Multichannel Electromyography Research Articles

Experimental muscle pain changes the spatial distribution of upper trapezius muscle activity during sustained contraction

Objective To investigate the effect of local excitation of nociceptive muscle afferents on the spatial distribution of muscle activity. Methods Surface electromyographic (EMG) signals were recorded from the upper trapezius muscle of 10 healthy volunteers with a 5 × 13 electrode grid during 90-s isometric contractions before, during, 15 and 30 min after intramuscular injection of hypertonic (painful) or isotonic (non-painful) saline. From the multi-channel EMG recordings, two-dimensional maps of root mean square and mean power frequency were obtained. The centre of gravity of the root mean square map was used to quantify global changes in the spatial distribution of muscle activity. Results During sustained contractions, average root mean square increased, average mean frequency decreased and the centre of gravity moved cranially. During experimental muscle pain, compared to before injection, the average root mean square decreased and there was a caudal shift of the centre of gravity. Fifteen minutes after the painful injection the centre of gravity returned to its original position. Conclusions Short-term dynamic reorganization of the spatial distribution of muscle activity occurred in response to nociceptive afferent input. Significance The study furnishes an extension of the pain adaptation model indicating heterogeneous inhibition of muscle activity.

Behaviour of motor unit action potential rate, estimated from surface EMG, as a measure of muscle activation level

BackgroundSurface electromyography (EMG) parameters such as root-mean-square value (RMS) are commonly used to assess the muscle activation level that is imposed by the central nervous system (CNS). However, RMS is influenced not only by motor control aspects, but also by peripheral properties of the muscle and recording setup. To assess motor control separately, the number of motor unit action potentials (MUAPs) per second, or MUAP Rate (MR) is a potentially useful measure. MR is the sum of the firing rates of the contributing MUs and as such reflects the two parameters that the CNS uses for motor control: number of MUs and firing rate.MR can be estimated from multi-channel surface EMG recordings. The objective of this study was to explore the behaviour of estimated MR (eMR) in relation to number of active MUs and firing rate. Furthermore, the influence of parameters related to peripheral muscle properties and recording setup (number of fibers per MU, fiber diameter, thickness of the subcutaneous layer, signal-to-noise-ratio) on eMR was compared with their influence on RMS.MethodsPhysiological parameters were varied in a simulation model that generated multi-channel EMG signals. The behaviour of eMR in simulated conditions was compared with its behaviour in experimental conditions. Experimental data was obtained from the upper trapezius muscle during a shoulder elevation task (20–100 N).ResultsThe simulations showed strong, monotonously increasing relations between eMR and number of active MUs and firing rate (r2 > 0.95). Because of unrecognized superimpositions of MUAPs, eMR was substantially lower than the actual MUAP Rate (aMR). The percentage of detected MUAPs decreased with aMR, but the relation between eMR and aMR was rather stable in all simulated conditions. In contrast to RMS, eMR was not affected by number of fibers per MU, fiber diameter and thickness of the subcutaneous layer. Experimental data showed a strong relation between eMR and force (individual second order polynomial regression: 0.96 < r2 < 0.99).ConclusionAlthough the actual number of MUAPs in the signal cannot be accurately extracted with the present method, the stability of the relation between eMR and aMR and its independence of muscle properties make eMR a suitable parameter to assess the input from the CNS to the muscle at low contraction levels non-invasively.

Impaired Viscerosomatic Reflexes and Abdominal-Wall Dystony Associated With Bloating

