profile generated by the four selected devices in the following experimental conditions: i) measurement of the output changes associated with variations of the stimulation amplitude for three stimulation frequencies (100 Hz, 200 Hz, and 300 Hz); ii) measurement of the output changes during a 20-min long stimulation at constant frequency (300 Hz) and amplitude; iii) measurement of the output changes associated with the progressive activation of all stimulation channels at constant frequency (200 Hz) for different amplitudes. The maximum peak-to-peak amplitudes of the pressure waves were in the range 102 mbar – 369 mbar (below the maximum values declared by the different manufacturers). The shape of the pressure waves generated by the four devices was quasi-sinusoidal and asymmetric with respect to the atmospheric pressure. All output features had a remarkable intra- and inter-device variability. Further studies are required to support the technological improvement of the currently available devices and to focus the issues of vibration effectiveness, limitations, proper protocols, modalities of its application and assessment in neuromuscular training and rehabilitation.
Keywords: Focal muscle vibration; Mechanical stimulation; Rehabilitation.
Complexity analysis of surface electromyography for assessing the myoelectric manifestation of muscle fatigue: A review
doi: 10.3390/e22050529.
Complexity Analysis of Surface Electromyography for Assessing the Myoelectric Manifestation of Muscle Fatigue: A Review
PMID: 33286301
PMCID: PMC7517022
DOI: 10.3390/e22050529
Abstract
The surface electromyography (sEMG) records the electrical activity of muscle fibers during contraction: one of its uses is to assess changes taking place within muscles in the course of a fatiguing contraction to provide insights into our understanding of muscle fatigue in training protocols and rehabilitation medicine. Until recently, these myoelectric manifestations of muscle fatigue (MMF) have been assessed essentially by linear sEMG analyses. However, sEMG shows a complex behavior, due to many concurrent factors. Therefore, in the last years, complexity-based methods have been tentatively applied to the sEMG signal to better individuate the MMF onset during sustained contractions. In this review, after describing concisely the traditional linear methods employed to assess MMF we present the complexity methods used for sEMG analysis based on an extensive literature search. We show that some of these indices, like those derived from recurrence plots, from entropy or fractal analysis, can detect MMF efficiently. However, we also show that more work remains to be done to compare the complexity indices in terms of reliability and sensibility; to optimize the choice of embedding dimension, time delay and threshold distance in reconstructing the phase space; and to elucidate the relationship between complexity estimators and the physiologic phenomena underlying the onset of MMF in exercising muscles.
Keywords: approximate entropy; correlation dimension; detrended fluctuation analysis; fractal dimension; fuzzy entropy; largest Lyapunov exponent; recurrence quantification analysis; sEMG; sample entropy.
Force control during submaximal isometric contractions is associated with walking performance in persons with multiple sclerosis
2020 Jun 1;123(6):2191-2200.
doi: 10.1152/jn.00085.2020. Epub 2020 Apr 29.
Force control during submaximal isometric contractions is associated with walking performance in persons with multiple sclerosis
PMID: 32347151
PMCID: PMC7311722
Abstract
Individuals with multiple sclerosis (MS) experience progressive declines in movement capabilities, especially walking performance. The purpose of our study was to compare the amount of variance in walking performance that could be explained by the functional capabilities of lower leg muscles in persons with MS and a sex- and age-matched control group. Participants performed two walking tests (6-min walk and 25-ft walk), strength tests for the plantar flexor and dorsiflexor muscles, and steady submaximal (10% and 20% maximum) isometric contractions. High-density electromyography (EMG) was recorded during the steady contractions, and the signals were decomposed to identify the discharge times of concurrently active motor units. There were significant differences between the two groups in the force fluctuations during the steady contractions (force steadiness), the strength of the plantar flexor and dorsiflexor muscles, and the discharge characteristics during the steady contractions. Performance on the two walking tests by the MS group was moderately associated with force steadiness of the plantar flexor and dorsiflexor muscles; worse force steadiness was associated with poorer walking performance. In contrast, the performance of the control group was associated with muscle strength (25-ft test) and force steadiness of the dorsiflexors and variance in common input of motor units to the plantar flexors (6-min test). These findings indicate that a reduction in the ability to maintain a steady force during submaximal isometric contractions is moderately associated with walking performance of persons with MS.NEW & NOTEWORTHY The variance in walking endurance and walking speed was associated with force control of the lower leg muscles during submaximal isometric contractions in individuals with multiple sclerosis (MS). In contrast, the fast walking speed of a sex- and age-matched control group was associated with the strength of lower leg muscles. These findings indicate that moderate declines in the walking performance of persons with MS are more associated with impairments in force control rather than decreases in muscle strength.
Keywords: common drive; force steadiness; high-density EMG motor units; multiple sclerosis; walking.
Contraction level, but not force direction or wrist position, affects the spatial distribution of motor unit recruitment in the biceps brachii muscle
2020 Apr;120(4):853-860.
doi: 10.1007/s00421-020-04324-6. Epub 2020 Feb 19.
Contraction level, but not force direction or wrist position, affects the spatial distribution of motor unit recruitment in the biceps brachii muscle
PMID: 32076830
Abstract
Purpose: Different motor units (MUs) in the biceps brachii (BB) muscle have been shown to be preferentially recruited during either elbow flexion or supination. Whether these different units reside within different regions is an open issue. In this study, we tested wheter MUs recruited during submaximal isometric tasks of elbow flexion and supination for two contraction levels and with the wrist fixed at two different angles are spatially localized in different BB portions.
Methods: The MUs’ firing instants were extracted by decomposing high-density surface electromyograms (EMG), detected from the BB muscle of 12 subjects with a grid of electrodes (4 rows along the BB longitudinal axis, 16 columns medio-laterally). The firing instants were then used to trigger and average single-differential EMGs. The average rectified value was computed separately for each signal and the maximal value along each column in the grid was retained. The center of mass, defined as the weighted mean of the maximal, average rectified value across columns, was then consdiered to assess the medio-lateral changes in the MU surface representation between conditions.
Results: Contraction level, but neither wrist position nor force direction (flexion vs. supination), affected the spatial distribution of BB MUs. In particular, higher forces were associated with the recruitment of BB MUs whose action potentials were represented more medially.
Conclusion: Although the action potentials of BB MUs were represented locally across the muscle medio-lateral region, dicrimination between elbow flexion or supination seems unlikely from the surface representation of MUs action potentials.
Keywords: High-density EMG; Motor control; Motor units decomposition; Surface EMG.
Swallowing Onset Detection: Comparison of Endoscopy- and Accelerometry-Based Estimations
Volume 80, Pages 1053 – 10612021 8th European Medical and Biological Engineering Conference, EMBEC 2020Portorož29 November 2020 through 3 December 2020Code 252529
Swallowing Onset Detection: Comparison of Endoscopy- and Accelerometry-Based Estimations
PMID: 31760455
Abstract
The swallowing process involves the coordinated activation of several muscles to ensure the transfer of nutrients from the mouth to the stomach. A proper segmentation of swallowing into its constituent phases is relevant to obtain a quantitative biomechanical and electrophysiological description of this sensorimotor task. The aim of the study was to design a non-invasive measurement framework integrating electromyographic and acceleration measurements to detect the swallowing onset and event-related muscular symmetry indexes during the oropharyngeal phase. Therefore, the experimental protocol included: surface electromyography (sEMG), accelerometry and Fiberoptic Endoscopic Examination of Swallowing (FEES) as a clinical gold standard. A comparative study on five healthy subjects was performed in order to evaluate the results of the accelerometer-based segmentation with respect to those obtained through the gold standard. Results showed that the accelerometer-based method consistently underestimated the swallowing onset (204 ± 192 ms, mean and standard deviation). Despite this bias towards the onset estimation, sEMG symmetry indexes computed from the accelerometer- and FEES-based onset exhibited comparable values. These preliminary results suggest that the observed underestimation is not relevant in order to study symmetry differences in swallowing muscular activation. Thus, the acceleration measurements can provide a possible non-invasive alternative to the FEES-based segmentation for the extraction of event-related symmetry indexes during the oropharyngeal phase of swallowing. © 2021, Springer Nature Switzerland AG.
Author keywords
Accelerometry; FEES; sEMG; Swallowing muscles; Symmetry indexes
Regional modulation of the ankle plantarflexor muscles associated with standing external perturbations across different directions
doi: 10.1007/s00221-019-05696-8. Epub 2019 Nov 23.
Regional modulation of the ankle plantarflexor muscles associated with standing external perturbations across different directions
PMID: 31760455
Abstract
Maintenance of upright standing posture has often been explained using the inverted pendulum model. This model considers the ankle plantarflexors to act as a single synergistic group. There are differences in muscle properties among the medial and lateral gastrocnemius (MG and LG, respectively) and the soleus that may affect their activation. Twelve volunteers participated in an investigation to determine whether the activation of the ankle plantarflexor muscles was modulated according to perturbation direction during unilateral standing perturbations of 1% body mass. High-density surface electromyography (HDS-EMG) was used to determine the amplitude and barycenter of the muscle activation and kinematic analysis was used to evaluate ankle, knee, and hip joint movement. The HDS-EMG amplitude and barycenter of MG and LG were modulated with the perturbation direction (MG p < 0.05; LG p < 0.01; one-way repeated-measures ANOVA). In soleus, the HDS-EMG barycenter modulated across the perturbation direction (p < 0.01 for X&Y coordinates), but the HDS-EMG amplitude did not change. A repeated-measures correlation was used to interpret the HDS-EMG pattern in the context of the kinematics. The relative contribution of MG activation compared to the total gastrocnemii activation was significantly associated with ankle dorsi/plantarflexion (rrm = 0.620), knee flexion/extension and abduction/adduction (rrm = 0.622 and rrm = 0.547, respectively), and hip flexion/extension and abduction/adduction (rrm = 0.653 and rrm = 0.432, respectively). The findings suggest that the central nervous system activates motor units within different regions of MG, LG and SOL in response to standing perturbations in different directions.
Keywords: High-density surface electromyography; Plantarflexors; Regional modulation; Standing posture.
The peripheral origin of tap-induced muscle contraction revealed by multi-electrode surface electromyography in human vastus medialis
doi: 10.1038/s41598-020-59122-z.
The peripheral origin of tap-induced muscle contraction revealed by multi-electrode surface electromyography in human vastus medialis
PMID: 32041996
PMCID: PMC7010771
Abstract
It is well established that muscle percussion may lead to the excitation of muscle fibres. It is still debated, however, whether the excitation arises directly at the percussion site or reflexively, at the end plates. Here we sampled surface electromyograms (EMGs) from multiple locations along human vastus medialis fibres to address this issue. In five healthy subjects, contractions were elicited by percussing the distal fibre endings at different intensities (5-50 N), and the patellar tendon. EMGs were detected with two 32-electrode arrays, positioned longitudinally and transversally to the percussed fibres, to detect the origin and the propagation of action potentials and their spatial distribution across vastus medialis. During muscle percussion, compound action potentials were first observed at the electrode closest to the tapping site with latency smaller than 5 ms, and spatial extension confined to the percussed strip. Conversely, during tendon tap (and voluntary contractions), action potentials were first detected by electrodes closest to end plates and at a greater latency (mean ± s.d., 28.2 ± 1.7 ms, p < 0.001). No evidence of reflex responses to muscle tap was observed. Multi-electrode surface EMGs allowed for the first time to unequivocally and quantitatively describe the non-reflex nature of the response evoked by a muscle tap.
Timing and Modulation of Activity in the Lower Limb Muscles During Indoor Rowing: What Are the Key Muscles to Target in FES-Rowing Protocols?
doi: 10.3390/s20061666.
Timing and Modulation of Activity in the Lower Limb Muscles During Indoor Rowing: What Are the Key Muscles to Target in FES-Rowing Protocols?
PMID: 32192073
PMCID: PMC7147320
DOI: 10.3390/s20061666
Abstract
The transcutaneous stimulation of lower limb muscles during indoor rowing (FES Rowing) has led to a new sport and recreation and significantly increased health benefits in paraplegia. Stimulation is often delivered to quadriceps and hamstrings; this muscle selection seems based on intuition and not biomechanics and is likely suboptimal. Here, we sample surface EMGs from 20 elite rowers to assess which, when, and how muscles are activated during indoor rowing. From EMG amplitude we specifically quantified the onset of activation and silencing, the duration of activity and how similarly soleus, gastrocnemius medialis, tibialis anterior, rectus femoris, vastus lateralis and medialis, semitendinosus, and biceps femoris muscles were activated between limbs. Current results revealed that the eight muscles tested were recruited during rowing, at different instants and for different durations. Rectus and biceps femoris were respectively active for the longest and briefest periods. Tibialis anterior was the only muscle recruited within the recovery phase. No side differences in the timing of muscle activity were observed. Regression analysis further revealed similar, bilateral modulation of activity. The relevance of these results in determining which muscles to target during FES Rowing is discussed. Here, we suggest a new strategy based on the stimulation of vasti and soleus during drive and of tibialis anterior during recovery.
