Surface Electromyography Measurements Research Articles

A new table for work with a microscope, a solution to ergonomic problems

Microscope workers are exposed to continuous static muscular work and an increased risk of musculoskeletal disorders in the neck, shoulder and upper extremities. In a Finnish research centre, microscope workers reported pain in the shoulder, neck, lower back and upper back. As a consequence, a programme to solve the ergonomic problems of microscope work was initiated and led to the construction of a new table for microscopes. Ten experienced male microscope workers were chosen as subjects to carry out an experimental study in which the new table and an old one, an ordinary non-adjustable laboratory table, were compared in a standardized microscope task. The dependent variable was the electromyographic activity measured from muscles in the neck–shoulder region. The new table allowed the microscope to be used with the head in an upright position, the forearms supported and with less flexion of the upper arm. Surface electromyographic measurements also confirmed that the changes were ergonomic improvements.

Evaluation of driver discomfort during long-duration car driving

The evolution of indices of fatigue, discomfort, and performance of subjects seated for long duration (150 min) in car seats were studied ( n=11). Four experimental configurations were used: with and without vibration for two seats (U, uncomfortable; C, comfortable). Surface electromyography (SEMG) data were recorded bilaterally from cervical erector spinae and external oblique muscles. Discomfort increased significantly during the trial, regardless of the experimental condition ( p<0.05). Performance was significantly worse for seat U with vibration ( p<0.05). The median frequency of SEMG signals did not change between experimental conditions or across time. It would appear that, either the level of discomfort experienced was insufficient to change either performance or SEMG measures, or that the large parameter estimation variance of the SEMG signals might have masked any underlying spectral change. Further refinement of the SEMG signal processing methodology may be necessary to be able to detect fatigue of postural muscles.

Cervical muscle dysfunction in chronic whiplash-associated disorder grade 2: the relevance of the trauma.

Surface electromyography measurements of the upper trapezius muscles were performed in patients with a chronic whiplash-associated disorder Grade 2 and those with nonspecific neck pain. To determine the etiologic relation between acceleration-deceleration trauma and the presence of cervical muscle dysfunction in the chronic stage of whiplash-associated disorder. From a biopsychosocial perspective, the acceleration-deceleration trauma in patients with whiplash-associated disorder is not regarded as a cause of chronicity of neck pain, but rather as a risk factor triggering response systems that contribute to the maintenance of neck pain. One of the contributing factors is dysfunction of the cervical muscles. Considering the limited etiologic significance of the trauma, it is hypothesized that in patients with neck pain, there are no differences in muscle activation patterns between those with and those without a history of an acceleration-deceleration trauma. Muscle activation patterns, expressed in normalized smooth rectified electromyography levels of the upper trapezius muscles, in patients with whiplash-associated disorder Grade 2 were compared with those of patients with nonspecific neck pain. The outcome parameters were the mean level of muscle activity before and after a physical exercise, the muscle reactivity in response to the exercise, and the time-dependent behavior of muscle activity after the exercise. There were no statistical significant differences in any of the outcome parameters between patients with whiplash-associated disorder Grade 2 and those with nonspecific neck pain. There was only a tendency of higher muscle reactivity in patients with whiplash-associated disorder Grade 2. It appears that the cervical muscle dysfunction in patients with chronic whiplash-associated disorder Grade 2 is not related to the specific trauma mechanism. Rather, cervical muscle dysfunction appears to be a general sign in diverse chronic neck pain syndromes.

Three-Layer Volume Conductor Model and Software Package for Applications in Surface Electromyography

On comparing multichannel surface electromyographic measurements of the m. biceps brachii with simulations performed with a previously developed two-layer volume conduction model, we found substantial discrepancies. To incorporate an apparent distorting effect of the skin tissue, the model was extended to three layers. This new model describes the potential resulting from an eccentric bioelectric source in a finite, cylindrical, and anisotropic volume conductor consisting of three layers, representing muscle, subcutaneous fat, and skin tissue. This contribution presents the governing mathematical equations of the three-layer volume conductor model as well as our approach to their solution. A comparison of various models shows that the three-layer model best describes measured potential distributions. Furthermore, we present the "ANVOLCON" (analytical volume conductor) software package. This package has been developed to facilitate the use of the model for scientific and educational purposes and is freely available from http://www.mbfys.kun.nl/knf