Abdominal bloating is a frequent complaint in irritable bowel syndrome (IBS), but its underlying mechanism remains uncertain. Our aim was to determine whether the abdominal wall, specifically its adaptation to intra-abdominal volumes, plays a role. In 12 patients complaining of abdominal bloating (8 IBS and 4 functional bloating) and in 12 healthy controls, the effect of colonic gas load (24 mL/min rectal gas infusion for 1 hour) on perception (measured by a 0-6 scale), abdominal girth, and muscular activity was tested. With the participants sitting on an ergonomic chair and the trunk erect, multichannel electromyography was measured via bipolar surface electrodes located over the upper and lower rectus abdominis, and the external and internal oblique bilaterally. In healthy controls, colonic gas loads produced subjective symptoms (score, 3.0 +/- 0.3), objective abdominal distention (girth increment, 6 +/- 1 mm), and increased the activity of the abdominal muscles (external oblique activity, 11% +/- 3% in; P < .05 vs basal). At the same infused gas volumes, the patients developed significantly more symptoms (score, 4.5 +/- 0.4) and abdominal distention (11 +/- 1 mm; P < .05 vs healthy for both). These abnormal responses were associated with failed tonic contraction of the abdominal wall (external oblique activity change, -1% +/- 4%; P value not significant vs basal) and paradoxic relaxation of the internal oblique (activity reduction, 26% +/- 7%; P < .01 vs basal). In patients with bloating, abdominal perception and distention in response to intra-abdominal volume increments are exaggerated markedly and associated with muscular dystony of the abdominal wall.

Non-invasive Assessment of the Gracilis Muscle by Means of Surface Electromyography Electrode Arrays

The purpose of the study was the non-invasive investigation of the innervation zone (IZ) location of the gracilis muscle of both thighs by means of surface electromyography (EMG). Multichannel EMG signals were detected by means of a flexible array of 16 equally spaced silver bar electrodes. Tests were performed on both gracilis muscles on 15 subjects. Motor unit (MU) action potentials were visually identified and extracted. The locations of the IZs of the recognized MUs were statistically analyzed to find significant differences between the subjects and between the right and left muscle of each subject. A statistically significant difference was found between the gracilis IZ position in the two sides, with more proximal IZs on the left side. This difference suggests a possible role of surface EMG in preoperative evaluation of patients prepared for the dynamic graciloplasty procedure. This test would provide an objective criterion for the choice of the gracilis muscle to be transposed with the highest probability of success.

Spinal Myoclonus After Spinal Cord Injury

Background/Objective: In the course of examining spinal motor function in many hundreds of people with traumatic spinal cord injury, we encountered 6 individuals who developed involuntary and rhythmic contractions in muscles of their legs. Although there are many reports of unusual muscle activation patterns associated with different forms of myoclonus, we believe that certain aspects of the patterns seen with these 6 subjects have not been previously reported. These patterns share many features with those associated with a spinal central pattern generator for walking.Methods: Subjects in this case series had a history of chronic injury to the cervical spinal cord, resulting in either complete (ASIA A; n = 4) or incomplete (ASIA D; n = 2) quadriplegia. We used multi-channel electromyography recordings of trunk and leg muscles of each subject to document muscle activation patterns associated with different postures and as influenced by a variety of sensory stimuli.Results: Involuntary contractions spanned multiple leg muscles bilaterally, sometimes including weak abdominal contractions. Contractions were smooth and graded and were highly reproducible in rate for a given subject (contraction rates were 0.3-0.5 Hz). These movements did not resemble the brief rapid contractions (ie, "jerks") ascribed to some forms of spinal myoclonus. For all subjects, the onset of involuntary muscle contraction was dependent upon hip angle; contractions did not occur unless the hips (and knees) were extended (ie, subjects were supine). In the 4 ASIA A subjects, contractions occurred simultaneously in all muscles (agonists and antagonists) bilaterally. In sharp contrast, contractions in the 2 ASIA D subjects were reciprocal between agonists and antagonists within a limb and alternated between limbs, such that movements in these 2 subjects looked just like repetitive stepping. Finally, each of the 6 subjects had a distinct pathology of their spinal cord, nerve roots, distal trunk, or thigh; in 4 of these subjects, treatment of the pathology eliminated the involuntary movements.Conclusion: The timing, distribution, and reliance upon hip angle suggest that these movement patterns reflect some elements of a central pattern generator for stepping. Emergence of these movements in persons with chronic spinal cord injury is extremely rare and appears to depend upon a combination of the more rostrally placed injury and a pathologic process leading to a further enhancement of excitability in the caudal spinal cord.