Keywords: electromyography; functional electrical stimulation; muscle; rowing.
Upper limbs cranking for post-stroke rehabilitation: A pilot study on healthy subjects
IEEE Medical Measurements and Applications, MeMeA 2020 – Conference Proceedings
June 2020 Article number 913728215th IEEE International Symposium on Medical Measurements and Applications, MeMeA 2020Bari1 June 2020 through 3 June 2020Code 161821
Upper limbs cranking for post-stroke rehabilitation: A pilot study on healthy subjects
PMID: 32192073
PMCID: PMC7147320
DOI: 10.3390/s20061666
Abstract
Since one of the major consequences of stroke is hemiparesis, the rehabilitation of upper limbs is necessary to improve the quality of life. Arm cranking gesture represents an alternative rehabilitation tool, especially if accompanied by a biofeedback involving and motivating patients. The aim of this pilot study was twofold: (1) to evaluate the effect of a visual and virtual biofeedback on arm cranking gesture and (2) to estimate the duration of pull and push phases of the crank cycle. Nine healthy and young subjects were involved in the test and were asked to perform the arm cranking gesture in different conditions. A stereophotogrammetric system was adopted to create a virtual, visual and real time biofeedback of cadence, to measure the real cadence of participants and to estimate push and pull phases durations. Results showed that the biofeedback helped subjects to follow an externally imposed cadence. Furthermore, the pull phase resulted to be slightly longer than the push one, although the angular amplitude of the two phases suggested they were the same. © 2020 IEEE.
Author keywords
2019
A Modular, Smart, and Wearable System for High Density sEMG Detection
doi: 10.1109/TBME.2019.2904398. Epub 2019 Mar 11.
A Modular, Smart, and Wearable System for High Density sEMG Detection
Abstract
Objective: The use of linear or bi-dimensional electrode arrays for surface EMG detection (HD-sEMG) is gaining attention as it increases the amount and reliability of information extracted from the surface EMG. However, the complexity of the setup and the encumbrance of HD-sEMG hardware currently limits its use in dynamic conditions. The aim of this paper was to develop a miniaturized, wireless, and modular HD-sEMG acquisition system for applications requiring high portability and robustness to movement artifacts.
Methods: A system with modular architecture was designed. Its core is a miniaturized 32-channel amplifier (Sensor Unit – SU) sampling at 2048 sps/ch with 16 bit resolution and wirelessly transmitting data to a PC or a mobile device. Each SU is a node of a Body Sensor Network for the synchronous signal acquisition from different muscles.
Results: A prototype with two SUs was developed and tested. Each SU is small (3.4 cm × 3 cm × 1.5 cm), light (16.7 g), and can be connected directly to the electrodes; thus, avoiding the need for customary, wired setup. It allows to detect HD-sEMG signals with an average noise of 1.8 μVRMS and high performance in terms of rejection of power-line interference and motion artefacts. Tests performed on two SUs showed no data loss in a 22 m range and a ±500 μs maximum synchronization delay.
Conclusions: Data collected in a wide spectrum of experimental conditions confirmed the functionality of the designed architecture and the quality of the acquired signals.
Significance: By simplifying the experimental setup, reducing the hardware encumbrance, and improving signal quality during dynamic contractions, the developed system opens new perspectives in the use of HD-sEMG in applied and clinical settings.
A tendon-like orthosis actuated by shape memory alloy wires and controlled by myoelectric signals: A single-finger prototype.
BIOSYSTEMS & BIOROBOTICS
A Tendon-Like Orthosis Actuated by Shape Memory Alloy Wires and Controlled by Myoelectric Signals: A Single-Finger Prototype
Abstract
People of industrialized countries are living longer and consequently the incidence of disability… coming from medical conditions such as stroke is increasing. The hand rehabilitation process following a stroke accident requires very intense rehabilitation sessions. It is crucial to improve the outcomes of hand physical therapy by providing patients with an orthosis aid designed to assist their movement and performing the role of exercising the hand during the early stages of recovery. The aim of this work is to describe the system architecture and the mechanical design of a new tendon-like orthosis actuated by shape memory alloy (SMA) wires and controlled by myoelectric signals.
Challenging Standing Balance Reduces the Asymmetry of Motor Control of Postural Sway Poststroke
2019 Jul 1;23(3):327-343.
doi: 10.1123/mc.2017-0098. Epub 2019 Jan 1.
Challenging Standing Balance Reduces the Asymmetry of Motor Control of Postural Sway Poststroke
PMID: 30599808
DOI: 10.1123/mc.2017-0098
Abstract
Background: Ankle plantarflexor muscle impairment contributes to asymmetrical postural control poststroke. Objective: This study examines the relationship of plantarflexor electromyography (EMG) with anterior-posterior center of pressure (APCOP) in people poststroke during progressive challenges to standing balance. Methods: Ten people poststroke and 10 controls participated in this study. Anteriorly directed loads of 1% body mass (BM) were applied to the pelvis every 25-40 s until 5%BM was reached. Cross-correlation values between plantarflexor EMG and APCOP (EMG:APCOP) position and velocity were compared. Results: EMG:APCOP velocity correlations were stronger than EMG:APCOP position across all muscles (p < .01), and correlations were predominately stronger in the nonparetic compared with the paretic leg (p < .05). Increasing challenge to standing balance reduced asymmetry of EMG:APCOP relationships. Conclusions: These data suggest that sensory information reflected in APCOP velocity interacts more strongly with plantarflexor activity in people poststroke and controls than APCOP position. Furthermore, increasing challenge to standing balance reduces postural control asymmetry between legs poststroke.
Keywords: paresis; plantarflexors; postural control; stroke.
Development and testing of acoustically-matched hydrogel-based electrodes for simultaneous EMG-ultrasound detection
2019 Feb;64:74-79.
doi: 10.1016/j.medengphy.2018.12.002. Epub 2018 Dec 14.
Development and testing of acoustically-matched hydrogel-based electrodes for simultaneous EMG-ultrasound detection
PMID: 30554980
Abstract
In this manuscript we describe the development and testing of a bipolar electrode for the simultaneous acquisition of ultrasound (US) images and surface electromyograms (EMGs) from the same muscle region. The developed electrode (bEMG-US) consists of two circular sensing regions (20 mm diameter) with fixed inter-electrode distance (3.5 cm, center-to-center). Both the sensing regions and the external structure of the electrode are made of hydrogel layers separated by insulating materials. The electrical properties (i.e., impedance and noise of the electrode-skin interface) and the quality of EMGs detected with the developed electrodes during electrically elicited contractions were assessed and compared with those provided by commercially available EMG electrodes. The effect of the bEMG-US electrode on US images was evaluated by comparing images detected from the same muscle region with and without the electrode interposed between the US probe and the skin. Tests on five subjects showed that the electrode-skin impedance of bEMG-US electrodes was higher than that of conventional EMG electrodes (mean (range): 15.6 (8.5-21.1) kΩ vs. 8.2 (4.9-16.5) kΩ). Despite higher impedance values, both electrode systems provided comparable, electrode-skin noise levels (1.4 (1.1-1.7) µV vs. 1.3 (1.0-1.5) µV) and M waves (normalized mean square error: 2.6 (0.6-6.8)%). The quality of US images detected with and without the bEMG-US electrode between the US probe and the skin was comparable, as demonstrated by the low errors in the estimation of anatomical variables in the two experimental conditions (range: (0.37-2.35) deg for pennation angle and (-0.31-0.1) cm for muscle thickness). Results demonstrate that bEMG-US can be used to acquire concurrently EMGs and US images from the same muscle region with a negligible effect on the quality of the two detected signals, thus allowing for a simultaneous, multimodal evaluation of muscle activation.
Keywords: Electrode; Electrode-skin impedance; Muscle architecture; Surface EMG; Ultrasound imaging.
Identification of muscle fasciculations from surface EMG: comparison with ultrasound-based detection
doi: 10.1109/EMBC.2019.8857873.
Identification of muscle fasciculations from surface EMG: comparison with ultrasound-based detection
PMID: 31947010
Abstract
The clinical standard for the identification of muscle fasciculations is needle electromyography. However, both surface electromyograms (sEMG) and ultrasound imaging (US) have been recently proposed as alternative and more sensitive approaches. The aims of this study were to: (i) compare the sensitivity to muscle fasciculations of sEMG and US, (ii) assess the rate of agreement (RoA) between the two approaches, and (iii) investigate how much sensitivity and RoA are affected by the selectivity of sEMG detection. Surface EMGs were collected concurrently with US images using an array of 32 electrodes spanning the whole, posterior aspect of the leg. Muscle fasciculations were identified from US videos and from monopolar and single differential sEMGs computed between electrodes spaced by 1, 2, and 3 cm. Results from five healthy subjects showed that US detected as many fasciculations as single differential EMGs, but always less than monopolar sEMGs. However, monopolar sEMGs exhibited a very poor spatial selectivity, likely responsible for the small RoA with US measures. The RoA was maximal for single differential recordings with 3cm inter-electrode distance, however, it was always smaller than 75% (median=30%). Although preliminary, these results suggest that sEMG and US are sensitive to different events in the muscle volume and that their integration may increase the detection sensitivity to muscle fasciculations.
Innervation zone locations distribute medially within the pectoralis major muscle during bench press exercise
doi: 10.1016/j.jelekin.2019.03.002. Epub 2019 Mar 7.
Innervation zone locations distribute medially within the pectoralis major muscle during bench press exercise
Abstract
Changes in innervation zone (IZ) position may affect the amplitude of surface electromyograms (EMGs). If not accounted for, these changes may lead to equivocal interpretation on the degree of muscle activity from EMG amplitude. In this study we ask how much the IZ position changes within different regions of the pectoralis major (PM) during the bench press exercise. If expressive, changes in IZ position may explain the conflictual results reported on PM activation during bench press. Single-differential surface EMGs were collected from 15 regions along the PM cranial, centro-cranial, centro-caudal and caudal fibres, while 11 healthy participants gently, isometrically contracted their muscle. IZs were identified visually, from EMGs collected with the glenohumeral joint at extreme bench press positions; 20° and 110° of abduction in the horizontal plane. Except for 3 out of 88 acquisitions (4 detection sites × 2 glenohumeral angles × 11 participants), for which no phase opposition and action potential propagation were observed, IZs could be well identified. Group results revealed the IZ moved medially from 110° to 20° of glenohumeral joint abduction in the horizontal plane, regardless of the PM region from where EMGs were detected (P < 0.01). IZs were confined medially within PM, from ∼20% to ∼40% of the muscle-tendon unit length, and their position changed up to 13.3%. These results suggest that changes in the amplitude of EMGs detected mainly medially from PM may be not associated with changes in the degree of PM activity during bench press.
Keywords: Isometric contractions; Resistance training; Surface electromyography.
Motor neuron degeneration, severe myopathy and TDP-43 increase in a transgenic pig model of SOD1-linked familiar ALS
doi: 10.1016/j.nbd.2018.11.021. Epub 2018 Nov 22.
Motor neuron degeneration, severe myopathy and TDP-43 increase in a transgenic pig model of SOD1-linked familiar ALS
PMID: 30471417
Abstract
Amyotrophic Lateral Sclerosis (ALS) is a neural disorder gradually leading to paralysis of the whole body. Alterations in superoxide dismutase SOD1 gene have been linked with several variants of familial ALS. Here, we investigated a transgenic (Tg) cloned swine model expressing the human pathological hSOD1G93A allele. As in patients, these Tg pigs transmitted the disease to the progeny with an autosomal dominant trait and showed ALS onset from about 27 months of age. Post mortem analysis revealed motor neuron (MN) degeneration, gliosis and hSOD1 protein aggregates in brainstem and spinal cord. Severe skeletal muscle pathology including necrosis and inflammation was observed at the end stage, as well. Remarkably, as in human patients, these Tg pigs showed a quite long presymptomatic phase in which gradually increasing amounts of TDP-43 were detected in peripheral blood mononuclear cells. Thus, this transgenic swine model opens the unique opportunity to investigate ALS biomarkers even before disease onset other than testing novel drugs and possible medical devices.
Keywords: ALS; Amyotrophic lateral sclerosis; SOD1; TDP-43; Transgenic pig.
Postural muscle unit plasticity in stroke survivors: Altered distribution of gastrocnemius’ action potentials
doi: 10.3389/fneur.2019.00686. eCollection 2019.
