Surface EMG Parameters Research Articles

Ictal quantitative surface electromyography correlates with postictal EEG suppression

ObjectiveTo test the hypothesis that neurophysiologic biomarkers of muscle activation during convulsive seizures reveal seizure severity and to determine whether automatically computed surface EMG parameters during seizures can predict postictal generalized EEG suppression (PGES), indicating increased risk for sudden unexpected death in epilepsy. Wearable EMG devices have been clinically validated for automated detection of generalized tonic-clonic seizures. Our goal was to use quantitative EMG measurements for seizure characterization and risk assessment.MethodsQuantitative parameters were computed from surface EMGs recorded during convulsive seizures from deltoid and brachial biceps muscles in patients admitted to long-term video-EEG monitoring. Parameters evaluated were the durations of the seizure phases (tonic, clonic), durations of the clonic bursts and silent periods, and the dynamics of their evolution (slope). We compared them with the duration of the PGES.ResultsWe found significant correlations between quantitative surface EMG parameters and the duration of PGES (p < 0.001). Stepwise multiple regression analysis identified as independent predictors in deltoid muscle the duration of the clonic phase and in biceps muscle the duration of the tonic-clonic phases, the average silent period, and the slopes of the silent period and clonic bursts. The surface EMG-based algorithm identified seizures at increased risk (PGES ≥20 seconds) with an accuracy of 85%.ConclusionsIctal quantitative surface EMG parameters correlate with PGES and may identify seizures at high risk.Classification of evidenceThis study provides Class II evidence that during convulsive seizures, surface EMG parameters are associated with prolonged postictal generalized EEG suppression.

Nonlinear parameters of surface EMG in schizophrenia patients depend on kind of antipsychotic therapy.

We compared a set of surface EMG (sEMG) parameters in several groups of schizophrenia (SZ, n = 74) patients and healthy controls (n = 11) and coupled them with the clinical data. sEMG records were quantified with spectral, mutual information (MI) based and recurrence quantification analysis (RQA) parameters, and with approximate and sample entropies (ApEn and SampEn). Psychotic deterioration was estimated with Positive and Negative Syndrome Scale (PANSS) and with the positive subscale of PANSS. Neuroleptic-induced parkinsonism (NIP) motor symptoms were estimated with Simpson-Angus Scale (SAS). Dyskinesia was measured with Abnormal Involuntary Movement Scale (AIMS). We found that there was no difference in values of sEMG parameters between healthy controls and drug-naïve SZ patients. The most specific group was formed of SZ patients who were administered both typical and atypical antipsychotics (AP). Their sEMG parameters were significantly different from those of SZ patients taking either typical or atypical AP or taking no AP. This may represent a kind of synergistic effect of these two classes of AP. For the clinical data we found that PANSS, SAS, and AIMS were not correlated to any of the sEMG parameters. Conclusion: with nonlinear parameters of sEMG it is possible to reveal NIP in SZ patients, and it may help to discriminate between different clinical groups of SZ patients. Combined typical and atypical AP therapy has stronger effect on sEMG than a therapy with AP of only one class.

Surface EMG parameters in schizophrenia patients.

The aim of the study was to compare a variety of surface EMG (sEMG) parameters in several groups of schizophrenia (SZ, n=69) patients and healthy controls (n=44). We computed spectral, mutual information (MI) based and recurrence quantification analysis (RQA) parameters of sEMG. The major finding is that sEMG of the controls had higher values of the MI-based parameter, mean and median spectrum frequencies, and lower values of most of RQA parameters. It means higher content of recurrent fragments in sEMG of SZ patients. We suggest that the differences might be caused by either denervation/renervation process of single muscle fibers in SZ patients and/or by increased motor unit synchronization induced by antipsychotic therapy.

Therapeutic application of Botulinum Toxin A in patients with local muscle dystonia and oral dyskinesia

Botulinum Toxin Type A has been introduced as new therapeutic regime in neurological, cosmetic, urinary, gastrointestinal and pain-related conditions. The use of Botulinum Toxin A in craniomandibular disorders is discussed controversially. Local muscle dystonia is defined as movement disorder in combination with sustained muscle contractions. Contortion, repetitive movements and atypical posture are frequently seen symptoms in such cases. The movements are involuntary and often painful. A single muscle or a group of muscles, even the whole body may be involved. Oral dyskinesias are involuntary repetitive movements of the mouth and face. Severe bruxism can be included in this form of movement disorder. Within this study, patients diagnosed with severe bruxism or local muscle dystonia including oral dyskinesia were examined with electromyography before and after treatment. Subjects were randomly allocated to either myo-relaxation medication and relaxation splint therapy or to Botulinum Toxin A injection therapy. Surface EMG parameters of chewing and neck muscles were used to judge the treatment effects. A positive impact of BTA on EMG-characteristics, reflecting the functional condition of facial muscles, had been detected. BTA injections seem to have a positive effect in patients with bruxism and local muscle dystonia. An increased quantity of mandibular movements and a better coordination can be observed after BTA injection. In comparison with a standard myo relaxation therapy, the effects of BTA treatment are more distinct and long standing. BTA appears to be a promising therapeutic regime in patients with focal muscle dystonia and oral dyskinesia. A confirmed diagnosis and lege artis application by experienced clinicians constitute as sine qua non. Further studies are required to improve our knowledge in Botulinum Toxin A treatment of muscle dystonia and dyskinesia.