Influence of interelectrode distance and force level on the spectral parameters of surface electromyographic recordings from the lumbar muscles

In order to study the influence of interelectrode distance and force level on the electromyographic (EMG) spectral parameters and on their reliability, bipolar surface EMG measurements were performed on the lumbar muscles of 15 subjects. Two test contractions (45 s) at 40% of maximal voluntary contraction (MVC) were performed, one with 2 cm interelectrode distance and the other with 4 cm, followed by two contractions at 80% MVC with the same change in interelectrode distance. Increasing the interelectrode distance from 2 to 4 cm caused a significant mean decrease (about 8%) in the initial median frequency. It is shown that this shift is of an order of magnitude that may be expected from the bipolar electrode filter factor, and we further conclude that the observed individual variations in the shift are likely to be connected to fluctuations in the shape of the power spectrum and to variations in conduction velocity. No significant change was found for the median frequency slope when changing the interelectrode distance. Increasing the force (from 40 to 80% MVC) also caused a significant mean decrease (about 10%) in the initial median frequency. The median frequency slope became significantly more negative by more than 200%. We conclude, however, that torque fluctuations during the fatigue contractions should have had only minor influence on the standard error of measurement of the initial median frequency and of the median frequency slope.

Electromyographic Power Spectral Analysis of the Paraspinal Muscles: Reliability study

Summary Background and Purpose Despite previous studies on the reliability of median frequency (MF) and median frequency slope (MFS) as specific surface electromyography (SEMG) measures of back muscle function, there is still no general consensus regarding the results. A reliability study was carried out to determine the test-retest reliability (within and between-days) of SEMG power spectral analysis of paraspinal muscle activity in healthy subjects. Methods Fifteen volunteer subjects with no history of low back pain were tested. The unsupported trunk holding position was used to measure initial MF and MFS three times. Two measurements were taken on the same day with five minutes interval and the third was taken one week later. Results For initial MF, the high ICC values (0.82-0.92) and high level of agreement between measurements for multifidus and iliocostalis indicated high within and between-days reliability. For MFS, the ICC values (0.65-0.82) and high (for multifidus) to moderate (for iliocostalis) level of agreement between measurements demonstrated high within-day reliability for multifidus and moderate for iliocostalis. Between-days reliability of MFS was found to be good for multifidus and moderately good for iliocostalis with ICC values of 0.60-0.85 and high to moderate level of agreement. Conclusion In this study the SEMG power spectral analysis was shown to be a reliable method of measuring back muscle activity in an unsupported trunk holding test, when measurements are taken in healthy subjects by the same investigator.

Cervical muscle dysfunction in the chronic whiplash associated disorder grade II (WAD-II).

In a cross-sectional study, surface electromyography measurements of the upper trapezius muscles were obtained during different functional tasks in patients with a chronic whiplash associated disorder Grade II and healthy control subjects. To investigate whether muscle dysfunction of the upper trapezius muscles, as assessed by surface electromyography, can be used to distinguish patients with whiplash associated disorder Grade II from healthy control subjects. In the whiplash associated disorder, there is need to improve the diagnostic tools. Whiplash associated disorder Grade II is characterized by the presence of "musculoskeletal signs." Surface electromyography to assess these musculoskeletal signs objectively may be a useful tool. Normalized smoothed rectified electromyography levels of the upper trapezius muscles of patients with whiplash associated disorder Grade II (n = 18) and healthy control subjects (n = 19) were compared during three static postures, during a unilateral dynamic manual exercise, and during relaxation after the manual exercise. Coefficients of variation were computed to identify the measurement condition that discriminated best between the two groups. The most pronounced differences between patients with whiplash associated disorder Grade II and healthy control subjects were found particularly in situations in which the biomechanical load was low. Patients showed higher coactivation levels during physical exercise and a decreased ability to relax muscles after physical exercise. Patients with whiplash associated disorder Grade II can be distinguished from healthy control subjects according to the presence of cervical muscle dysfunction, as assessed by surface electromyography of the upper trapezius muscles. Particularly the decreased ability to relax the trapezius muscles seems to be a promising feature to identify patients with whiplash associated disorder Grade II. Assessment of the muscle (dys)function by surface electromyography offers a refinement of the whiplash associated disorder classification and provides an indication to a suitable therapeutic approach.