Postural Muscle Unit Plasticity in Stroke Survivors: Altered Distribution of Gastrocnemius’ Action Potentials
Abstract
Neuromuscular adaptations are well-reported in stroke survivors. The death of motor neurons and the reinnervation of residual muscle fibers by surviving motor neurons, for example, seem to explain the increased density of muscle units after stroke. It is, however, unknown whether reinnervation takes place locally or extensively within the muscle. Here we combine intramuscular and surface electromyograms (EMGs) to address this issue for medial gastrocnemius (MG); a key postural muscle. While seven stroke survivors stood upright, two intramuscular and 15 surface EMGs were recorded from the paretic and non-paretic gastrocnemius. Surface EMGs were triggered with the firing instants of motor units identified through the decomposition of both intramuscular and surface EMGs. The standard deviation of Gaussian curves fitting the root mean square amplitude distribution of surface potentials was considered to assess differences in the spatial distribution of motor unit action potentials and, thus, in the distribution of muscle units between limbs. The median number of motor units identified per subject in the paretic and non-paretic sides was, respectively, 2 (range: 1-3) and 3 (1-4). Action potentials in the paretic gastrocnemius were represented at a 33% wider skin region when compared to the non-paretic muscle (Mann-Whitney; P = 0.014). Side differences in the representation of motor unit were not associated with differences in subcutaneous thickness (skipped-Spearman r = -0.53; confidence interval for r: -1.00 to 0.63). Current results suggest stroke may lead to the enlargement of the gastrocnemius muscle units recruited during standing. The enlargement of muscle units, as assessed from the skin surface, may constitute a new marker of neuromuscular plasticity following stroke.
Keywords: electromyogram; gastrocnemius; motor unit; standing; stroke.
Potentiation of the first and second phases of the M wave after maximal voluntary contractions in the biceps brachii muscle
2019 Oct;57(10):2231-2244.
doi: 10.1007/s11517-019-02025-7. Epub 2019 Aug 13.
Potentiation of the first and second phases of the M wave after maximal voluntary contractions in the biceps brachii muscle
PMID: 31410691
Abstract
The study was undertaken to examine separately the potentiation of the first and second phases of the M wave in biceps brachii after conditioning maximal voluntary contractions (MVCs) of different durations. M waves were evoked in the biceps brachii muscle before and after isometric MVCs of 1, 3, 6, 10, 30, and 60 s. The amplitude, duration, and area of the first and second phases of monopolar M waves were measured during the 10-min period following each contraction. Our results indicated that the amplitude and area of the M-wave first phase increased after MVCs of long (≥ 30 s) duration (P < 0.05), while it decreased after MVCs of short (≤ 10 s) duration (P < 0.05). The enlargement after the long MVCs persisted for 5 min, whereas the depression after the short contractions lasted only for 15 s. The amplitude of the second phase increased immediately (1 s) after all MVCs tested (P < 0.05), regardless of their duration, and then returned rapidly (10 s) to control levels. Unexpectedly, the amplitude of the second phase decreased below control values between 15 s and 1 min after the MVCs lasting ≥ 6 s (P < 0.05). Our results reinforce the idea that the presence of fatigue is a necessary condition to induce an enlargement of the M-wave first phase and that this enlargement would be greater (and occur sooner) in muscles with a predominance of type II fibers (quadriceps and biceps brachii) compared to type-I predominant muscles (tibialis anterior). The unique findings observed for the M-wave second phase indicate that changes in this phase are highly muscle dependent. Graphical abstract Left panel-Representative examples of M waves recorded in one participant before (control) and at various times after conditioning maximal voluntary contractions (MVCs) of short (a1) and long (a2) duration. Left panel-Time course of recovery of the amplitude of the first (b1) and second (b2) phases of the M wave after conditioning MVCs of different durations.
Keywords: Biceps brachii; Brachial plexus stimulation; Electromyography; Isometric contraction; M wave; M-wave potentiation.
Validation of Polymer-Based Screen-Printed Textile Electrodes for Surface EMG Detection
doi: 10.1109/TNSRE.2019.2916397. Epub 2019 May 23.
Validation of Polymer-Based Screen-Printed Textile Electrodes for Surface EMG Detection
PMID: 31144638
Abstract
In recent years, the variety of textile electrodes developed for electrophysiological signal detection has increased rapidly. Among the applications that could benefit from this advancement, those based on surface electromyography (sEMG) are particularly relevant in rehabilitation, training, and muscle function assessment. In this work, we validate the performance of polymer-based screen-printed textile electrodes for sEMG signal detection. We obtained these electrodes by depositing poly-3,4-ethylenedioxythiophene doped with poly(styrene sulfonate) (PEDOT:PSS) onto cotton fabric, and then selectively changing the physical properties of the textile substrate. The manufacturing costs are low and this process meets the requirements of textile-industry production lines. The validation of these electrodes was based on their functional and electrical characteristics, assessed for two different electrode sizes and three skin-interface conditions (dry, solid hydrogel, or saline solution), and compared to those of conventional disposable gelled electrodes. Results show high similarity in terms of noise amplitude and electrode-skin impedance between the conventional and textile electrodes with the addition of solid hydrogel or saline solution. Furthermore, we compared the shape of the electrically induced sEMG, as detected by conventional and textile electrodes from tibialis anterior. The comparison yielded an [Formula: see text] value higher than 97% for all measurement conditions. Preliminary tests in dynamic conditions (walking) revealed the exploitability of the proposed electrode technology with saline application for the monitoring of sEMG for up to 35 min of activity. These results suggest that the proposed screen-printed textile electrodes may be an effective alternative to the conventional gelled electrodes for sEMG acquisition, thereby providing new opportunities in clinical and wellness fields.
Wearable and Wireless HD-sEMG Acquisition Systems: Recent Advances
In Biosystems and Biorobotics (Vol. 21)
Wearable and Wireless HD-sEMG Acquisition Systems: Recent Advances
Abstract
Multi-channel sEMG techniques open new perspectives in the non-invasive assessment of neuromuscular system but currently, can be applied only during isometric or dynamic tasks because of the encumbrance of existing sEMG acquisition systems and their sensitivity to movement artefacts. The aim of this work is to describe a new, wireless, wearable, and modular multi-channel sEMG acquisition system for the study of the neuromuscular system during highly-dynamic tasks.
2018
Contralateral effect of short-duration unilateral neuromuscular electrical stimulation and focal vibration in healthy subjects
doi: 10.23736/S1973-9087.18.05004-9. Epub 2018 Mar 12.
Contralateral effect of short-duration unilateral neuromuscular electrical stimulation and focal vibration in healthy subjects
Abstract
Background: The “contralateral effect” phenomenon refers to the strength gain in the opposite, untrained homonymous muscle following unilateral training. Previous studies showed that neuromuscular electrical stimulation (NMES) of the right quadriceps facilitated maximal voluntary strength and efferent neural drive of the left knee extensors, while no previous study investigated the contralateral effect elicited by focal muscle vibration.
Aim: The aim of this study was to investigate whether quadriceps NMES and focal vibration, when applied unilaterally, have the same potential to enhance the contralateral muscle strength and the associated neural drive.
Design: Randomized controlled experimental study.
Setting: University laboratory.
Population: Healthy subjects.
Methods: Subjects completed several maximal voluntary contractions (MVCs) of the left quadriceps (tested muscle) while the right quadriceps (treated muscle) received no conditioning stimulation (control condition), NMES or focal vibration. Paired supramaximal stimuli were delivered to the left quadriceps during and immediately after the MVCs to assess voluntary activation. The EMG activity of vastus lateralis, vastus medialis, and rectus femoris muscles of the left quadriceps was also concomitantly recorded.
Results: MVC torque and voluntary activation of the left quadriceps increased during contralateral NMES and vibration. A remarkable inter-individual variability was observed in the contralateral effect of NMES and vibration. In fact, MVC and voluntary activation increases were particularly evident in subjects “responders” to both treatments (who showed NMES-elicited increases in MVC and voluntary activation of 22.5% and 15.8%, respectively, and vibration-elicited increases of 13.1% and 10.7%, respectively). Moreover, we found that the increases in voluntary activation and EMG activity elicited by NMES were higher than those elicited by focal vibration. We also found that voluntary activation increases were higher in subjects presenting lower baseline levels of voluntary activation.
Conclusions: The short-duration unilateral application of quadriceps NMES and focal vibration increased MVC torque and efferent neural drive of the contralateral homologous muscle in healthy subjects.
Clinical rehabilitation impact: As the two physical therapy modalities can be useful to maximize motor unit recruitment contralaterally to the side of application, they could be incorporated in rehabilitation protocols when unilateral voluntary contractions are uncomfortable, painful or not feasible.
Design and Test of a Biomechanical Model for the Estimation of Knee Joint Angle During Indoor Rowing: Implications for FES-Rowing Protocols in Paraplegia
2018 Nov;26(11):2145-2152.
doi: 10.1109/TNSRE.2018.2876634. Epub 2018 Oct 17.
Design and Test of a Biomechanical Model for the Estimation of Knee Joint Angle During Indoor Rowing: Implications for FES-Rowing Protocols in Paraplegia
PMID: 30334801
Abstract
Functional electrical stimulation of lower limb muscles during rowing provides a means for the cardiovascular conditioning in paraplegia. The possibility of shaping stimulation profiles according to changes in knee angle, so far conceived as changes in seat position, may help circumventing open issues associated with muscle fatigue and movement coordination. Here, we present a subject-specific biomechanical model for the estimation of knee joint angle during indoor rowing. Anthropometric measurements and foot and seat positions are inputs to the model. We tested our model on two samples of elite rowers; 15 able-bodied, and 11 participants in the Rio 2016 Paralympic games. Paralympic rowers presented minor physical disabilities (LTA-PD classification), enabling them to perform the full rowing cycle (with legs, trunks, and arms). Knee angle was estimated from the rowing machine seat position, measured with a linear encoder, and transmitted wirelessly to a computer. Key results indicate the root mean square error (RMSE) between estimated and measured angles did not depend on group and stroke rate ( ). Significantly greater RMSE values were observed, however, within the rowing cycle ( ), reaching on average 8 deg in the mid-recovery phase. Differences between estimated and measured knee angle values resulted in slightly earlier (5%) detection of knee flexion, regardless of the group and stroke rate considered. Offset of knee extension, knee angle at catch and range of knee motion were identified equally well with our model and with inertial sensors. These results suggest our model describes accurately the movement of knee joint during indoor rowing.
Does the activity of ankle plantar flexors differ between limbs while healthy, young subjects stand at ease?
2018 Nov 16;81:140-144.
doi: 10.1016/j.jbiomech.2018.09.018. Epub 2018 Sep 21.
Does the activity of ankle plantar flexors differ between limbs while healthy, young subjects stand at ease?
Abstract
Inferences on the active contribution of plantar flexors to the stabilisation of human standing posture have been drawn from surface electromyograms (EMGs). Surface EMGs were however often detected unilaterally, presuming the myoelectric activity from muscles in a single leg reflects the pattern of muscle activation in both legs. In this study we question whether surface EMGs detected from plantar flexor muscles in both legs provide equal estimates of the duration of activity. Arrays of surface electrodes were used to collect EMGs from gastrocnemius and soleus muscles while twelve, young male participants stood at ease for 60 s. Muscles in each leg were deemed active whenever the Root Mean Square amplitude of EMGs (40 ms epochs) detected by any channel in the arrays exceeded the noise level, defined from EMGs detected during rest. The Chi-Square statistics revealed significant differences in the relative number of active periods for both muscles in 10 out of 12 participants tested, ranging from 2% to 65% (χ2 > 17.90; P < 0.01). Pearson correlation analysis indicated side differences in the duration of gastrocnemius though not soleus activity were associated with the centre of pressure mean, lateral position (R = 0.60; P = 0.035). These results suggest therefore that surface EMGs may provide different estimates of the timing of plantar flexors’ activity if collected unilaterally during standing and that asymmetric activation may be not necessarily associated with weight distribution between limbs. Depending on the body side from which EMGs are collected, the active contribution of plantar flexors to standing stabilization may be either under- or over-valued.
Keywords: Center of pressure; Electromyography; Postural control; Standing; Triceps surae.
Does the amplitude of biceps brachii M waves increase similarly in both limbs during staircase, electrically elicited contractions?
2018 Aug 20;39(8):085005.
doi: 10.1088/1361-6579/aad57c.
Does the amplitude of biceps brachii M waves increase similarly in both limbs during staircase, electrically elicited contractions?
PMID: 30039799
Abstract
Objective: Humans usually tend to control more finely muscle force production in dominant than non-dominant upper limbs. It is well established that motor unit recruitment is a key mechanism by which muscle force is controlled, and we hypothesized that a relatively smaller number of motor units may be recruited in muscles of dominant than non-dominant limbs for any given increase in synaptic input. Hence, we investigated peripheral properties of dominant and non-dominant biceps brachii through the analysis of M-wave responses to incremental electrical stimulation.