Motor unit action potential topography and its use in motor unit number estimation

High-density multichannel electromyography (EMG) recordings add spatial information to the temporal information content of the surface EMG (sEMG) signal. This study explores the potential value of such multichannel information at a single motor unit level, in particular for the improvement of motor unit number estimation (MUNE) techniques. It is shown that multichannel recordings make it easier to distinguish motor unit action potentials (MUAPs) and that MUAP combinations can be better resolved. Furthermore, the spatiotemporal information allows a quantitative assessment of the representativity of the mean of the recorded MUAPs in relation to the maximum CMAP, i.e., for the muscle as a whole. In general, this is practically impossible on the basis of temporal information alone. For these reasons, we expect that high-density sEMG has the potential to address several methodological limitations of single channel surface EMG recordings. This is specifically illustrated in this study for one of the MUNE techniques in use, the F-response method.

The Role of Intraoperative Electromyographic Monitoring in Lumbosacral Lipomas

To demonstrate the role of intraoperative multichannel electromyographic (EMG) monitoring to reduce postoperative deterioration and achieve full untethering of complex occult dysraphisms. A retrospective analysis was performed on 66 patients who underwent operation for lumbosacral lipomas. Twenty recent cases were submitted to EMG monitoring and stimulation. All patients presented symptoms at the time of surgery, and 74% exhibited progressive deterioration during the lengthy preoperative period. Postoperative surgery-related deterioration was observed in 6% of patients. This number was reduced to zero with the introduction of intraoperative EMG monitoring. Intraoperative multichannel EMG monitoring can be carried out and requires only minimal changes to anesthetic procedures. With this method, it is possible to better identify the neural structures of complex malformations, reducing the risks of surgical damage and incomplete detethering.

Comparison of the electromyographic activity in the upper trapezius and biceps brachii muscle in subjects with muscular disorders: a pilot study

The aim of the present study was to investigate the extent to which work-related muscular disorders of the upper trapezius affect the activity of other pain-free muscles, in particular in the biceps brachii. Two groups of female subjects (age >43 years) participated in the study: seven affected subjects with self-reported disorders in the shoulder/neck region (cases) and nine healthy subjects (control group). Multi-channel electromyography (EMG) and force were recorded during maximum voluntary contractions (MVC) and during 6 min sustained contractions (at 30% MVC) of the upper trapezius and biceps brachii on the dominant side. From the EMG signals, the root mean square (RMS), median frequency (MDF) and single motor unit (MU) conduction velocity (CV) were estimated. From the force signal, the coefficient of variation was calculated. All data are presented as mean values and standard deviation. Differences between the cases and controls were found in the MVC force of the upper trapezius, which was lower in cases [253 (70) N] than in controls [357 (75) N], while the coefficient of variation of force during the sustained contraction was increased [cases 5.5 (2.2); controls 4.1 (1.9)]. The RMS (normalized to the RMS at MVC) during the 6 min sustained contractions was significantly lower in the cases than in the controls for both the upper trapezius and the biceps brachii. A tendency towards a smaller increase in the RMS with fatigue was only found in the trapezius muscle [slope: cases 6.5 (14.1) %/min, controls 10.2 (12.9) %/min]. No differences were found between the two subject groups with respect to the MDF and single MU CV in both muscles. While the lower RMS for the trapezius muscles of the cases may reflect changes at the local level, as well as in motor control, the lower biceps activity indicates a change in the central control strategies of the primarily unaffected muscle. Indications for a changed fatigability of the muscle were only found in the trapezius.

Multivariate AR modeling of electromyography for the classification of upper arm movements

Objective We compared the performance of two feature extraction methods for multichannel electromyography (EMG) based arm movement classification. One method was to use a scalar autoregressive model (sAR) for each channel. Another was to model all channels as a whole by a multivariate AR model (mAR). Methods The classified arm movements included elbow flexion, elbow extension, forearm pronation and internal shoulder rotation. Six-channel bipolar EMG signals were collected from four electrodes fixed on the biceps, triceps, brachioradialis and deltoid. Fifteen two-channel and four three-channel configurations were formed out of these six-channel signals for a comparison of different channel combinations. Leave-one-out cross-validation was adopted for evaluating the classification performance using a parametric statistical classifier. Results We processed a total of 216 EMG segments obtained from repeated 18 performances by three normal subjects. mAR model based feature set achieved a better classification accuracy than sAR did for each configuration. Moreover, significance of improvement was greater than 0.95 for those configurations which consisted of EMG channels that were close spatially. Conclusions The stronger the cross-correlation among EMG channels the more improvement of classification accuracy one would expect from using a mAR model.

