Motor unit potential contribution to surface electromyography

The background of the bioelectric activity of muscle recorded from the surface of the skin (surface electromyography) in terms of the representation of single motor units of the underlying muscle(s) is not very well documented or understood. An insight into the composition of an electromyogram is essential for the proper interpretation of one of the most widely applied electrophysiological techniques. In the present paper, a study of the contribution of single motor unit potentials to the surface electromyogram is presented. To this end, the decline of different components of the motor unit potential with depth of the motor unit is quantified. Experimentally, the action potentials from motor units at several positions in the muscle were recorded by 30 skin surface electrodes. Simultaneous use of scanning electromyography provided information about the actual position and size of the motor unit. Observed linear log–log relationships between motor unit potential magnitudes and distance indicated the usefulness of a power function to describe the motor unit potential's dependence on recording distance. It is shown that different specific surface motor unit potential characteristics fall off differently with depth. The magnitude–distance relationship is shown to be dependent on the recording configuration (unipolar vs. bipolar recording, including the inter-electrode distance) and the chosen motor unit potential parameter (negative peak amplitude, positive peak amplitude and area).     

Pelvic floor neuropathy in relation to the outcome of burch colposuspension

The aim of the study was to determine the role of neurogenic damage to pelvic floor muscles on the outcome of Burch colposuspension. Thirty women objectively continent after Burch colposuspension and 18 women with recurrent stress urinary incontinence (RSUI) were investigated with concentric needle electrode electromyography (EMG) in both pubococcygeus muscles and the external anal sphincter muscle. Neurogenic EMG patterns were significantly more often seen in the pubococcygeus muscles in women with RSUI than in women continent after the colposuspension (P<0.05). The distribution of neurogenic EMG patterns in the investigated muscles was significantly more pronounced in women with RSUI than in continent women: at least one pubococcygeus muscle with neurogenic EMG pattern, 72% vs. 34% (P<0.05); both pubococcygeus muscles, 50% vs. 13% (P<0.05); and all three investigated muscles 41% vs. 10% (P<0.05). In conclusion, the results imply an association between the outcome of the Burch colposuspension and the occurrence of neuropathy in the pelvic floor muscles. Occurrence of neurogenic damage in the pubococcygeus muscles seems to impair the outcome of Burch colposuspension.     

Shoulder strain in keyboard workers and its alleviation by arm supports

Summary Keyboard work consists mostly of dynamic contractions of the small muscles of the forearms and hands. This is accompanied by continuous activity in the arm, shoulder and neck muscles keeping the head and hand in the correct position. Eliminating the weight from the arm by means of support and the position of the arms influences the electrical activity of shoulder muscles when working at a keyboard. We studied the influence of elbow angle, as well as that of different arm supports, on electrical activity of upper trapezius muscle during keyboard work in healthy workers and persons suffering from shoulder pains. The measurements were carried out in the laboratory. EMG activities, which where measured as mean square root (RMS)-values at every 100-millisecond period in trapezius muscle when working, were lower, the greater the elbow angle. Furthermore electrical activity decreased when subjects used arm supports while working. It is evident that the static load to shoulder muscles can be lowered significantly in keyboard work, when the forearms are at an angle of at least 100 degrees and by using arm supports. The most convienient and ergonomic working position can also be found individually be the method used here.     

Surface EMG in the recording of fasciculations.

The usefulness of multichannel surface recording of fasciculations was evaluated by a retrospective study of 116 patients with various neurological disorders. Eight channels of a conventional electroencephalograph were used with plate electrode recordings from the upper arms and legs. Wide-spread fasciculations (defined as five or more of the eight muscle groups) were recorded in 48 of 54 patients with motor neuron disease, spinal muscular atrophy or postpolio syndrome, but noted on routine clinical examination at presentation in only 6. Eleven of 23 patients with peripheral neuropathy or myelopathy had fasciculations in five or more leads compared to one clinically, and 3 of 39 with other neurological diseases had fasciculations electrically but in only one were they clinically observed. The method is a noninvasive and sensitive adjunct to clinical examination for detecting fasciculations. Its diagnostic value is limited by the relatively high incidence of fasciculations in neuropathies and myelopathies. However, this study suggests that "false negatives" are rare and that the diagnosis of motor neuron disease should be reconsidered when less than five leads shows fasciculations.     

Anger Management Style and Hostility: Predicting Symptom-Specific Physiological Reactivity Among Chronic Low Back Pain Patients

It was hypothesized that anger management style (anger-in or anger-out) and hostility affect the aggravation of chronic low back pain (CLBP) through symptom-specific (i.e., lower paraspinal muscle) reactivity during stress. Subjects were 102 CLBP patients who performed mental arithmetic and an Anger Recall Interview (ARI) while trapezius and lower paraspinal EMG, SBP, DBP, and HR were recorded. Results showed anger-in × hostility and anger-out × gender interactions for lower paraspinal but not trapezius reactivity, and only during the ARI. Further analyses revealed that (1) hostility was related positively to lower paraspinal reactivity among high anger suppressors, (2) hostility was related negatively to lower paraspinal reactivity among low anger suppressors, and (3) anger expression was related positively to lower paraspinal reactivity only among men. Anger management style and hostility may contribute to the exacerbation of CLBP by influencing stress reactivity only in muscles near the site of pain or injury.     