Approach: Current pulses at progressively greater intensities were applied in the proximal region of biceps brachii of 16 subjects while surface electromyograms were recorded with a grid of electrodes in the distal region. M-wave amplitude was averaged across channels and normalized with respect to the maximum amplitude value, separately for each stimulation intensity and limb. Amplitude-current intensity curves were interpolated to provide an equal number of stimulation levels between limbs. Differences between dominant and non-dominant arms were assessed through the average increase in M-wave amplitude for consecutive stimulation intensities (increments).
Main results: Wilcoxon’s signed-rank test showed that increments in the M-wave amplitude were significantly smaller (p = 0.017) in dominant than non-dominant biceps brachii.
Significance: The results suggest that there was a more gradual recruitment of motor units in biceps brachii of dominant than non-dominant arms. This is in agreement with the hypothesis of a broader spectrum of motor unit recruitment thresholds in the dominant arm, which may contribute to a finer regulation of force production.
Effect of TMS coil orientation on the spatial distribution of motor evoked potentials in an intrinsic hand muscle
doi: 10.1515/bmt-2016-0240.
Effect of TMS coil orientation on the spatial distribution of motor evoked potentials in an intrinsic hand muscle
PMID: 28796636
Abstract
Previous reports on the relationship between coil orientation and amplitude of motor evoked potential (MEP) in transcranial magnetic stimulation (TMS) did not consider the effect of electrode arrangement. Here we explore this open issue by investigating whether TMS coil orientation affects the amplitude distribution of MEPs recorded from the abductor pollicis brevis (APB) muscle with a bi-dimensional grid of 61 electrodes. Moreover, we test whether conventional mono- and bipolar montages provide representative MEPs compared to those from the grid of electrodes. Our results show that MEPs with the greatest amplitudes were elicited for 45° and 90° coil orientations, i.e. perpendicular to the central sulcus, for all electrode montages. Stimulation with the coil oriented at 135° and 315°, i.e. parallel to the central sulcus, elicited the smallest MEP amplitudes. Additionally, changes in coil orientation did not affect the spatial distribution of MEPs over the muscle extent. It has been shown that conventional electrodes with detection volume encompassing the APB belly may detect representative MEPs for optimal coil orientations. In turn, non-optimal orientations were identified only with the grid of electrodes. High-density electromyography may therefore provide new insights into the effect of coil orientation on MEPs from the APB muscle.
Keywords: brain stimulation; conventional electrodes; electric field direction; high-density electromyography; muscle imaging; transcranial magnetic stimulation.
Electrical nerve stimulation modulates motor unit activity in contralateral biceps brachii during steady isometric contractions
doi: 10.1152/jn.00235.2018. Epub 2018 Aug 29.
Electrical nerve stimulation modulates motor unit activity in contralateral biceps brachii during steady isometric contractions
Free article
Abstract
The purpose of our study was to compare the influence of five types of electrical nerve stimulation delivered through electrodes placed over the right biceps brachii on motor unit activity in the left biceps brachii during an ongoing steady isometric contraction. The electrical stimulation protocols comprised different combinations of pulse duration (0.2 and 1.0 ms), stimulus frequency (50 and 90 Hz), and stimulus current (greater or less than motor threshold). The electrical nerve stimulation protocols were applied over the muscle of the right elbow flexors of 13 participants (26 ± 3 yr) while they performed voluntary contractions with the left elbow flexors to match a target force set at 10% of maximum. All five types of electrical nerve stimulation increased the absolute amplitude of the electromyographic (EMG) signal recorded from the left biceps brachii with high-density electrodes. Moreover, one stimulation condition (1 ms, 90 Hz) had a consistent influence on the centroid location of the EMG amplitude distribution and the average force exerted by the left elbow flexors. Another stimulation condition (0.2 ms, 90 Hz) reduced the coefficient of variation for force during the voluntary contraction, and both low-frequency conditions (50 Hz) increased the duration of the mean interspike interval of motor unit action potentials after the stimulation had ended. The findings indicate that the contralateral effects of electrical nerve stimulation on the motor neuron pool innervating the homologous muscle can be influenced by both stimulus pulse duration and stimulus frequency. NEW & NOTEWORTHY Different types of electrical nerve stimulation delivered through electrodes placed over the right biceps brachii modulated the ongoing motor unit activity in the left biceps brachii. Although the effects varied with stimulus pulse duration, frequency, and current, all five types of electrical nerve stimulation increased the amplitude of the electromyographic activity in the left biceps brachii. Moreover, most of the effects in the left arm occurred after the electrical nerve stimulation of the right arm had been terminated.
Keywords: barycenter; force steadiness; high-density surface EMG; interspike interval.
Interpreting Signal Amplitudes in Surface Electromyography Studies in Sport and Rehabilitation Sciences
doi: 10.3389/fphys.2017.00985. eCollection 2017.
Interpreting Signal Amplitudes in Surface Electromyography Studies in Sport and Rehabilitation Sciences
Abstract
Surface electromyography (sEMG) is a popular research tool in sport and rehabilitation sciences. Common study designs include the comparison of sEMG amplitudes collected from different muscles as participants perform various exercises and techniques under different loads. Based on such comparisons, researchers attempt to draw conclusions concerning the neuro- and electrophysiological underpinning of force production and hypothesize about possible longitudinal adaptations, such as strength and hypertrophy. However, such conclusions are frequently unsubstantiated and unwarranted. Hence, the goal of this review is to discuss what can and cannot be inferred from comparative research designs as it pertains to both the acute and longitudinal outcomes. General methodological recommendations are made, gaps in the literature are identified, and lines for future research to help improve the applicability of sEMG are suggested.
Keywords: activation; excitation; exercise; hypertrophy; motor unit recruitment; muscle force; rate coding; strength.
Localised sampling of myoelectric activity may provide biased estimates of cocontraction for gastrocnemius though not for soleus and tibialis anterior muscles
doi: 10.1016/j.jelekin.2017.11.003. Epub 2017 Nov 14.
Localised sampling of myoelectric activity may provide biased estimates of cocontraction for gastrocnemius though not for soleus and tibialis anterior muscles
- PMID: 29156320
- DOI: 10.1016/j.jelekin.2017.11.003
Abstract
Proper muscle activity quantification is highly relevant to monitor and treat spastic cocontraction. As activity may distribute unevenly within muscle volumes, particularly for pennate calf muscles, surface electromyograms (EMGs) detected by traditional bipolar montage may provide biased estimations of muscle activity. We compared cocontraction estimates obtained using bipolar vs grids of electrodes (high-density EMG, HD-EMG). EMGs were collected from medial gastrocnemius, soleus and tibialis anterior during isometric plantar and dorsi-flexion efforts at three levels (30%, 70% and 100% MVC), knee flexed and extended. Cocontraction index (CCI) was estimated separately for each electrode pair in the grid. While soleus and tibialis anterior CCI estimates did not depend on the detection system considered, for gastrocnemius bipolar electrodes provided larger cocontraction estimates than HD-EMG at highest effort levels, at both knee angles (ANOVA; P < .001). Interestingly, HD-EMG detected greater gastrocnemius EMGs distally during plantar flexions, and greater CCI values proximally during dorsiflexions. These results suggest that bipolar electrodes: (i) provide reliable estimates of soleus and tibialis anterior cocontraction; (ii) may under-or overestimate gastrocnemius cocontraction, depending on their distal or proximal position.
Keywords: Bipolar electrodes; Gastrocnemius; Soleus; Spastic cocontraction; Surface EMG.
Is the firing rate of motor units in different vastus medialis regions modulated similarly during isometric contractions?
doi: 10.1002/mus.25688. Epub 2017 May 29.
Is the firing rate of motor units in different vastus medialis regions modulated similarly during isometric contractions?
PMID: 28500671
DOI: 10.1002/mus.25688
Abstract
Introduction: Previous evidence suggests the fibers of different motor units reside within distinct vastus medialis (VM) regions. It remains unknown whether the activity of these motor units may be modulated differently. Herein we assess the discharge rate of motor units detected proximodistally from the VM to address this issue.
Methods: Surface electromyograms (EMGs) were recorded proximally and distally from the VM while 10 healthy subjects performed isometric contractions. Single motor units were decomposed from surface EMGs. The smoothed discharge rates of motor units identified from the same and from different VM regions were then cross-correlated.
Results: During low-level contractions, the discharge rate varied more similarly for distal (cross-correlation peak; interquartile interval: 0.27-0.40) and proximal (0.28-0.52) than for proximodistal pairs of VM motor units (0.20-0.33; P = 0.006).
Discussion: The discharge rates of motor units from different proximodistal VM regions show less similarity in their variations than those of pairs of units either distally or proximally. Muscle Nerve 57: 279-286, 2018.
Keywords: compartmentalization; knee; motor unit; quadriceps; surface electromyography; vastus medialis.
Motor unit discharge characteristics and walking performance of individuals with multiple sclerosis
doi: 10.1152/jn.00598.2017. Epub 2018 Jan 3.
Motor unit discharge characteristics and walking performance of individuals with multiple sclerosis
PMID: 29357453
PMCID: PMC5966731
Abstract
Walking performance of persons with multiple sclerosis (MS) is strongly influenced by the activation signals received by lower leg muscles. We examined the associations between force steadiness and motor unit discharge characteristics of lower leg muscles during submaximal isometric contractions with tests of walking performance and disability status in individuals who self-reported walking difficulties due to MS. We expected that worse walking performance would be associated with weaker plantar flexor muscles, worse force steadiness, and slower motor unit discharge times. Twenty-three individuals with relapsing-remitting MS (56 ± 7 yr) participated in the study. Participants completed one to three evaluation sessions that involved two walking tests (25-ft walk and 6-min walk), a manual dexterity test (grooved pegboard), health-related questionnaires, and measurement of strength, force steadiness, and motor unit discharge characteristics of lower leg muscles. Multiple regression analyses were used to construct models to explain the variance in measures of walking performance. There were statistically significant differences (effect sizes: 0.21-0.60) between the three muscles in mean interspike interval (ISI) and ISI distributions during steady submaximal contractions with the plantar flexor and dorsiflexor muscles. The regression models explained 40% of the variance in 6-min walk distance and 47% of the variance in 25-ft walk time with two or three variables that included mean ISI for one of the plantar flexor muscles, dorsiflexor strength, and force steadiness. Walking speed and endurance in persons with relapsing-remitting MS were reduced in individuals with longer ISIs, weaker dorsiflexors, and worse plantar flexor force steadiness. NEW & NOTEWORTHY The walking endurance and gait speed of persons with relapsing-remitting multiple sclerosis (MS) were worse in individuals who had weaker dorsiflexor muscles and greater force fluctuations and longer times between action potentials discharged by motor units in plantar flexor muscles during steady isometric contractions. These findings indicate that the control of motor unit activity in lower leg muscles of individuals with MS is associated with their walking ability.
Keywords: 25-ft walk; 6-min walk; force steadiness; motor units; multiple sclerosis; muscle strength.
Motor units in vastus lateralis and in different vastus medialis regions show different firing properties during low-level, isometric knee extension contraction
doi: 10.1016/j.humov.2017.12.012. Epub 2017 Dec 28.
Motor units in vastus lateralis and in different vastus medialis regions show different firing properties during low-level, isometric knee extension contraction
PMID: 29289349
Abstract
Architectural differences along vastus medialis (VM) and between VM and vastus lateralis (VL) are considered functionally important for the patellar tracking, knee joint stability and knee joint extension. Whether these functional differences are associated with a differential activity of motor units between VM and VL is however unknown. In the present study, we, therefore, investigate neuroanatomical differences in the activity of motor units detected proximo-distally from VM and from the VL muscle. Nine healthy volunteers performed low-level isometric knee extension contractions (20% of their maximum voluntary contraction) following a trapezoidal trajectory. Surface electromyograms (EMGs) were recorded from VM proximal and distal regions and from VL using three linear adhesive arrays of eight electrodes. The firing rate and recruitment threshold of motor units decomposed from EMGs were then compared among muscle regions. Results show that VL motor units reached lower mean firing rates in comparison with VM motor units, regardless of their position within VM (P < .040). No significant differences in firing rate were found between proximal and distal, VM motor units (P = .997). Furthermore, no significant differences in the recruitment threshold were observed for all motor units analysed (P = .108). Our findings possibly suggest the greater potential of VL to generate force, due to its fibres arrangement, may account for the lower discharge rate observed for VL then either proximally or distally detected motor units in VM. Additionally, the present study opens new perspectives on the importance of considering muscle architecture in investigations of the neural aspects of motor behaviour.
Keywords: Motor unit; Quadriceps; Surface electromyography; Vastus lateralis; Vastus medialis.
Neural Correlates to the Increase in Maximal Force after Dexamethasone Administration
doi: 10.1249/MSS.0000000000001425.