Work physiology and ergonomics in Germany: From the past to future challenges

Fundamental knowledge of anthropometric dimensions and biomechanical properties, of the capacities, as well as limitations, of the human sensory organs and the hand-arm system, i.e., comprehensive work-physiological knowledge of the characteristics of the human organism, always was, and will still in the future remain, a prerequisite for the truly ergonomic design of workplaces and work tools. Especially in Germany, work physiology represents the nucleus of today's work science or ergonomics. Besides the tasks and objectives of work physiology in ergonomics education, the principles of work-physiological research approaches are described. When evaluating workplaces and work tools, measuring physiological cost which the organism or the organs have to pay must be quantified. Similar to heart rate increases above the resting level associated with whole-body dynamic muscle work, the physiological cost of the muscles involved in repetitive manual movements, and the operating of hand-held tools or computer input devices can be measured via multi-channel electromyography. Physiological costs of sound exposures can be quantified in temporary hearing threshold shifts and their restitution, and physiological cost to the eyes is represented, for example, in varying levels of accommodation, adaptation, and fixation. Thinking in terms of physiological cost of work guarantees safe guidance in order to achieve human-oriented working conditions. According to recent developments in acts, ordinances, directions, and regulations in Europe, ergonomics has gained a high rank, but successful ergonomic interactions depend on comprehensive knowledge and experience, and require core competency in work-physiology as well as in ergonomics work design.

Surface EMG crosstalk between knee extensor muscles: experimental and model results.

Surface electromyographic (EMG) crosstalk between vastus lateralis, vastus medialis, and rectus femoris muscles was evaluated by selective electrical stimulation of one muscle and recording from the stimulated and another muscle with linear surface arrays of eight electrodes. The ratio between the amplitude of the signals recorded over nonstimulated and stimulated muscles and their correlation coefficient were used as indices to quantify crosstalk. Single-differential and double-differential detection systems were used with interelectrode distances in the range 10-40 mm. The multichannel EMG signals clearly showed that crosstalk is largely due to nonpropagating potentials that correspond in time to the end of the propagation of the action potentials generated by the stimulated muscle. The crosstalk signal increased with increasing interelectrode distance and was statistically higher for single- than for double-differential recordings. The correlation-based indices of crosstalk were poorly correlated with the amplitude-based indices. Moreover, the characteristic spectral frequencies of the signals detected over the nonstimulated muscles were statistically higher than those from the stimulated muscles. A mathematical model of signal generation was used to explain the experimental findings. This study clarifies many controversial findings of past investigations and creates the basis for crosstalk interpretation, simulation, and reduction.

Cortical activation related to arm-movement combinations.

Recent studies support the long-standing hypothesis that continuous arm movements consist of overlapping, discrete submovements. However, the cortical activation associated with these submovements is unclear. We tested the hypothesis that electroencephalography (EEG) activity would more strongly correspond to the particular combinations of muscle electrical activity, the independent components (ICs) of surface electromyography (EMG), than the surface EMG from individual muscles alone. We examined data recorded from two normal subjects performing sustained submaximal contractions or continual, unpaced repetitive movements of the arm. Independent component analysis (ICA) was used to determine the ICs of the multichannel EMG recordings (EMGICs). ICA was also used to calculate the coupling between the simultaneously recorded EEG and the EMG from a single muscle (Subject 1) or the EMGICs (Subject 2). The EMGICs were either tonic or phasic. The significant couplings between the EEG and the EMGICs were different for each EMGIC. The distribution on the scalp of the coupling between the EEG and tonic EMGICs and those of the single-muscle EMG were similar and followed topographic patterns in sensorimotor regions. Couplings between the EEG and phasic EMGICs were bifrontal, lateral, and bioccipital and were significantly stronger than the coupling between a single muscle's EMG and the EEG (p < 2 x 10(-5)) or another EMG combination derived from principal component analysis. These preliminary results support the notion that electrophysiological cortical activations are more significantly related to the ICs of muscle activations than to the activations of individual muscles alone.

