EMG Spectra Research Articles

Analysis of surface myoelectric signals by linear prediction method

The article presents a proposal to use linear prediction method for a quick analysis of surface myoelectric (EMG) signals. The spectra obtained with the linear prediction (LP) and Fourier methods were compared. The LP method allows for a precise determination of the location and amplitude of the spectrum maximum and observation of changes in muscle tension and contraction phases. EMG spectra of brachial biceps during flexion and extension of the forearm by four adults were analyzed. The optimal width of the time window for the averaging of motor unit action potentials that allows for the observation of changes during contraction was established. It has been found that maximum spectrum during flexion has a significantly higher frequency and amplitude than during the extension of the forearm.

Time–frequency Analysis of the EMG Digital Signals

In the article comparison of time-frequency spectra of EMG signals obtained by the following methods: Fast Fourier Transform, predictive analysis and wavelet analysis is presented. The EMG spectra of biceps and triceps while an adult man was flexing his arm were analysed. The advantages of the predictive analysis were shown as far as averaging of the spectra and determining the main maxima are concerned. The Continuous Wavelet Transform method was applied, which allows for the proper distribution of the scales, aiming at an accurate analysis and localisation of frequency maxima as well as the identification of impulses which are characteristic of such signals (bursts) in the scale of time. The modified Morlet wavelet was suggested as the mother wavelet. The wavelet analysis allows for the examination of the changes in the frequency spectrum in particular stages of the muscle contraction. Predictive analysis may also be very useful while smoothing and averaging the EMG signal spectrum in time.

Spectral properties of electromyographic and mechanomyographic signals during isometric ramp and step contractions in biceps brachii

The purposes of this study were: (1) to apply wavelet and principal component analysis to quantify the spectral properties of the surface EMG and MMG signals from biceps brachii during isometric ramp and step muscle contractions when the motor units are recruited in an orderly manner, and (2) to compare the recruitment patterns of motor unit during isometric ramp and step muscle contractions. Twenty healthy participants (age = 34 ± 10.7 years) performed step and ramped isometric contractions. Surface EMG and MMG were recorded from biceps brachii. The EMGs and MMGs were decomposed into their intensities in time–frequency space using a wavelet technique. The EMG and MMG spectra were then compared using principal component analysis (PCA) and ANCOVA. Wavelet combined PCA offers a quantitative measure of the contribution of high and low frequency content within the EMG and MMG. The ANCOVA indicated that there was no significant difference in EMG total intensity, EMG MPF, first and second principal component loading scores (PCI and PCII) between ramp and step contractions, whereas the MMG MPF and MMG PCI loading scores were significantly higher during ramp contractions than during step contractions. These findings suggested that EMG and MMG may offer complimentary information regarding the interactions between motor unit recruitment and firing rate that control muscle force production. In addition, our results support the hypothesis that different motor unit recruitment strategy was used by the muscle when contracting under different conditions.

Effects of postural muscle fatigue on the relation between segmental posture and movement

The purpose of this study was to examine whether fatigue of postural muscles might influence the coordination between segmental posture and movement. Seven healthy adults performed series of fifteen fast wrist flexions and extensions while being instructed to keep a dominant upper limb posture as constant as possible. These series of voluntary movements were performed before and after a fatiguing submaximal isometric elbow flexion, and also with or without the help of an elbow support. Surface EMG from muscles Deltoı̈deus anterior, Biceps brachii, Triceps brachii, Flexor carpi ulnaris, Extensor carpi radialis were recorded simultaneously with wrist, elbow and shoulder accelerations and wrist and elbow displacements. Fatigue was evidenced by a shift of the elbow and shoulder muscles EMG spectra towards low frequencies. Kinematics of wrist movements and corresponding activations of wrist prime-movers, as well as the background of postural muscle activation before wrist movement were not modified. There were only slight changes in timing of postural muscle activations. These data indicate that postural fatigue induced by a low-level isometric contraction has no effect on voluntary movement and requires no dramatic adaptation in postural control.