Neural Correlates to the Increase in Maximal Force after Dexamethasone Administration
PMID: 28930864
Abstract
Purpose: This study investigated the effects of short-term glucocorticoid administration on voluntary activation and intracortical inhibitory and facilitatory circuits.
Methods: Seventeen healthy men participated in a pseudorandomized double-blind study to receive either dexamethasone (8 mg·d, n = 9 subjects) or placebo (n = 8 subjects) for 7 d. The ankle dorsiflexion torque, corresponding EMG of the tibialis anterior, and voluntary activation assessed by the interpolated twitch method using transcranial magnetic stimulation (TMS) were measured during a maximal voluntary contraction (MVC). Short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed at rest and during submaximal contraction (50% MVC torque) by paired-pulse TMS with the conditioning stimulus set at 0.8× of motor threshold and delivered 2 ms (SICI) and 13 ms (ICF) before the test stimulus (1.2× motor threshold).
Results: The MVC torque (+14%), tibialis anterior EMG (+31%), and voluntary activation (+3%) increased after glucocorticoid treatment (P < 0.05). The increase in voluntary activation was associated with the gain in MVC torque (r = 0.56; P = 0.032). The level of SICI and the duration of the EMG silent period that followed the test TMS decreased (-18.6% and -13.5%, respectively) during the 50% MVC after treatment (P < 0.05), whereas no significant change was observed for ICF. Neither SICI nor ICF changed after treatment when assessed at rest.
Conclusions: Short-term dexamethasone treatment induced specific decrease in the excitability of intracortical inhibitory circuits that likely contributed to the increase in the voluntary activation and associated MVC torque.
2017
Surface EMG and muscle fatigue: multi-channel approaches to the study of myoelectric manifestations of muscle fatigue. Gazzoni, Marco; Botter, Alberto; Martins, Taian. Physiological measurement. 2017; 27-60, ISSN: 0967-3334
doi: 10.1088/1361-6579/aa60b9. Epub 2017 Feb 15.
Surface EMG and muscle fatigue: multi-channel approaches to the study of myoelectric manifestations of muscle fatigue
Changes in tibialis anterior architecture affect the amplitude of surface electromyograms. Vieira TM, Bisi MC, Stagni R, Botter A. J Neuroeng Rehabil. 2017 Aug 14;14(1):81
Changes in tibialis anterior architecture affect the amplitude of surface electromyograms.
Author information
- 1
- Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics and Telecommunication, Politecnico di Torino, Via Cavalli 22/h, 10138, Torino, Italy. taian.vieira@polito.it.
- 2
- Department of Electrical, Electronic and Information Engineering “Guglielmo Marconi”, University of Bologna, Viale Risorgimento 2, Bologna, 40136, Italy.
- 3
- Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics and Telecommunication, Politecnico di Torino, Via Cavalli 22/h, 10138, Torino, Italy.
Abstract
BACKGROUND:
Variations in the amplitude of surface electromyograms (EMGs) are typically considered to advance inferences on the timing and degree of muscle activation in different circumstances. Surface EMGs are however affected by factors other than the muscle neural drive. In this study, we use electrical stimulation to investigate whether architectural changes in tibialis anterior (TA), a key muscle for balance and gait, affect the amplitude of surface EMGs.
METHODS:
Current pulses (500 μs; 2 pps) were applied to the fibular nerve of ten participants, with the ankle at neutral, full dorsi and full plantar flexion positions. Ultrasound images were collected to quantify changes in TA architecture with changes in foot position. The peak-to-peak amplitude of differential M waves, detected with a grid of surface electrodes (16 × 4 electrodes; 10 mm inter-electrode distance), was considered to assess the effect of changes in TA architecture on the surface recordings.
RESULTS:
On average, both TA pennation angle and width increased by respectively 7 deg. and 9 mm when the foot moved from plantar to dorsiflexion (P < 0.02). M-wave amplitudes changed significantly with ankle position. M waves elicited in dorsiflexion and neutral positions were ~25% greater than those obtained during plantar flexion, regardless of where they were detected in the grid (P < 0.001). This figure increased to ~50% when considering bipolar M waves.
CONCLUSIONS:
Findings reported here indicate the changes in EMG amplitude observed during dynamic contractions, especially when changes in TA architecture are expected (e.g., during gait), may not be exclusively conceived as variations in TA activation.
KEYWORDS:
Electrical stimulation; Surface electromyograms; Tibialis anterior; Ultrasound
- PMID:
- 28807025
- DOI:
- 10.1186/s12984-017-0291-5
Is the firing rate of motor units in different vastus medialis regions modulated similarly during isometric contractions? Cabral HV, de Souza LML, Mello RGT, Gallina A, de Oliveira LF, Vieira TM. Muscle Nerve. 2017 May 13
Is the firing rate of motor units in different vastus medialis regions modulated similarly during isometric contractions?
Abstract
INTRODUCTION:
Previous evidence suggests the fibers of different motor units reside within distinct vastus medialis (VM) regions. It remains unknown whether the activity of these motor units may be modulated differently. Herein we assess the discharge rate of motor units detected proximodistally from the VM to address this issue.
METHODS:
Surface electromyograms (EMGs) were recorded proximally and distally from the VM while 10 healthy subjects performed isometric contractions. Single motor units were decomposed from surface EMGs. The smoothed discharge rates of motor units identified from the same and from different VM regions were then cross-correlated.
RESULTS:
During low-level contractions, the discharge rate varied more similarly for distal (cross-correlation peak; interquartile interval: 0.27-0.40) and proximal (0.28-0.52) than for proximodistal pairs of VM motor units (0.20-0.33; P = 0.006).
CONCLUSIONS:
The discharge rates of motor units from different proximodistal VM regions show less similarity in their variations than those of pairs of units either distally or proximally. Muscle Nerve, 2017.
© 2017 Wiley Periodicals, Inc.
KEYWORDS:
compartmentalization; knee; motor unit; quadriceps; surface electromyography; vastus medialis
- PMID:
- 28500671
- DOI:
- 10.1002/mus.25688
Is heart rate variability affected by distinct motor imagery strategies? Peixoto Pinto T, Mello Russo Ramos M, Lemos T, Domingues Vargas C, Imbiriba LA. Physiol Behav. 2017 Aug 1;177:189-195.
Is heart rate variability affected by distinct motor imagery strategies?
Abstract
Although some studies have reported significant changes in autonomic responses according to the perspective-taking during motor imagery [first person perspective (1P) and third person perspective (3P)], investigations on how the strategies adopted to mentally simulate a given movement affect the heart rate variability (HRV) seem so far unexplored. Twenty healthy subjects mentally simulated the movement of middle-finger extension in 1P and 3P, while electrocardiogram was recorded. After each task, the level of easiness was self-reported. Motor imagery ability was also assessed through the revised version of Movement Imagery Questionnaire (MIQ-R) and a mental chronometry index. The traditional measures of HRV in the time- and frequency-domain were compared between 1P and 3P tasks by using Student’s t-test for dependent samples. The MIQ-R results showed that subjects had the same facility to imagine movements in 1P or 3P. The mental chronometry index revealed a similar temporal course only between 1P and execution, while the 3P strategy had a shorter duration. Additionally, the subjective report was similar between the experimental tasks. Regarding the HRV measures, the low frequency component, in log-transformed unit, was significantly higher (p=0.017) in 1P than 3P, suggesting a higher activity of the sympathetic system during 1P. This log-transformed HRV parameter seems to be more sensitive than normalized values for the assessment of the motor imagery ability, together with questionnaires, scales and mental chronometry.
Copyright © 2017 Elsevier Inc. All rights reserved.
KEYWORDS:
Autonomic nervous system; Heart rate variability; Motor imagery strategies
- PMID:
- 28476285
- DOI:
- 10.1016/j.physbeh.2017.05.004
Physiological arousal accompanying postural responses to external perturbations after stroke. Pollock CL, Carpenter MG, Hunt MA, Gallina A, Vieira TM, Ivanova TD, Garland SJ. Clin Neurophysiol. 2017 Jun;128(6):935-944
Physiological arousal accompanying postural responses to external perturbations after stroke.
Author information
- 1
- Department of Physical Therapy, University of British Columbia, Vancouver, Canada.
- 2
- School of Kinesiology, University of British Columbia, Vancouver, Canada.
- 3
- Department of Physical Therapy, University of British Columbia, Vancouver, Canada; Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Italy.
- 4
- Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Italy; Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
- 5
- Faculty of Health Sciences, Western University, London, Canada.
- 6
- Faculty of Health Sciences, Western University, London, Canada. Electronic address: jgarland@uwo.ca.
Abstract
OBJECTIVE:
The purpose of this study was to examine simultaneously the level of physiological arousal and the postural response to external perturbations in people post-stroke compared to age-matched controls to build a more comprehensive understanding of the effect of stroke on postural control and balance self-efficacy.
METHODS:
Participants stood with each foot on separate force platforms. Ten applications of loads of 2% body weight at the hips perturbed the participant anteriorly under two conditions: investigator-triggered or self-triggered (total 20). Electrodermal activity (EDA; measurement of physiological arousal), electromyography (EMG) of the ankle plantarflexor muscles and anterior-posterior center of pressure measurements were taken pre-perturbation (anticipatory) and post-perturbation (response) and compared between the initial (first two) and final (last two) perturbations.
RESULTS:
Participants post-stroke demonstrated significantly higher levels of anticipatory EDA and anticipatory paretic plantarflexor EMG during both self- and investigator-triggered conditions compared to controls. Anticipatory EDA levels were higher in the final perturbations in participants post-stroke in both conditions, but not in controls. Habituation of the EDA responses post-perturbation was exhibited in the self-triggered perturbations in controls, but not in participants post-stroke.
CONCLUSIONS:
Physiological arousal and postural control strategies of controls revealed habituation in response to self-triggered perturbations, whereas this was not seen in participants post-stroke.
SIGNIFICANCE:
Understanding the physiological arousal response to challenges to standing balance post-stroke furthers our understanding of postural control mechanisms post-stroke.
Copyright © 2017. Published by Elsevier B.V.
KEYWORDS:
External perturbation; Physiological arousal; Postural control; Stroke
- PMID:
- 28407522
- DOI:
- 10.1016/j.clinph.2017.03.008
Optimization of surface electrodes location for H-reflex recordings in soleus muscle. Botter A, Vieira TM. J Electromyogr Kinesiol. 2017 Jun;34:14-23
Optimization of surface electrodes location for H-reflex recordings in soleus muscle.
Author information
- 1
- Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy. Electronic address: alberto.botter@polito.it.
- 2
- Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.
Abstract
The Hoffmann reflex (H reflex) is extensively used to investigate the spinal motor neuron excitability in healthy and pathological subjects. Obtaining a representative and robust amplitude estimation of the H reflex is of marked relevance in clinical as well as in research applications. As for the motor responses, this issue is strictly related to the electrode positioning, especially for large, pinnate muscles such as the triceps surae. In this study we investigated the effect of electrode position on soleus H-reflex amplitude. A grid of 96 electrodes was used to identify maximal H reflexes (Hmax) across the whole soleus region available for surface recording. The spatial distribution of Hmax amplitude detected in monopolar and single-differential derivations was used to determine where greatest reflex responses were detected from soleus. For both derivations and for all participants, largest Hmax were detected consistently over the central soleus region, in correspondence of the muscle superficial aponeurosis. Indeed, the amplitude of Hmax provided by conventional electrodes (1cm2 area, 2cm apart) located centrally was significantly greater (median: 35% for monopolar and 79% for single-differential derivations) than that obtained medially, where surface electromyograms are typically recorded from soleus. Computer simulations, used to assist in the interpretation of results, suggest the soleus pinnate architecture was the key determinant of the medio-lateral variability observed for the experimental Hmax. The presented results provide a clear indication for electrode positioning, of crucial relevance in applied studies aimed at eliciting H reflexes.
Copyright © 2017 Elsevier Ltd. All rights reserved.
KEYWORDS:
Achilles tendon; EMG; Electrode positioning; H reflex; Soleus
- PMID:
- 28342367
- DOI:
- 10.1016/j.jelekin.2017.03.003
Is myoelectric activity distributed equally within the rectus femoris muscle during loaded, squat exercises? de Souza LM, da Fonseca DB, Cabral HD, de Oliveira LF, Vieira TM. J Electromyogr Kinesiol. 2017 Apr;33:10-19
Is myoelectric activity distributed equally within the rectus femoris muscle during loaded, squat exercises?
Author information
- 1
- Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
- 2
- Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
- 3
- Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. Electronic address: liliam@peb.ufrj.br.
- 4
- Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.