Upper Extremity Exposure among Wood Processing Operators

The main goal of this study was to quantify risk factors, that may contribute to the development of musculoskeletal injuries, in a trimmer's job of a large sawmill. Two operators participated in this study and each was measured for two days when two different products were processed. Detailed observational methods were used to quantify task distribution, repetitiveness of hand exertion and work postures. Surface electromyographic (EMG) and electrogoniometric measurements were employed to quantify muscle loads on four muscles in the neck/shoulder and forearm regions, and postural loads of the right wrist and forearm. Results of task distribution showed that the operators spent about 76% of the time monitoring and positioning boards. Thus, ergonomic intervention measures may need to be focused on improvements on this task. Major risk factors found at this job were high repetitive hand exertion, awkward wrist postures, high hand force exertion and static shoulder muscle load.

Multielectrode surface EMG for noninvasive estimation of motor unit size.

To noninvasively estimate the motor unit size, we present a novel surface electromyographic (EMG) measurement system consisting of a surface multielectrode with four-pin electrodes and a pair of surface-disk electrodes. Surface motor unit action potentials (MUAPs) were recorded with the multielectrode, in the so-called multielectrode surface EMG (MSEMG), which was spatially filtered to localize the sensing area and reduce the noise. In addition, a modified decomposition algorithm, considering the geometrical configuration of the multielectrode, was designed to identify the individual MUAPs in the measured MSEMG. The identified MUAP was subsequently used as the triggering source for the EMG signals recorded by the surface-disk electrodes. From a pool of 34 subjects with neuromuscular diseases and 14 normal subjects, the median amplitudes of surface-disk EMG after spike-triggered averaging, called MSEMG-MUAP, correlated well (r = 0.82, P < 0.0001) with those of macro EMG. Moreover, the MSEMG-MUAP recording during a ramp force contraction exhibited the common size principle phenomenon during motor unit recruitment. The results of this study demonstrate that the MSEMG-MUAP measurement is a feasible approach for estimating the motor unit size from the skin surface.

Back and hip extensor muscle function during therapeutic exercises

Background: Therapeutic exercises are widely used in the treatment of low back problems. Clinical knowledge about targeting the load in these exercises, however, is insufficient. This study assessed the L2 and L5 level paraspinal and gluteus maximus muscle activities in different therapeutic exercises. Intramuscular and surface electromyography (EMG) measurements were obtained to study whether surface EMG measurements can be used in the assessment of multifidus muscle function. Methods: Eleven healthy subjects (5 men, 6 women) 21 to 38 years of age volunteered for the study. The subjects performed 18 different therapeutic exercises. During the exercises paraspinal EMG was recorded using fine wire and surface electrodes. The normalized peak and average muscle EMG activities (percentage of amplitude in maximal voluntary contraction [MVC]) during each task were determined. Results: The correlations between the average intramuscular and surface activities of the normalized EMG (% of MVC) at the L2 and L5 levels were .928 and .950, respectively. The peak and average EMG amplitudes of the exercises were below 50% and 25% of MVC, respectively. At the L5 level, the multifidus peak and average EMG amplitudes (% MVC) were higher in women than in men, whereas no significant difference was found at the L2 level. In women, the normalized multifidus EMG amplitude was higher at the L5 level than at the L2 level, whereas no significant difference was found in men. In both sexes, the normalized EMG amplitude was higher in the multifidus than in the longissimus muscle. Conclusion: Surface EMG measurements may be used in the assessment of multifidus muscle function. Simple therapeutic exercises are effective in activating the lumbar paraspinal muscles.