Analysis of surface EMG of human soleus muscle subjected to vibration

When vibration is applied to a muscle, the discharges of its motor units (MUs) become correlated with vibratory pulses. This effect has been extensively studied by single MU recording techniques. We suggested the surface EMG to be useful in this context to reveal a generalized pattern of MU firing. The surface EMG of human soleus muscle subjected to vibration during a voluntary contraction was recorded with precautions to suppress vibratory artifacts. Spectral analysis of the EMG and of the rectified EMG (REMG) revealed characteristic peaks, present in the power spectra at the vibration frequency (VF) and its harmonics. Vibratory artifacts were negligible, since during the ischemic block of the muscle, the peaks disappeared similar to the T-reflex extinction. If the VF was low compared with the major frequency domain of the EMG, the peaks were better expressed in the spectra of the REMG, while at higher VFs they were more pronounced in the EMG spectra. With the increase in the force of muscle contraction, the peaks, normalized to the total power of the spectrum, diminished. During a prolonged contraction in the presence of vibration, the peaks augmented, probably due to synaptic potentiation. Mathematical modeling of the surface EMG was performed to interpret the experimental data. The simulated patterns were consistent with the experimental results. Since the model predicted an increase in the normalized peaks with increasing number of MUs, it was suggested that at larger forces of contraction the correlation of MU discharges with the vibratory stimuli, on average, deteriorated.

Comparison of different estimators of electromyographic spectral shifts during work when applied on short test contractions

EMG was recorded during short test contractions performed during occupational work. Mean power frequency (MPF) and median frequency (MF), calculated from EMG spectra, and zero crossing rate (ZC) of the EMG signal were compared as estimators of local muscular fatigue. The results show that there is a systematic difference between the three estimates. The difference can be explained by dividing the effect of muscle fatigue on EMG spectra into a motor unit action potential velocity effect and a firing statistics effect. Furthermore, it is shown that the phenomenon of increasing estimators of EMG spectrum shift is unlikely to be caused by motor unit action potential velocity increase. Successive recruitment of new motor units is suggested as a feasible explanation.

こう筋筋疲労過程における筋電位伝導速度および周波数パラメータの観察 ＩＩ 周波数パラメータについて

During sustained isometric contraction of the jaw muscles, muscular fatigue causes a shift towards lower frequencies in the EMG frequency power spectrum. This shift is due to a reduction of myoelectric conduction velocity. The purpose of this study was to investigate the effect of surface electrode location on the estimates of frequency components, and to determine the appropriate frequency parameters of surface EMG which provided the best fit when comparing conduction velocity. Studies were performed in the masseter muscles of 8 healthy subjects. The myoelectric potentials were derived using 12 differential amplifiers from electrode arrays. The frequency parameters calculated were as follows: peak frequency, mean power frequency, cumulative power function (10, 25, 50 and 75%), median frequency ratio, low frequency ratio and measure H. As the results, following findings were obtained: 1. The high frequency content occurred at the region of end-plate zone and tendonous insertion of the muscle. 2. EMG spectra obtained during fatigue were shifted to lower frequencies for all regions except adjacent end-plate zone. 3. The relationships between conduction velocity and frequency parameters during fatiguing contractions were almost linear except peak frequency. 4. It was concluded that the location between distal end-plate and the tendon was "stable" zone for studying muscular fatigue.

Electromyographic activity during shivering of muscles acting at the human elbow

1. 1.|Surface electromyograms have been recorded from biceps and triceps brachii during cold induced shivering in normal human subjects. 2. 2.|Biceps was commonly found to be co-contracting with triceps when the shivering subject was voluntarily producing an extension force at the elbow; when the subject was warm only triceps contracted. 3. 3.|During shivering the EMG spectra of both biceps and triceps normally showed a pronounced peak in the range 7–12 Hz. The cross-spectrum of the EMGs for the two muscles showed a similar peak, with their linked activity organised reciprocally (i.e. approximately 180 out of phase).