Identification of motor pathways during tumor surgery facilitated by multichannel electromyographic recording

The goal of this study was to determine the usefulness of electromyographic (EMG) recording in locating motor pathways near the central sulcus or internal capsule during surgery. Multichannel EMG recordings were compared with visual observation of contralateral body movement that was elicited by direct cortical or subcortical stimulation used to identify motor pathways before and during tumor resection. The EMG recordings were more sensitive than visual observation alone in identifying motor responses: in 30% of cases, responses were identified by EMG recording alone at some point during the operation and, in 9% of cases, EMG responses were the only responses observed. Additionally, EMG recordings often detected seizure activity resulting from electrical stimulation of the cortex that could not be appreciated on visual inspection. No new motor deficits were seen postoperatively in 88% of the patients in this series. Using EMG recording in addition to motor pathway mapping results in greater sensitivity, allowing the use of lower stimulation levels and facilitating detection of stimulation-induced seizure activity.

Spatio-temporal representation of multichannel EMG firing patterns and its clinical applications

Analyzing motor unit (MU) activity is essential for studying the neurological dysfunction of upper motor neuron disorders (UMND). This study employs multichannel surface electromyographic (EMG) signals, as recorded from the upper arm during elbow flexion and extension, to analyze the temporal changes and spatial distribution of the dominant firing rate. To estimate the dominant firing rate, the autoregressive (AR) spectrum analysis method is utilized to detect the peaks and poles of the AR model, of the surface EMG spectrum below 40 Hz. The temporal changes in firing rates are also observed by using the spectrogram representation of low-frequency EMG spectra. The EMG spectrogram facilitates examination of the time-varying characteristics of firing rates and recruitment of MUs from surface EMG signal. The low-frequency spectra of multichannel EMG are then represented in a polar form to visualize the spatial distribution of firing patterns across muscles. Via spatio-temporal representation techniques, this study provides a viable approach of observing both the spatial and temporal patterns of MU activities in normal subjects and patients with UMND, including cerebrovascular disease and Parkinson's disease.

Physiological cost of horizontal materials handling while seated

Experiments were carried out in the course of which during seated work a load of 2 kg had to be lifted repeatedly 24 times per minute from 3 different beginning points within the outward reach over a distance of 38 cm to a fixed point near the body. In order to measure the physiological cost strictly due to unweighted movements, identical tasks had been performed by handling an almost weightless article (i.e. 0 kg). Besides oxygen consumption and heart rate as integral measures for stress and strain, electromyographic activity (EA) of 7 muscle groups was registered continuously from each of 11 subjects participating in the test sessions. EA was standardized with the help of EA-values obtained from preceding maximum voluntary contractions (MVC). The results show extensive and consistent reactions of the global and local indicators of strain. Dependent on direction, even manual movements without external load induced strain, elucidated in significant minimum values of all parameters at 30° (measured from the frontal plane of the subjects). The local strain of the 7 monitored muscles shows a more or less distinct dependence of the direction. Almost only the dynamic component is influenced, yet to a degree which is much higher than the reaction of the integral physiological parameters. Correlations between EA-values and those of the oxygen consumption as well as the work pulses indicate that electromyography is an efficient method for determining local muscular strain, which can be assessed very precisely. Furthermore, multi-channel electromyography proved to enable detection of bottle-necks in muscular strain.

Multichannel Electromyographic Observations in Spasmodic Dysphonia Patients and Normal Control Subjects

Spasmodic dysphonia is primarily a disorder of vocalization. Increasing evidence, however, suggests that individuals with this disorder comprise a heterogeneous population characterized by abnormal motor control throughout the vocal tract. Multichannel simultaneous electromyography was performed on 11 spasmodic dysphonia patients and 10 normal awake subjects to investigate both the distribution of neuromotor abnormality within the vocal tract (eg, intrinsic and extrinsic laryngeal muscles, tongue, and palate) and the contribution of activation of higher central nervous system centers to observed abnormality. Experimental tasks ranged from vegetative (quiet breathing) to simple linguistic (short sentences). Digitized electromyographic signals were analyzed to compute the amplitude envelope and extract a set of parameters that represent amplitude characteristics. Electrode insertions were cross-validated by quantitative analysis of patterns of activation across selected reference tasks and by traditional qualitative methods. Between-group differences were found for measures of normalized median and peak token amplitudes. These differences are both task- and measure-dependent. Results highlight the complex and interactive effects of muscle, task, and quantitative measures on between-group differences.