Back muscle activation pattern and spectrum in defined load situations

For the prevention and rehabilitation of low back pain the understanding muscle function in the low back region is essential. Important aspects of function include the muscle activation patterns and muscle fatigue. In the low back region m. erector spinae plays a critical role. The different parts of this muscle complex differ considerably in function. Following the concept of Bergmark [A. Bergmark, Stability of the lumbar spine, Acta Orthop. Scand. 60 (1989) 1–54] trunk muscles can be divided in two subsystems, the global-mobilizing-system and the local-stabilizing-system. At present the multifidus muscles are assigned to the local whereas the longissimus and iliocostalis muscles are assigned to the global system. From results of the four parts of our investigation, it can be shown that essential information about muscle function can be obtained by spectral and intra- as well as inter-muscular surface EMG parameters. Obtained data demonstrated functional transitions between the local and global system of trunk muscles for the multifidus muscle.

Repeatability of surface EMG parameters at various isometric contraction levels and during fatigue using bipolar and Laplacian electrode configurations

The objective of this work was to assess the repeatability of two surface electromyographic (sEMG) recording techniques, the classical bipolar configuration and a Laplacian configuration to document their ability to provide reliable information during follow-up studies. The signals were recorded on 10 healthy subjects during voluntary isometric contractions of the biceps brachii muscle at different constant contraction levels. Slopes, area ratios (at 60% of the maximal voluntary contraction (MVC)) and initial values (at 20%, 40%, 60%, 80% and 100% MVC) of the root mean square (RMS), the mean power frequency (MPF) and the muscle fibre conduction velocity (CV) were estimated. Experimental sessions were repeated on three different days with both electrode sets to evaluate the repeatability of sEMG parameter estimates. Classical results were observed, such as an increase in the RMS and the CV with the contraction level. Only initial values of RMS and MPF were shown to be dependent on electrode type. These two parameters presented intra-class correlation coefficient values higher than .80 for high contraction levels. On the whole, the repeatability of the measures was good; however it was better for all sEMG parameter estimates with bipolar electrodes than Laplacian electrodes. Because a bipolar configuration is less selective than a Laplacian one, it provides a global view of muscular activity, which is more repeatable, hence more suitable for follow-up studies.

139 Changes in surface EMG parameters during an isometric endurance task

139 Changes in surface EMG parameters during an isometric endurance task

Chronic hypobaric hypoxia does not affect electro-mechanical muscle activities during sustained maximal isometric contractions.

The aim of the study was to evaluate the influence of chronic hypobaric hypoxia [43 days at 5050 m above sea level, a.s.l.] on the electrical and mechanical activities of the elbow flexor and knee extensor muscles during sustained maximal isometric contractions. Seven subjects participated in this study. The maximal voluntary contraction (MVC) of the two muscle groups was assessed. The subjects were then asked to perform a sustained MVC for 1 min, during which surface EMG and MMG signals were recorded before (SL) and after 43 days at high altitude (HA). From the time and frequency domain analysis of the surface EMG and MMG, the root mean square (RMS) and the mean frequency (MF) were then calculated. After HA exposure, in both the investigated muscle groups the results showed that: (1) the MVC did not change; (2) the maximum force decay during the sustained MVC was similar; (3) surface EMG and MMG parameters did not show any statistical difference. These data suggest that exposure to HA did not affect the electrical and mechanical properties of the two investigated muscle groups. We conclude that exposure to chronic hypobaric hypoxia seems to have no effect on the central motor drive or on muscle performance during sustained maximal isometric contractions of the active muscles.

The effect of an active warm-up on surface EMG and muscle performance in healthy humans.

The effect of an active warm-up on maximal voluntary contraction (MVC), maximal instantaneous power output and surface EMG (sEMG) parameters was studied. Eight volunteers [mean (SD) 22 (4) years] completed two trials on the same day, one control (CO), and the other preceded by an active cycling warm-up (WU) at 70% ventilatory threshold determined by the ventilatory equivalent method. Quadriceps muscle temperature, measured from vastus lateralis with a flexible thermistor, was 33.8 (0.4) degrees C in CO compared to 36.8 (0.5) degrees C in WU ( P<0.05). Aural temperature, measured by an infrared tympanic thermistor, was not different between conditions. Experimental trials consisted of three knee-extension maximum voluntary contractions at a 90 degree angle with simultaneous recording of sEMG from the vastus lateralis, followed by three squat jumps performed on a force platform. SEMGs were analysed in the frequency domain as median frequency (MDF) and in the time domain as root mean square (RMS). MDF was 59.2 (14.1) Hz in CO compared to 67.2 (11.8) Hz in WU ( P<0.05), while RMS was higher in CO compared to WU [0.65 (0.28) mV vs. 0.56 (0.19) mV; P<0.05]. MVC was not different [465.7 (107.6) N vs. 490.1 (117.2) N], whilst instantaneous power output during the squat jump was significantly higher in the WU trial [3324 (866) W vs. 3569 (919) W; P<0.05]. These data show MDF to be altered with an active warm-up, which would relate to a greater conduction velocity. This may translate into faster activation of the muscle fibres, thus partly explaining the increase in power output.