Reliability of surface electromyographic measurements

Objectives: The aim of the study was to investigate short-term, intermediate-term and long-term reliability of surface electromyographic (EMG) measurements.Methods: Eighteen healthy subjects performed 810 isometric knee extension tests. Reliability for maximum voluntary contraction (MVC) and 50% MVC was assessed with retest intervals of 3 min, 90 min and 6 weeks. Reliability for sustained contractions was assessed with retest intervals of 90 min and 6 weeks. EMG was recorded from the rectus femoris, vastus lateralis and vastus medialis muscles. The root mean square (RMS) and the median frequency (MF) parameters were extracted. At sustained contraction tasks, estimated linear regression values of both parameters were analyzed. Bland-Altman-plots, coefficient of repeatability, Pearson's coefficient of correlation and intra class correlation (ICC) procedures were applied to assess test-retest reliability.Results: EMG recordings taken at short-term intervals were generally better reproducible than those of the longer-term intervals. Moreover, 50% MVC EMG recordings demonstrated better reproducibility than 100% MVC measurements, and EMG recorded from the rectus femoris were more constant than that from the vastus lateralis or vastus medialis. The MF parameter recorded from the rectus femoris was the only reliable parameter of EMG fatigue change.Conclusion: In our set up, EMG measurement is best suited for clinical applications if submaximal MVC measurements are performed and signal is taken from rectus femoris muscle.

Classification of paraspinal muscle impairments by surface electromyography.

The purpose of this article is to provide an overview of research to develop surface electromyographic (EMG) measurements for classification of paraspinal muscle impairments in persons with low back pain (LBP). The process of developing laboratory and clinically based protocols is described. Results of studies to evaluate the reliability of these measurements and their relationships with impairments and function are discussed. Research efforts to incorporate EMG spectral measurements, such as the median frequency, into a classification system to identify different types of muscle impairments are documented. Discriminant functions have been calculated based on case-control studies to identify 2 kinds of LBP impairments from constant-force isometric tasks: (1) excessive fatigue due to muscle deconditioning and (2) inhibition of muscle activation secondary to pain or pain-related behaviors. New areas of investigation designed to improve the classification accuracy of such functions using procedures other than discriminant analysis are described. Work in progress to extend the application of the technique to tasks other than those involving just isometric contraction, including those involving repetitive trunk movement, is also described.

Electromyographic activity of the long digital extensor muscle in the exercising Thoroughbred horse.

Surface electrodes were used to record electromyographic (EMG) activity of the long digital extensor muscle on the right hindlimb of 8 Thoroughbred horses for 8 s at the walk and 8 s at the trot before (unfatigued) and after (fatigued) an exercise test. The exercise test was performed on a motorised treadmill set on a 10% grade. Each test started at a speed of 6 m/s which was increased by 1 m/s each minute until the horse fatigued as indicated by its inability to keep pace with the treadmill with minimal encouragement. Observations were made on the horses prior to conditioning (untrained state) and after 8 weeks of regular exercise (trained state). The mean root-mean-square (rms) values of EMG bursts collected in each experimental trial were determined for each horse and group means were derived from the mean of independent subjects. Statistical comparisons for differences in rmsEMG were related to gait, fatigue and training. Mean rmsEMG at the trot was consistently higher than at the walk (P<0.05). At the walk, mean fatigued rmsEMG tended to be higher than the mean unfatigued rmsEMG in the untrained state and was significantly higher in the trained state (P<0.05). At the trot, mean fatigued rmsEMG was higher (P<0.05) than mean unfatigued rmsEMG in both the untrained and trained states. Training did not have an effect on mean rmsEMG of unfatigued muscles at the walk or the trot (P>0.05). However, fatigued muscles experienced higher EMG activity in the trained state at the walk (P<0.05). A similar tendency was observed at the trot. Results of this study suggest that surface EMG measurement may be useful for evaluating fatigue in exercising horses.

Multisite Surface Electromyography and Complementary Healing Intervention: A Comparative Analysis