Differential effects of changes in mechanical limb properties on physiological and pathological tremor.

The effect of changes in mechanical limb properties on the peak frequency of different tremor forms was analysed. Wrist tremor was recorded by an accelerometer fixed to the dorsum of the hand and demodulated surface EMG was recorded from the wrist extensors, while the extended hand was loaded with successively heavier weights. Physiological tremor was characterised by flat EMG spectra and a gradual decrease in tremor peak frequency with increasing load, as would be expected from the properties of a passive spring-mass-system. Also the peak frequency of activated physiological tremor characterised by increased synchronisation between motor units decreased in frequency with increasing loads. EMG spectra showed clear peaks of activity at the various mechanically determined tremor frequencies. In contrast, in two pathological tremor forms, the postural tremor in Parkinsonian patients and essential tremor, peak frequency tended to remain stable irrespective of changes in load. The method therefore allows a simple distinction between physiological and these two pathological tremors.

Lower-lip EMG and displacement during bilabial disfluencies in adult stutterers.

The purpose of this study was to describe the temporal patterns and spectral characteristics of antagonist lip muscle EMG and lip displacement during bilabial disfluencies in adult stutterers. Selective EMG recordings were obtained in five adult stutterers of mentalis and depressor labii inferior motor units (MENT and DLI) that were activated in a reciprocal manner during fluent speech. During disfluencies (N = 91) these same motor units were activated primarily in a reciprocal manner or DLI was not activated. These findings are not consistent with previous reports that stutterers' disfluencies involve cocontraction and overall increases in the activation levels of antagonist muscles. Spectral analysis of bilabial disfluencies revealed peaks at 5-9 Hz in the MENT EMG spectra of the five subjects and at 5-6 Hz in the displacement spectra of two subjects. A refinement in the classification of stutterers' disfluencies is suggested on the basis of individual differences in lip EMG and displacement spectra, and the mechanisms of stuttering tremor are discussed.

A new technique for measuring muscle fiber conduction velocities in full interference patterns

The motor unit potential shape, mainly its duration and frequency spectra, and the EMG IP crispiness and its frequency spectra are affected by the muscle fiber conduction velocities (MFCVs). Present techniques are somewhat deficient in that they are not adaptable to measure MFCVs continuously and intramuscularly in the presence of interference patterns, and to do so without interfering with the ongoing muscular activity. In this study a cross-correlation with averaging correlograms technique is presented. An EMG needle electrode, with two recording surfaces 1 cm apart, continuously record two channels of EMG activity which is analog-to-digital converted. Contiguous segments of the signals are cross-correlated, the evolved correlograms are averaged together, averaging-out the time-unlocked noise, and averaging-in a peak that represent the average time it takes the EMG signal to propagate from one recording surface to the other. From the distance between these two recording surfaces and the above calculated propagation time the MFCVs can be computed and monitored intramuscularly either in weak or in strong, in isometric or isotonic contractions. But for the fact that a needle is introduced, there is no interference with the muscle electrical activity. It is expected that this technique may add to EMG diagnosis of neuromuscular disorders, will be used to monitor muscular fatigue and applied in normalizing EMG spectra, conditioning them for a better use in diagnostic electromyography.

Electromyographic power spectral changes associated with the sleep-awake cycle and with diazepam treatment in the rat

Power spectral analysis was used to study temporalis muscle EMG activities during the sleep-awake cycle in the rat. EMG spectra derived from EMG during the states of slow-wave sleep. REM sleep and wakefulness demonstrated qualitative and quantitative differences. Diazepam treatment produced reductions in EMG spectral power during wakefulness. Thus, our experimental model allows qualitative and quantitative delineation of EMG activity associated with behavioral changes or drug treatments.