Objektivierung der Muskelaktivität bei krankengymnastischen Bewegungsabläufen mit Mehrkanalelektromyographie

Several exercises to strengthen trunk muscles were studied using multichannel electromyography. The single exercises resulted in different degrees of activation, not only of single muscles, but of whole muscle chains. Within these chains, special attention was given to weakened muscles. By training kinesthesia, clear commands and facilitation, their activation could be increased. This resulted in practical consequences for aimful medical gymnastics for diseases of the spine.

Local muscular strain dependent on the direction of horizontal arm movements.

Manual material handling still plays an important role in assembly work as well as in the service industry. By means of an ergonomic layout of working places, the effects of disadvantageous working conditions, especially static load resulting from unfavourable postures of the body as well as unnecessary physiological cost arising from body movements may be avoided. In this context knowledge about the optimum directions of horizontal arm movements is fundamental. Therefore by means of advanced methods of multi-channel electromyography (EMG) and applying computer assisted evaluation methods, physiological responses to one-handed horizontal material handling in a sitting position were recorded. In order to obtain myoelectric signals from the most important task-relevant muscles out of more than 40 muscle groups of the hand-arm-shoulder-system, preceding research was done also aiming at standardized lead positions for surface EMG. Groups of five young females each participated in a series of successive experiments, in which the direction of movements of the left arm was varied. The subjects worked without and with an external load imposed by weights of 0, 1, 2 and 4 kg. The movements between 20 degrees and 230 degrees--measured from the frontal plane of the subjects--included working from ahead and from behind. The lifting distance was 38 cm starting from different outward points within the reach to a fixed point near the body. Also in one test series the handling frequency was varied between 12, 24 and 48 lifts per minute. Assessment of the physiological cost by electromyographic activities (EA), especially the determination of the most stressful and least expensive directions of repetitive horizontal movements, was more effective when differentiating static and dynamic portions of muscular strain than common means of EA.

Laryngeal control for voicing distinction in Japanese consonant production.

The aim of the present study was to investigate the laryngeal adjustments for voiced versus voiceless distinction in Japanese consonant production by means of laryngeal electromyography (EMG) and fiberoptic observation. Multichannel EMG recordings were taken of a Japanese subject and the data were computer-processed to obtain the averaged activity patterns of the five intrinsic laryngeal muscles with special reference to the voicing distinction in consonant production in various phonetic environments. It was found that there were apparent reciprocal patterns in the posterior cricoarytenoid (PCA) and the interarytenoid (INT) in terms of significant negative correlation, and active control of PCA for voicelessness was demonstrated. The patterns of the thyroarytenoid and the lateral cricoarytenoid were different from that of INT even though these two muscles are usually classified as the members of the adductor group, and their activity levels were apparently influenced by the phonetic environment. A possible contribution of the cricothyroid (CT) to the voicing distinction was also pointed out but further investigations on acoustic parameters seem to be mandatory in more critical interpretation of CT activity in speech.

Electromyography of the human cheeks and lips.

AbstractTo clear up indecision and disparities in the literature of muscular functions in the cheek and lips, multichannel electromyography with fine‐wire intramuscular electrodes was used in eight subjects. Both facial expressions and musical performance were investigated. Intersubject variations were common in the various muscles and intrasubject variation also appeared. The production of specific notes at specific volume on the trumpet or trombone did not depend on exact patterns of activity in the muscles of the lips and buccinator. Gentle puffing out of the cheek produces little or no activity in any muscle, but when this is done forcefully the orbicularis oris activity is marked. Buccinator can be kept deliberately relaxed or active during puffing. Smiling always produces buccinator activity as does forceful retraction of the corners of the mouth. Levator anguli oris activity always recruits concurrent buccinator activity but the reverse is not true.