Abstract
Recent evidence suggests different regions of the rectus femoris (RF) muscle respond differently to squat exercises. Such differential adaptation may result from neural inputs distributed locally within RF, as previously reported for isometric contractions, walking and in response to fatigue. Here we therefore investigate whether myoelectric activity distributes evenly within RF during squat. Surface electromyograms (EMGs) were sampled proximally and distally from RF with arrays of electrodes, while thirteen healthy volunteers performed 10 consecutive squats with 20% and 40% of their body weight. The root mean square (RMS) value, computed separately for thirds of the concentric and eccentric phases, was considered to assess the proximo-distal changes in EMG amplitude during squat. The channels with variations in EMG amplitude during squat associated with shifts in the muscle innervation zone were excluded from analysis. No significant differences were observed between RF regions when considering squat phases and knee joint angles individually (P>0.16) while a significant interaction between phase and knee joint angle with detection site was observed (P<0.005). For the two loads considered, proximal RMS values were greater during the eccentric phase and for the more flexed knee joint position (P<0.001). Our results suggest inferences on the degree of RF activation during squat must be made cautiously from surface EMGs. Of more practical relevance, there may be a potential for the differential adaption of RF proximal and distal regions to squat exercises.
Copyright © 2017 Elsevier Ltd. All rights reserved.
KEYWORDS:
Rectus femoris; Resistance training; Squat; Surface electromyography
- PMID:
- 28110043
- DOI:
- 10.1016/j.jelekin.2017.01.003
The Spatial Distribution of Ankle Muscles Activity Discriminates Aged from Young Subjects during Standing. Dos Anjos FV, Pinto TP, Gazzoni M, Vieira TM. Front Hum Neurosci. 2017 Apr 19;11:190
The Spatial Distribution of Ankle Muscles Activity Discriminates Aged from Young Subjects during Standing.
Author information
- 1
- Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di TorinoTorino, Italy.
Abstract
During standing, age-related differences in the activation of ankle muscles have been reported from surface electromyograms (EMGs) sampled locally. Given though activity seems to distribute unevenly within ankle muscles, the local sampling of surface EMGs may provide a biased view on how often and how much elderly and young individuals activate these muscles during standing. This study aimed therefore at sampling EMGs from multiple regions of individual ankle muscles to evaluate whether the distribution of muscle activity differs between aged and young subjects during standing. Thirteen young and eleven aged, healthy subjects were tested. Surface EMGs were sampled at multiple skin locations from tibialis anterior, soleus and medial and lateral gastrocnemius muscles while subjects stood at ease. The root mean square amplitude of EMGs was considered to estimate the duration, the degree of activity and the size of the region where muscle activity was detected. Our main findings revealed the medial gastrocnemius was active for longer periods in aged (interquartile interval; 74.1-98.2%) than young (44.9-81.9%) individuals (P = 0.02). Similarly, while tibialis anterior was rarely active in young (0.7-4.4%), in elderly subjects (2.6-82.5%) it was often recruited (P = 0.01). Moreover, EMGs with relatively higher amplitude were detected over a significantly wider proximo-distal region of medial gastrocnemius in aged (29.4-45.6%) than young (20.1-31.3%) subjects (P = 0.04). These results indicate the duration and the size of active muscle volume, as quantified from the spatial distribution of surface EMGs, may discriminate aged from young individuals during standing; elderlies seem to rely more heavily on the active loading of ankle muscles to control their standing posture than young individuals. Most importantly, current results suggest different conclusions on the active control of standing posture may be drawn depending on the skin location from where EMGs are collected, in particular for the medial gastrocnemius.
KEYWORDS:
aging; electromyography; muscle activity; postural control; standing
- PMID:
- 28469567
- PMCID:
- PMC5395606
- DOI:
- 10.3389/fnhum.2017.00190
Spatial variation and inconsistency between estimates of onset of muscle activation from EMG and ultrasound. Dieterich AV, Botter A, Vieira TM, Peolsson A, Petzke F, Davey P, Falla D. Sci Rep. 2017 Feb 8;7:42011. doi: 10.1038/srep42011
Spatial variation and inconsistency between estimates of onset of muscle activation from EMG and ultrasound.
Author information
- 1
- Pain Clinic, Anaesthesiology, University Medical Center, Göttingen, Germany.
- 2
- Laboratory of Engineering of the Neuromuscular System and Motor Rehabilitation, Department of Electronics, Politecnico di Torino, Torino, Italy.
- 3
- School of Physical Education and Sports, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
- 4
- Department of Medical and Health Sciences, Physiotherapy, Linköping University, Linköping, Sweden.
- 5
- School of Physiotherapy and Exercise Science, Faculty of Health Sciences, Curtin University, Perth, Australia.
- 6
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK.
Abstract
Delayed onset of muscle activation can be a descriptor of impaired motor control. Activation onset can be estimated from electromyography (EMG)-registered muscle excitation and from ultrasound-registered muscle motion, which enables non-invasive measurements in deep muscles. However, in voluntary activation, EMG- and ultrasound-detected activation onsets may not correspond. To evaluate this, ten healthy men performed isometric elbow flexion at 20% to 70% of their maximal force. Utilising a multi-channel electrode transparent to ultrasound, EMG and M(otion)-mode ultrasound were recorded simultaneously over the biceps brachii muscle. The time intervals between automated and visually estimated activation onsets were correlated with the regional variation of EMG and muscle motion onset, contraction level and speed. Automated and visual onsets indicated variable time intervals between EMG- and motion onset, median (interquartile range) 96 (121) ms and 48 (72) ms, respectively. In 17% (computed analysis) or 23% (visual analysis) of trials, motion onset was detected before local EMG onset. Multi-channel EMG and M-mode ultrasound revealed regional differences in activation onset, which decreased with higher contraction speed (Spearman ρ ≥ 0.45, P < 0.001). In voluntary activation the heterogeneous motor unit recruitment together with immediate motion transmission may explain the high variation of the time intervals between local EMG- and ultrasound-detected activation onset.
2016
Spatial distribution of surface EMG on trapezius and lumbar muscles of violin and cello players in single note playing. Afsharipour B, Petracca F, Gasparini M, Merletti R. J Electromyogr Kinesiol. 2016 Dec;31:144-153
Spatial distribution of surface EMG on trapezius and lumbar muscles of violin and cello players in single note playing.
Author information
- 1
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, United States; Department of Physical Medicine and Rehabilitation of Northwestern University, United States; Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: babak.afsharipour@northwestern.edu.
- 2
- Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: fra.petra.fp@gmail.com.
- 3
- Department of Mathematical Sciences, Politecnico di Torino, Torino, Italy. Electronic address: mauro.gasparini@polito.it.
- 4
- Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: roberto.merletti@polito.it.
Abstract
Musicians activate their muscles in different patterns, depending on their posture, the instrument being played, and their experience level. Bipolar surface electrodes have been used in the past to monitor such activity, but this method is highly sensitive to the location of the electrode pair. In this work, the spatial distribution of surface EMG (sEMG) of the right trapezius and right and left erector spinae muscles were studied in 16 violin players and 11 cello players. Musicians played their instrument one string at a time in sitting position with/without backrest support. A 64 sEMG electrode (16×4) grid, 10mm inter-electrode distance (IED), was placed over the middle and lower trapezius (MT and LT) of the bowing arm. Two 16×2 electrode grids (IED=10mm) were placed on the left and right erector spinae muscles. Subjects played each of the four strings of the instrument either in large (1bow/s) or detaché tip/tail (8bows/s) bowing in two sessions (two days). In each of two days, measurements were repeated after half an hour of exercise to see the effect of exercise on the muscle activity and signal stability. A “muscle activity index” (MAI) was defined as the spatial average of the segmented active region of the RMS map. Spatial maps were automatically segmented using the watershed algorithm and thresholding. Results showed that, for violin players, sliding the bow upward from the tip toward the tail results in a higher MAI for the trapezius muscle than a downward bow. On the contrary, in cello players, higher MAI is produced in the tail to tip movement. For both instruments, an increasing MAI in the trapezius was observed as the string position became increasingly lateral, from string 1 (most medial) toward string 4 (most lateral). Half an hour of performance did not cause significant differences between the signal quality and the MAI values measured before and after the exercise. The MAI of the left and right erector spinae was smaller in the case of backrest support, especially for violin players. Back muscles of violin and cello players were activated asymmetrically, specifically in fast movements (detaché tip/tail). These findings demonstrate the sensitivity and stability of the technique and justify more extensive investigation following this proof of concept.
Copyright © 2016 Elsevier Ltd. All rights reserved.
KEYWORDS:
Cello; Erector spinae; High density surface electromyography (HDsEMG); Musicians; String players; Surface EMG; Trapezius; Violin
- PMID:
- 27835831
- DOI:
- 10.1016/j.jelekin.2016.10.003
Does the type of visual feedback information change the control of standing balance? Dos Anjos F, Lemos T, Imbiriba LA. Eur J Appl Physiol. 2016 Sep;116(9):1771-9
Does the type of visual feedback information change the control of standing balance?
Abstract
PURPOSE:
The aim of this study was to evaluate whether different types of visual feedback influence the control of standing balance.
METHODS:
Twenty-six subjects performed three tasks on a force platform: (1) standing with eyes open; (2) maintaining the own center of pressure (COP) displacement (internal feedback) on a target; and (3) pointing with a handheld laser pointer (external feedback) on a target. The COP and ankle displacements were measured through a force platform and a biaxial electrogoniometer, respectively, during 60 s in each task. Global posturographic parameters were computed in the anterior-posterior and medial-lateral directions. In addition, the standard deviation and mean frequency of the ankle movements were also calculated in the sagittal plane.
RESULTS:
The sway area and standard deviation of COP differed between conditions, wherein smaller and higher values were typically observed during the internal and external feedback, respectively. Conversely, both the mean frequency and the mean velocity of COP were greater during internal feedback compared with other tasks, while external feedback usually leads to smaller values. Additionally, smaller and higher values for the ankle standard deviation and the ankle mean frequency, respectively, were observed during internal feedback, with the external feedback condition showing an opposite behavior.
CONCLUSIONS:
These results showed that the global postural sway and the postural adjustments at ankle during standing balance change depending on the type of visual feedback information.
KEYWORDS:
Ankle motion; Postural control; Posturography; Visual feedback
- PMID:
- 27431210
- DOI:
- 10.1007/s00421-016-3434-7
Is there sufficient evidence to claim muscle units are not localised and functionally grouped within the human gastrocnemius? Vieira TM, Wakeling JM, Hodson-Tole EF. J Physiol. 2016 Apr 1;594(7):1953-4.
Is there sufficient evidence to claim muscle units are not localised and functionally grouped within the human gastrocnemius?
Author information
- 1
- Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Politecnico di Torino, Torino, Italia. taian.vieira@polito.it.
- 2
- Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil. taian.vieira@polito.it.
- 3
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Canada.
- 4
- School of Healthcare Science, Manchester Metropolitan University, Manchester, UK.
Comment in
Comment on
- PMID:
- 27038106
- PMCID:
- PMC4818604
- DOI:
- 10.1113/JP271866
Young, Healthy Subjects Can Reduce the Activity of Calf Muscles When Provided with EMG Biofeedback in Upright Stance. Vieira TM, Baudry S, Botter A. Front Physiol. 2016 Apr 29;7:158. doi: 10.3389/fphys.2016.00158. eCollection 2016.
Young, Healthy Subjects Can Reduce the Activity of Calf Muscles When Provided with EMG Biofeedback in Upright Stance.
Author information
- 1
- Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di TorinoTorino, Italia; Escola de Educação Física e Desportos, Departamento de Arte Corporal, Universidade Federal do Rio de JaneiroRio de Janeiro, Brasil.
- 2
- Laboratory of Applied Biology and Neurophysiology, ULB Neuroscience Institute, Université libre de Bruxelles Brussels, Belgium.
- 3
- Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino Torino, Italia.
Abstract
Recent evidence suggests the minimization of muscular effort rather than of the size of bodily sway may be the primary, nervous system goal when regulating the human, standing posture. Different programs have been proposed for balance training; none however has been focused on the activation of postural muscles during standing. In this study we investigated the possibility of minimizing the activation of the calf muscles during standing through biofeedback. By providing subjects with an audio signal that varied in amplitude and frequency with the amplitude of surface electromyograms (EMG) recorded from different regions of the gastrocnemius and soleus muscles, we expected them to be able to minimize the level of muscle activation during standing without increasing the excursion of the center of pressure (CoP). CoP data and surface EMG from gastrocnemii, soleus and tibialis anterior muscles were obtained from 10 healthy participants while standing at ease and while standing with EMG biofeedback. Four sensitivities were used to test subjects’ responsiveness to the EMG biofeedback. Compared with standing at ease, the two most sensitive feedback conditions induced a decrease in plantar flexor activity (~15%; P < 0.05) and an increase in tibialis anterior EMG (~10%; P < 0.05). Furthermore, CoP mean position significantly shifted backward (~30 mm). In contrast, the use of less sensitive EMG biofeedback resulted in a significant decrease in EMG activity of ankle plantar flexors with a marginal increase in TA activity compared with standing at ease. These changes were not accompanied by greater CoP displacements or significant changes in mean CoP position. Key results revealed subjects were able to keep standing stability while reducing the activity of gastrocnemius and soleus without loading their tibialis anterior muscle when standing with EMG biofeedback. These results may therefore posit the basis for the development of training protocols aimed at assisting subjects in more efficiently controlling leg muscle activity during standing.