Facial Muscle Tonus During REM and NREM Sleep

Equipment and procedures were devised for quantifying relatively noise-free recordings of low amplitude chin and lip electromyograms (EMGs) during sleep. A total of 28 REM periods were recorded from 5 young adult female Ss. Tonic EMG levels tended to decline toward their lowest level of the night beginning 5 min in advance of REM periods. With very rare exceptions, the lowest EMG levels of the night were maintained throughout REM sleep. During the 20 min of NREM sleep which followed REM periods, mean EMG levels increased over the REM levels but were lower than those recorded during the 20 min of NREM sleep which preceded the REM periods. This pattern of tonic EMG variation obtained for each of the first 3 REM periods of the night.     

位图在动态绘制肌电信号中的应用

鉴于常见的动态绘制肌电曲线时出现的屏幕闪烁和抖动问题 ,设计了在面向对象的VisualC 6 .0开发平台上 ,利用MFC(MicrosoftFoundationClasses)类库中的位图类CBitmap来绘制肌电曲线图像 ,解决肌电数据的动态回放和实时监测中的屏幕闪烁和抖动问题     

Adaptive spatial filtering of multichannel surface electromyogram signals

Spatial filtering of surface electromyography (EMG) signal can be used to enhance single motor unit action potentials (MUAPs). Traditional spatial filters for surface EMG do not take into consideration that some electrodes could have poor skin contact. In contrast to the traditional a priori defined filters, this study introduces an adaptive spatial filtering method that adapts to the signal characteristics. The adaptive filter, the maximum kurtosis filter (MKF), was obtained by using the linear combination of surrounding channels that maximises kurtosis. The MKF and conventional filters were applied to simulated EMG signals and to real EMG signals recorded with an electrode grid to evaluate their performance in detecting single motor units. The MKF was compared with conventional spatial filtering methods. Simulated signals, with different levels of spatially correlated noise, were used for comparison. The influence of one electrode with poor skin contact was also investigated. The MKF was found to be considerably better at enhancing a single MUAP than conventional methods for all levels of spatial correlation of the noise. For a spatial correlation of 0.97 of the noise, the improvement in the signal-to-noise ratio, where a MUAP could be detected, was at least 6 dB. With a simulated poor skin contact for one electrode, the improvement over the other methods was at least 19 dB.     

Dynamic relationship between EMG and torque at the human ankle: Variation with contraction level and modulation

Stochastic system identification techniques were used to determine the dynamic relationship between the electromyogram (EMG) and torque in the ankle muscles of normal human subjects. EMG and torque were recorded while subjects modulated ankle torque by tracking a computer-generated stochastic waveform. Nonparametric impulse response functions (IRFs) relating EMG to ankle torque were computed and parameterised by determining the parameters of the second-order system which provided the best least-squares fit. Two sets of experiments were carried out. In the first, the mean level of torque was varied from 5 per cent of the maximum voluntary contraction (MVC) to 30 per cent MVC while the depth of modulation was held constant at ±5 per cent of MVC. In the second series of experiments the mean torque was held constant at 25 per cent MVC while the depth of modulation was varied from ±2.5 per cent to ±25 per cent. The major findings were: (1) A second-order, low-pass filter provided a good quasilinear model of the EMG/force dynamics under all conditions; (2) The model parameters depended only weakly on the mean level of torque; (3) In contrast, the model parameters depended strongly on the amplitude with which the contraction was modulated; the natural frequency increased significantly with the depth of modulation.     

EMG patterns in antagonist muscles during isometric contraction in man: Relations to response dynamics

Summary We studied the EMG activity of biceps and triceps in human subjects during isometric force adjustments at the elbow. Rapid targeted force pulses exhibited stereotyped trajectories in which peak force was a linear function of the derivatives of force and the time to peak force was largely independent of its amplitude. These responses were associated with an alternating triphasic pattern of EMG bursts in agonist and antagonist muscles similar to that previously described for rapid limb movements. When the instructions demanded rapid force pulses, initial agonist bursts were of constant duration, and their magnitude was strongly related to peak force achieved. The timing of EMG bursts in antagonist pairs was closely coupled to the dynamics of the force trajectory, and the rising phase of the force was determined by both agonist and antagonist bursts. When peak force was kept constant and rise time systematically varied, the presence and magnitude of antagonist and late agonist bursts were dependent on the rate of rise of force, appearing at a threshold value and then increasing in proportion to this parameter. It is proposed that antagonist activity compensates for nonlinearity in muscle properties to enable the linear scaling of targeted forces which characterizes performance in this task.Supported by the Dystonia Medical Research Foundation and NS 19205