Changes in surface EMG parameters during static and dynamic fatiguing contractions

The effect of contraction types on muscle fiber conduction velocity (MFCV), median frequency (MDF) and mean amplitude (AMP) of surface electromyography was examined in the vastus lateralis of 19 healthy male adults. The subjects performed knee extension both statically and dynamically until they were exhausted. The static contraction was a sustained isometric extension of the knee at a joint angle of 90° with 50% of the maximum voluntary contraction (MVC) load. The dynamic contraction was a repetitive isotonic extension of the knee between the angles of 90° and 180° with the same 50% MVC load at a frequency of 10 times per minute. MFVC during the static contraction significantly decreased during the exercise ( p<0.01). On the other hand, MFVC during the dynamic contraction did not significantly change throughout the exercise. MDF decreased and AMP increased during both types of contractions ( p<0.01). Because the blood flow within the muscle is maintained during the dynamic contraction by enhanced venous return from the contracting muscle, these results suggested that MFVC is affected by the metabolic state in the muscle and the changes in MDF cannot be explained only by that of MFVC.

Motor unit size estimation: confrontation of surface EMG with macro EMG

Surface EMG (SEMG) is little used for diagnostic purposes in clinical neurophysiology, mainly because it provides little direct information on individual motor units (MUs). One of the techniques to estimate the MU size is intra-muscular Macro EMG. The present study compares SEMG with Macro EMG. Fifty-eight channel SEMG was recorded simultaneously with Macro EMG. Individual MUPs were obtained by single fiber triggered averaging. All recordings were made from the biceps brachii of healthy subjects during voluntary contraction at low force. High positive correlations were found between all Macro and Surface motor unit potential (MUP) parameters: area, peak-to-peak amplitude, negative peak amplitude and positive peak amplitude. The MUPs recorded with SEMG were dependent on the distance between the MU and the skin surface. Normalizing the SEMG parameters for MU location did not improve the correlation coefficient between the parameters of both techniques. The two measurement techniques had almost the same relative range in MUP parameters in any individual subject compared to the others, especially after normalizing the surface MUP parameters for MU location. MUPs recorded with this type of SEMG provide useful information about the MU size.

Muscle fiber conduction velocity in the diagnosis of familial hypokalemic periodic paralysis--invasive versus surface determination.

Muscle fiber conduction velocity (MFCV) in the brachial biceps muscle was determined in a large family of patients with hypokalemic periodic paralysis (HOPP) by both a surface and an invasive method. Other surface EMG parameters and the muscle force were also determined. Both the surface and the invasive method showed a significantly lower mean MFCV in the proven gene carriers but only the invasive method showed a lower MFCV in all proven carriers. It can be concluded that MFCV determination is a reliable method to detect the membrane defect in HOPP carriers and that the invasive method is not only easy to perform, but also more sensitive. The muscle force and the integrated EMG at maximal voluntary contraction were lower in the carrier group. A positive correlation between the surface MFCV and the neuromuscular efficiency (the quotient of force and integrated EMG) was found in the controls but not in the HOPP carriers. Since type II fibers have a higher neuromuscular efficiency, this suggests a preferential involvement of type II fibers in HOPP.

Variability and interrelationships of surface EMG parameters during local muscle fatigue

The inter- and intraindividual variability of the frequency power density spectral and surface EMG amplitude parameters and of the muscle fiber conduction velocity (MFCV) is studied in 26 healthy volunteers during fatiguing isometric ischemic intermittent exercise of the m. biceps brachii at 80% of the maximal voluntary contraction level, with a contraction rate of 30/min. No significant age effects were found. Males were significantly stronger compared with females. The higher initial SEMG amplitude and the stronger shift of the frequency power density spectrum (PDS) to lower frequencies appear to be significantly correlated with males. Fatigue induces an almost proportional compression of the SEMG frequency content. The muscle fiber conduction velocity has the highest intraindividual reproducibility (r = 0.81). Despite the definite and strong influence of the MFCV on the PDS, the shift of the PDS can not be explained by a change of MFCV alone.

Simultaneous measurement of surface EMG and movements for clinical use.

A system for simultaneous measurement of surface EMG, joint movement and temporal parameters of gait has been developed for clinical use. Some design constraints, imposed by the clinical situation, are indicated. Multiple cycles of movement are recorded and averaged patterns of muscle activation and joint movements are determined. Data processing runs concurrently with data acquisition, so that the results are available for clinical interpretation immediately after the measurement. Instrumentation, signal processing and software are described and some examples of application of the system for evaluation of therapies and functional aids are presented. It is proposed that clinically relevant quantitative information can be obtained by comparison of different recordings of the individual patient rather than comparison with patterns found with normal subjects.

Conduction velocity in ischemic muscle: effect on EMG frequency spectrum.

Conduction velocity in ischemic muscle: effect on EMG frequency spectrum.