KEYWORDS:
balance; biofeedback; electromyography; postural sway; standing
- PMID:
- 27199773
- PMCID:
- PMC4850153
- DOI:
- 10.3389/fphys.2016.00158
Between-day reliability of triceps surae responses to standing perturbations in people post-stroke and healthy controls: A high-density surface EMG investigation. Gallina A, Pollock CL, Vieira TM, Ivanova TD, Garland SJ. Gait Posture. 2016 Feb;44:103-9
Between-day reliability of triceps surae responses to standing perturbations in people post-stroke and healthy controls: A high-density surface EMG investigation.
Abstract
The reliability of triceps surae electromyographic responses to standing perturbations in people after stroke and healthy controls is unknown. High-Density surface Electromyography (HDsEMG) is a technique that records electromyographic signals from different locations over a muscle, overcoming limitations of traditional surface EMG such as between-day differences in electrode placement. In this study, HDsEMG was used to measure responses from soleus (SOL, 18 channels) and medial and lateral gastrocnemius (MG and LG, 16 channels each) in 10 people after stroke and 10 controls. Timing and amplitude of the response were estimated for each channel of the grids. Intraclass Correlation Coefficient (ICC) and normalized Standard Error of Measurement (SEM%) were calculated for each channel individually (single-channel configuration) and on the median of each grid (all-channels configuration). Both timing (single-channel: ICC=0.75-0.96, SEM%=5.0-9.1; all-channels: ICC=0.85-0.97; SEM%=3.5-6.2%) and amplitude (single-channel: ICC=0.60-0.91, SEM%=25.1-46.6; ICC=0.73-0.95, SEM%=19.3-42.1) showed good-to-excellent reliability. HDsEMG provides reliable estimates of EMG responses to perturbations both in individuals after stroke and in healthy controls; reliability was marginally better for the all-channels compared to the single-channel configuration.
Copyright © 2015 Elsevier B.V. All rights reserved.
KEYWORDS:
High-density surface electromyography; Perturbation; Posture; Reliability; Stroke
- PMID:
- 27004641
- DOI:
- 10.1016/j.gaitpost.2015.11.015
Electrode position markedly affects knee torque in tetanic, stimulated contractions. Vieira TM, Potenza P, Gastaldi L, Botter A. Eur J Appl Physiol. 2016 Feb;116(2):335-42
Electrode position markedly affects knee torque in tetanic, stimulated contractions.
Author information
- 1
- Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.
- 2
- Departamento de Arte Corporal, Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio De Janeiro, Brazil.
- 3
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Politecnico di Torino, Torino, Italy.
- 4
- Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy. alberto.botter@polito.it.
Abstract
PURPOSE:
The purpose of this study was to investigate how much the distance between stimulation electrodes affects the knee extension torque in tetanic, electrically elicited contractions.
METHODS:
Current pulses of progressively larger amplitude, from 0 mA to maximally tolerated intensities, were delivered at 20 pps to the vastus medialis, rectus femoris and vastus lateralis muscles of ten, healthy male subjects. Four inter-electrode distances were tested: 32.5% (L1), 45.0% (L2), 57.5% (L3) and 70% (L4) of the distance between the patella apex and the anterior superior iliac spine. The maximal knee extension torque and the current leading to the maximal torque were measured and compared between electrode configurations.
RESULTS:
The maximal current tolerated by each participant ranged from 60 to 100 mA and did not depend on the inter-electrode distance. The maximal knee extension torque elicited did not differ between L3 and L4 (P = 0.15) but, for both conditions, knee torque was significantly greater than for L1 and L2 (P < 0.024). On average, the extension torque elicited for L3 and L4 was two to three times greater than that obtained for L1 and L2. The current leading to maximal torque was not as sensitive to inter-electrode distance. Except for L1 current intensity did not change with electrode configuration (P > 0.16).
CONCLUSIONS:
Key results presented here revealed that for a given stimulation intensity, knee extension torque increased dramatically with the distance between electrodes. The distance between electrodes seems therefore to critically affect knee torque, with potential implication for optimising exercise protocols based on electrical stimulation.
KEYWORDS:
Electrode configuration; Functional electrical stimulation; Quadriceps muscle; Stimulation parameters
- PMID:
- 26526290
- DOI:
- 10.1007/s00421-015-3289-3
The correct episiotomy: Does it exist? Merletti R, Riva D, Cescon C, Zacesta V. Int Urogynecol J. 2016 Jan;27(1):161-2. doi: 10.1007/s00192-015-2879-2. Epub 2015 Nov 12.
Electrode position markedly affects knee torque in tetanic, stimulated contractions.
Author information
- 1
- Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.
- 2
- Departamento de Arte Corporal, Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio De Janeiro, Brazil.
- 3
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Politecnico di Torino, Torino, Italy.
- 4
- Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy. alberto.botter@polito.it.
Abstract
PURPOSE:
The purpose of this study was to investigate how much the distance between stimulation electrodes affects the knee extension torque in tetanic, electrically elicited contractions.
METHODS:
Current pulses of progressively larger amplitude, from 0 mA to maximally tolerated intensities, were delivered at 20 pps to the vastus medialis, rectus femoris and vastus lateralis muscles of ten, healthy male subjects. Four inter-electrode distances were tested: 32.5% (L1), 45.0% (L2), 57.5% (L3) and 70% (L4) of the distance between the patella apex and the anterior superior iliac spine. The maximal knee extension torque and the current leading to the maximal torque were measured and compared between electrode configurations.
RESULTS:
The maximal current tolerated by each participant ranged from 60 to 100 mA and did not depend on the inter-electrode distance. The maximal knee extension torque elicited did not differ between L3 and L4 (P = 0.15) but, for both conditions, knee torque was significantly greater than for L1 and L2 (P < 0.024). On average, the extension torque elicited for L3 and L4 was two to three times greater than that obtained for L1 and L2. The current leading to maximal torque was not as sensitive to inter-electrode distance. Except for L1 current intensity did not change with electrode configuration (P > 0.16).
CONCLUSIONS:
Key results presented here revealed that for a given stimulation intensity, knee extension torque increased dramatically with the distance between electrodes. The distance between electrodes seems therefore to critically affect knee torque, with potential implication for optimising exercise protocols based on electrical stimulation.
KEYWORDS:
Electrode configuration; Functional electrical stimulation; Quadriceps muscle; Stimulation parameters
- PMID:
- 26526290
- DOI:
- 10.1007/s00421-015-3289-3
2011-2015
. Territory and fiber orientation of vastus medialis motor units: A Surface electromyography investigation. Gallina A, Vieira T. Muscle Nerve. 2015 Dec;52(6):1057-65. doi: 10.1002/mus.24662. Epub 2015 Sep 8.
Territory and fiber orientation of vastus medialis motor units: A Surface electromyography investigation.
Author information
- 1
- Laboratorio per l’Ingegneria del Sistema Nuromuscolare, Dipartimento di Ingegneria Elettronica, Politecnico di Torino, Via Cavalli 22/h, 10138, Torino, Italy.
- 2
- Graduate Program in Rehabilitation Sciences, Department of Physical Therapy, University of British Columbia, Vancouver (BC), Canada.
- 3
- Escola de Educação Física e Desportos, Departamento de Arte Corporal, Universidade Federal do Rio de Janeiro, Rio di Janeiro, Brazil.
Abstract
INTRODUCTION:
The aim of this study was to determine whether muscle fibers innervated by single motor neurons are confined in small subvolumes of the vastus medialis (VM) and if motor unit fiber orientation depends on their position within the muscle.
METHODS:
Single motor units were identified from a grid of surface electrodes. The size of their surface representation and fiber orientation were extracted using an algorithm validated on simulated signals.
RESULTS:
The action potentials of 77 motor units were represented locally on the skin (10th-90th percentiles: 14-25 mm). According to simulations, this indicates territories smaller than 11.8-64.8 mm. Motor units in distal regions of VM had fibers at a greater angle than those in proximal regions (R = -0.54, P < 0.001).
CONCLUSION:
Motor units with small territories and varying fiber orientations may be an anatomical predisposition to regulate how regions within VM apply forces to the patella. This could help to redistribute loads within the joint in painful conditions.
© 2015 Wiley Periodicals, Inc.
KEYWORDS:
compartmentalization; electromyography; motor unit; quadriceps; surface EMG; territory
- PMID:
- 25808985
- DOI:
- 10.1002/mus.24662
Filtered Virtual Reference: A New Method for the Reduction of Power Line Interference With Minimal Distortion of Monopolar Surface EMG. Botter A, Vieira TM. IEEE Trans Biomed Eng. 2015 Nov;62(11):2638-47. doi: 10.1109/TBME.2015.2438335.
Filtered Virtual Reference: A New Method for the Reduction of Power Line Interference With Minimal Distortion of Monopolar Surface EMG.
Abstract
GOAL:
This study tests and validates a new method to remove power line interference from monopolar EMGs detected by multichannel systems: the filtered virtual reference (FVR). FVR is an adaptation of the virtual reference (VR) method, which consists in referencing signals detected by each electrode in a grid to their spatial average. Signals may however be distorted with the VR approach, in particular when the skin region where the detection system is positioned does not cover the entire muscle.
METHODS:
Simulated and experimental EMGs were used to compare the performance of FVR and VR in terms of interference reduction and distortion of monopolar signals referred to a remote reference.
RESULTS:
Simulated data revealed the monopolar EMG signals processed with FVR were significantly less distorted than those filtered by VR. These results were similarly observed for experimental signals. Moreover, FVR method outperformed VR in removing power line interference when it was distributed unevenly across the signals of the grid.
CONCLUSION:
Key results demonstrated that FVR improves the VR method as it reduces interference while preserving the information content of monopolar signals.
SIGNIFICANCE:
Although the actual distribution of motor unit action potential is represented in monopolar EMGs, collecting high quality monopolar signals is challenging. This study presents a possible solution to this issue; FVR provides undistorted monopolar signals with negligible interference and is insensitive to muscle architecture. It is therefore relevant for EMG applications benefiting from a clean monopolar detection (e.g., decomposition, control of prosthetic devices, motor unit number estimation).
- PMID:
- 26513767
- DOI:
- 10.1109/TBME.2015.2438335
Spatial variability in cortex-muscle coherence investigated with magnetoencephalography and high-density surface electromyography. Piitulainen H, Botter A, Bourguignon M, Jousmäki V, Hari R. J Neurophysiol. 2015 Nov;114(5):2843-53. doi: 10.1152/jn.00574.2015. Epub 2015 Sep 9.
Spatial variability in cortex-muscle coherence investigated with magnetoencephalography and high-density surface electromyography.
Author information
- 1
- Brain Research Unit, Department of Neuroscience and Biomedical Engineering, and MEG Core and Advanced Magnetic Imaging (AMI) Centre, Aalto NeuroImaging, Aalto University School of Science, Aalto, Espoo, Finland; and harri.piitulainen@aalto.fi.
- 2
- Laboratory of Engineering of Neuromuscular System and Motor Rehabilitation, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Turin, Italy.
- 3
- Brain Research Unit, Department of Neuroscience and Biomedical Engineering, and MEG Core and Advanced Magnetic Imaging (AMI) Centre, Aalto NeuroImaging, Aalto University School of Science, Aalto, Espoo, Finland; and.
Abstract
Cortex-muscle coherence (CMC) reflects coupling between magnetoencephalography (MEG) and surface electromyography (sEMG), being strongest during isometric contraction but absent, for unknown reasons, in some individuals. We used a novel nonmagnetic high-density sEMG (HD-sEMG) electrode grid (36 mm × 12 mm; 60 electrodes separated by 3 mm) to study effects of sEMG recording site, electrode derivation, and rectification on the strength of CMC. Monopolar sEMG from right thenar and 306-channel whole-scalp MEG were recorded from 14 subjects during 4-min isometric thumb abduction. CMC was computed for 60 monopolar, 55 bipolar, and 32 Laplacian HD-sEMG derivations, and two derivations were computed to mimic “macroscopic” monopolar and bipolar sEMG (electrode diameter 9 mm; interelectrode distance 21 mm). With unrectified sEMG, 12 subjects showed statistically significant CMC in 91-95% of the HD-sEMG channels, with maximum coherence at ∼25 Hz. CMC was about a fifth stronger for monopolar than bipolar and Laplacian derivations. Monopolar derivations resulted in most uniform CMC distributions across the thenar and in tightest cortical source clusters in the left rolandic hand area. CMC was 19-27% stronger for HD-sEMG than for “macroscopic” monopolar or bipolar derivations. EMG rectification reduced the CMC peak by a quarter, resulted in a more uniformly distributed CMC across the thenar, and provided more tightly clustered cortical sources than unrectifed sEMGs. Moreover, it revealed CMC at ∼12 Hz. We conclude that HD-sEMG, especially with monopolar derivation, can facilitate detection of CMC and that individual muscle anatomy cannot explain the high interindividual CMC variability.