A comparative analysis was conducted on a series of three experimental studies that examined the effect of various local and nonlocal (distant) complementary healing methods on multisite surface electromyographic (sEMG) and autonomic measures. The series concentrated sEMG electrode placement on specific neuromuscular paraspinal centers (cervical [C4], thoracic [T6], and lumbar [L3]), along with the frontalis region, due to the fact that these sites corresponded to the location of individual chakra centers as delineated in ancient Eastern medical and philosophical texts. It was hypothesized that the sEMG assessment procedure had the potential to provide objective, quantifiable correlates for complementary healing treatment effects, as well as assess the energy flow through the chakras during a healing treatment. The studies were the first of their kind to incorporate randomized, double-blind, placebo-controlled protocols in order to evaluate correlative neuromuscular multisite sEMG paraspinal measures with different complementary healing treatment interventions. Although the measurement protocols were similar between experiments, the results, demonstrated by the individual studies, varied. Whereas the overall findings of the series are encouraging because they indicate a potential objective scientific correlate to complementary healing treatment intervention, the results are considered preliminary in nature and appear to be linked to either the meditational experience of the subjects or dependent on the particular healer(s) used. Additional research is needed in order to establish the multisite sEMG assessment procedure as a reliable correlative measure for complementary healing treatment effects and to determine whether a consistent replicative treatment effect can be demonstrated independent of the specific subject population or practitioner(s) used.

Changes in paravertebral EMG spectrum parallel to strength increases after rehabilitation in chronic low back pain patients

The aim of this preliminary report was to identify parameters related to functional improvement in healthy subjects and in patients with chronic low back pain (LBP) undergoing an intensive rehabilitation programme. Four healthy controls and four chronic LBP patients were evaluated before and after a four-week rehabilitation programme. Dynamic and static strength tests, namely sustained isometric contractions, and trunk flexion-extension movements were performed in conjunction with surface electromyographic (EMG) measurements. Significant pre-rehabilitation differences were found between the two groups. Measured forces and the ratio between EMG amplitude values during extension and during flexion changed significantly in LBP patients immediately after rehabilitation. No significant changes were found in the control subjects after the rehabilitation programme. After rehabilitation, the slope of decay of the median frequency of the EMG power spectrum at L4 level, during a 60-second isometric submaximal (60% MVC) contraction, decreased significantly ( p &lt; 0.02), indicating a lower fatigue level.

The application of generalizability theory to surface electromyographic measurements during psychophysiological stress testing: how many measurements are needed?

Generalizability theory is an extension of classical reliability theory that allows multiple sources of measurement error in an experimental design to be investigated simultaneously. In the present study, generalizability theory was used to evaluate measurement error in psychophysiological test procedures used to differentiate tension headache patients from normal controls based upon measures of electromyographic (EMG) responding. Thirty-three subjects who met diagnostic criteria for tension-type headache and 40 normal control subjects who rarely or never experienced headache participated in two laboratory sessions. EMG activity of head and neck muscles was recorded while subjects performed baseline, relaxation, choice reaction time, psychomotor tracking, and cold pressor tasks. Variance components were computed for an experimental design having subjects nested within experimenters and crossed with sessions and replications. Generalizability coefficients were computed for combinations of various numbers of sessions and replications. The generalizability of EMG measures was highly variable, depending on the experimental conditions in force. The largest sources of measurement error were attributed to the unique responsiveness of individual subjects under a particular set of treatment conditions. For some stress tests currently in use, data from several testing sessions may need to be averaged in order to achieve acceptable levels of generalizability. Generalizability greater than 0.80 can be expected only rarely when data are collected during a single session. In the research setting, low generalizability may account for the failure of EMG-based stress tests to differentiate tension headache patients from controls during stressful task performance. In the clinical setting, the generalizability of information derived from "stress profiling" or muscle "scanning" techniques, which depend on results obtained during a single testing session, is doubtful.

Control of stiffness by the medium latency electromyographic response to limb perturbation

It is hypothesized that the medium latency electromyographic (EMG) response (ML) to limb perturbation functions to preset limb stiffness to a constant initial level. Three predictions are derived from this hypothesis: Firstly, in the presence of an instruction calling for opposition to limb perturbation, a control signal, ML, will be observed and will lead to the establishment of a constant level of limb stiffness. Secondly, in the absence of an instruction to oppose, no control signal will be observed and correspondingly a constant stiffness will not be generated. Thirdly, the latency of onset of stiffness control will covary with the latency of onset of ML. These predictions were tested in experiments involving perturbation of the human forearm about the elbow joint, with surface EMG measurements and computation of the limb stiffness function. The results are in accord with these predictions, and support the hypothesis that ML functions in the feedforward control of limb stiffness.