Copyright © 2015 the American Physiological Society.
KEYWORDS:
corticomuscular coherence; magnetoencephalography; multichannel EMG; sensorimotor cortex; spatial filter
- PMID:
- 26354317
- PMCID:
- PMC4737422
- DOI:
- 10.1152/jn.00574.2015
Spatial variation of compound muscle action potentials across human gastrocnemius medialis. Vieira TM, Botter A, Minetto MA, Hodson-Tole EF. J Neurophysiol. 2015 Sep;114(3):1617-27. doi: 10.1152/jn.00221.2015. Epub 2015 Jul 8.
Spatial variation of compound muscle action potentials across human gastrocnemius medialis.
Abstract
The massed action potential (M wave) elicited through nerve stimulation underpins a wide range of physiological and mechanical understanding of skeletal muscle structure and function. Although systematic approaches have evaluated the effect of different factors on M waves, the effect of the location and distribution of activated fibers within the muscle remains unknown. By detecting M waves from the medial gastrocnemius (MG) of 12 participants with a grid of 128 electrodes, we investigated whether different populations of muscle units have different spatial organization within MG. If populations of muscle units occupy discrete MG regions, current pulses of progressively greater intensities applied to the MG nerve branch would be expected to lead to local changes in M-wave amplitudes. Electrical pulses were therefore delivered at 2 pps, with the current pulse amplitude increased every 10 stimuli to elicit different degrees of muscle activation. The localization of MG response to increases in current intensity was determined from the spatial distribution of M-wave amplitude. Key results revealed that increases in M-wave amplitude were detected somewhat locally, by 10-50% of the 128 electrodes. Most importantly, the electrodes detecting greatest increases in M-wave amplitude were localized at different regions in the grid, with a tendency for greater stimulation intensities to elicit M waves in the more distal MG region. The presented results indicate that M waves recorded locally may not provide a representative MG response, with major implications for the estimation of, e.g., the maximal stimulation levels, the number of motor units, and the onset and normalization in H-reflex studies.
Copyright © 2015 the American Physiological Society.
KEYWORDS:
M wave; electrical stimulation; medial gastrocnemius; motor units; surface EMG
- PMID:
- 26156382
- PMCID:
- PMC4563026
- DOI:
- 10.1152/jn.00221.2015
Examination of Poststroke Alteration in Motor Unit Firing Behavior Using High-Density Surface EMG Decomposition. Li X, Holobar A, Gazzoni M, Merletti R, Rymer WZ, Zhou P. IEEE Trans Biomed Eng. 2015 May;62(5):1242-52. doi: 10.1109/TBME.2014.2368514. Epub 2014 Nov 7.
Examination of Poststroke Alteration in Motor Unit Firing Behavior Using High-Density Surface EMG Decomposition.
Abstract
Recent advances in high-density surface electromyogram (EMG) decomposition have made it a feasible task to discriminate single motor unit activity from surface EMG interference patterns, thus providing a noninvasive approach for examination of motor unit control properties. In the current study, we applied high-density surface EMG recording and decomposition techniques to assess motor unit firing behavior alterations poststroke. Surface EMG signals were collected using a 64-channel 2-D electrode array from the paretic and contralateral first dorsal interosseous (FDI) muscles of nine hemiparetic stroke subjects at different isometric discrete contraction levels between 2 to 10 N with a 2 N increment step. Motor unit firing rates were extracted through decomposition of the high-density surface EMG signals and compared between paretic and contralateral muscles. Across the nine tested subjects, paretic FDI muscles showed decreased motor unit firing rates compared with contralateral muscles at different contraction levels. Regression analysis indicated a linear relation between the mean motor unit firing rate and the muscle contraction level for both paretic and contralateral muscles (p < 0.001), with the former demonstrating a lower increment rate (0.32 pulses per second (pps)/N) compared with the latter (0.67 pps/N). The coefficient of variation (averaged over the contraction levels) of the motor unit firing rates for the paretic muscles (0.21 ± 0.012) was significantly higher than for the contralateral muscles (0.17 ± 0.014) (p < 0.05). This study provides direct evidence of motor unit firing behavior alterations poststroke using surface EMG, which can be an important factor contributing to hemiparetic muscle weakness.
- PMID:
- 25389239
- PMCID:
- PMC4406795
- DOI:
- 10.1109/TBME.2014.2368514
Variations in the spatial distribution of the amplitude of surface electromyograms are unlikely explained by changes in the length of medial gastrocnemius fibres with knee joint angle. Avancini C, de Oliveira LF, Menegaldo LL, Vieira TM. PLoS One. 2015 May 22;10(5):e0126888. doi: 10.1371/journal.pone.0126888. eCollection 2015
Variations in the spatial distribution of the amplitude of surface electromyograms are unlikely explained by changes in the length of medial gastrocnemius fibres with knee joint angle.
Author information
- 1
- Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil.
- 2
- Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil; Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil.
- 3
- Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil; Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Politecnico di Torino, Torino, TO, Italia.
Abstract
This study investigates whether knee position affects the amplitude distribution of surface electromyogram (EMG) in the medial gastrocnemius (MG) muscle. Of further concern is understanding whether knee-induced changes in EMG amplitude distribution are associated with regional changes in MG fibre length. Fifteen surface EMGs were acquired proximo-distally from the MG muscle while 22 (13 male) healthy participants (age range: 23-47 years) exerted isometric plantar flexion at 60% of their maximal effort, with knee fully extended and at 90 degrees flexion. The number of channels providing EMGs with greatest amplitude, their relative proximo-distal position and the EMG amplitude averaged over channels were considered to characterise changes in myoelectric activity with knee position. From ultrasound images, collected at rest, fibre length, pennation angle and fat thickness were computed for MG proximo-distal regions. Surface EMGs detected with knee flexed were on average five times smaller than those collected during knee extended. However, during knee flexed, relatively larger EMGs were detected by a dramatically greater number of channels, centred at the MG more proximal regions. Variation in knee position at rest did not affect the proximo-distal values obtained for MG fibre length, pennation angle and fat thickness. Our main findings revealed that, with knee flexion: i) there is a redistribution of activity within the whole MG muscle; ii) EMGs detected locally unlikely suffice to characterise the changes in the neural drive to MG during isometric contractions at knee fully extended and 90 degrees flexed positions; iii) sources other than fibre length may substantially contribute to determining the net, MG activation.
- PMID:
- 26001107
- PMCID:
- PMC4441502
- DOI:
- 10.1371/journal.pone.0126888
The effect of lymph drainage on the myoelectric manifestation of vastus lateralis fatigue: Preliminary results. Vieira TM, Readi NG, Schwarcke L, Botter A. Conf Proc IEEE Eng Med Biol Soc. 2015;2015:6671-4. doi: 10.1109/EMBC.2015.7319923.
The effect of lymph drainage on the myoelectric manifestation of vastus lateralis fatigue: Preliminary results.
Abstract
Variations in surface electromyograms (EMGs) collected from the vastus lateralis muscle during isometric fatiguing contractions were investigated pre-post lymphatic drainage (intervention group, N=3) and pre-post rest (control group, N=3). The slope of conduction velocity and of EMG amplitude and spectral descriptors was computed from the start to the failure time; the instant after which subjects could not endure contractions. When compared to subjects in the control group, those in the intervention group endured longer. Similarly, muscle fatigue affected to a lesser extent EMGs following lymphatic drainage than following rest. These preliminary results suggest the lymphatic drainage may potentially delay muscle fatigue.
- PMID:
- 26737823
- DOI:
- 10.1109/EMBC.2015.7319923
High Density EMG investigation of H-reflex distribution over the soleus muscle. Botter A, Vazzoler I, Vieira TM. Conf Proc IEEE Eng Med Biol Soc. 2015 Aug;2015:3460-3. doi: 10.1109/EMBC.2015.7319137
High Density EMG investigation of H-reflex distribution over the soleus muscle.
Abstract
The spatial distribution of H-reflexes over soleus muscle was investigated through High-Density EMG in five healthy subjects. The posterior tibial nerve was stimulated with a staircase current envelope with 1mA steps. The regions where the incremental responses (incremental H-reflexes) occurred were identified for each stimulation step with a validated segmentation algorithm. The average centroid of the segmented areas was located over the Achilles tendon, 5 cm below the myo-tendinous junction of the medial gastrocnemius. The average dimension of these regions corresponded to 28% of the surface covered by the grid of electrodes. The amplitude of H-reflexes recorded in the segmented areas was higher than the average amplitude computed over the entire detection system as well as the H-reflex recorded by the electrode positioned according to SENIAM guidelines. These preliminary results suggest that: i) H-reflex detected from a specific soleus region unlikely reflects the whole muscle volume and ii) H-reflexes with greatest amplitude can be recorded over the Achilles tendon.
- PMID:
- 26737037
- DOI:
- 10.1109/EMBC.2015.7319137
Power line interference attenuation in multi-channel sEMG signals: Algorithms and analysis. Soedirdjo SD, Ullah K, Merletti R. Conf Proc IEEE Eng Med Biol Soc. 2015 Aug;2015:3823-6. doi: 10.1109/EMBC.2015.7319227.
Power line interference attenuation in multi-channel sEMG signals: Algorithms and analysis.
Abstract
Electromyogram (EMG) recordings are often corrupted by power line interference (PLI) even though the skin is prepared and well-designed instruments are used. This study focuses on the analysis of some of the recent and classical existing digital signal processing approaches have been used to attenuate, if not eliminate, the power line interference from EMG signals. A comparison of the signal to interference ratio (SIR) of the output signals is presented, for four methods: classical notch filter, spectral interpolation, adaptive noise canceller with phase locked loop (ANC-PLL) and adaptive filter, applied to simulated multichannel monopolar EMG signals with different SIR. The effect of each method on the shape of the EMG signals is also analyzed. The results show that ANC-PLL method gives the best output SIR and lowest shape distortion compared to the other methods. Classical notch filtering is the simplest method but some information might be lost as it removes both the interference and the EMG signals. Thus, it is obvious that notch filter has the lowest performance and it introduces distortion into the resulting signals.
- PMID:
- 26737127
- DOI:
- 10.1109/EMBC.2015.7319227
Modulation of tibialis anterior muscle activity changes with upright stance width. Lemos T, Imbiriba LA, Vargas CD, Vieira TM. J Electromyogr Kinesiol. 2015 Feb;25(1):168-74. doi: 10.1016/j.jelekin.2014.07.009. Epub 2014 Aug 8.
Modulation of tibialis anterior muscle activity changes with upright stance width.
Author information
- 1
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, RJ, Brazil. Electronic address: lemoscarvalho.thiago@gmail.com.
- 2
- Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, RJ, Brazil.
- 3
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, RJ, Brazil.
- 4
- Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, RJ, Brazil; Laboratorio di Ingegneria del Sistema Neuromuscolare, Politecnico di Torino, Torino, Italy.
Abstract
When individuals stand with their feet apart, activation of tibialis anterior (TA) muscle seems to slightly exceed rest levels. In narrow stances, conversely, the stabilization of body lateral sways may impose marked, active demand on ankle inversors/eversors. In this study we investigate how much the modulation in TA activity, associated to center of pressure (COP) lateral sways, changes when stance width reduces. Surface EMG and COP coordinates were collected from 17 subjects at three different stances: feet apart, feet together and tandem. Pearson correlation analysis was applied to check whether the expected greater modulations in TA activity corresponded to a stronger association between fluctuations in EMG amplitude and COP lateral sways. When standing at progressively narrower stances participants showed larger fluctuations in COP lateral sways (p<0.01) and higher EMG-COP association (p<0.01); marked increases in TA activity were only observed in tandem stance (p<0.001). Interestingly, more pronounced modulations in TA activity were observed for subjects showing greater association between EMG amplitude and COP sways in feet together and tandem stance (Pearson R>0.56, p<0.02), though not when standing with feet apart (R=-0.22, p=0.40). These results indicate that the contribution of TA activity to lateral sway control increases for narrower stances.
Copyright © 2014 Elsevier Ltd. All rights reserved.
KEYWORDS:
Posture control; Stance width; Surface EMG; Tibialis anterior
- PMID:
- 25156446
- DOI:
- 10.1016/j.jelekin.2014.07.009