模型生理参数对表面肌电信号影响的仿真研究

通过模型研究肌肉生理参数对表面肌电信号的影响。根据肌肉的形态结构和生理特征,从肌电信号的信号源-细胞内动作电位开始,仿真了单肌纤维动作电位,由此合成了运动单位动作电位,再利用运动单位的募集发放模型,进一步仿真了运动单位动作电位序列,并最终完成了对表面肌电信号的仿真。在此基础上研究了极化区域宽度、跨膜电流密度分布和肌肉组织各向异性3个重要的模型生理参数对表面肌电信号统计特征的影响,得到了一些有价值的结果。实验结果表明,仿真肌电信号能够有效表征肌肉电生理变化过程。     

Training effects on muscle fatigue in man

Summary Effects of 3 months training, on electrical and mechanical failures during fatigue, were studied in human adductor pollicis muscle. Eight subjects carried out a daily training program of 10 series of 20 fast (0.5 s) voluntary contractions, against a load equivalent to 30–40% of the muscle maximal force. Contractile properties in control and trained muscles are tested by delivering supramaximal electrical pulses (30 Hz) to the motor nerve, thereby triggering series of 60 1-s contractions separated by 1-s intervals. Training produces significant increase in tension development during a 30 Hz isometric tetanus (+13%;P<0.001). Concimitant rates of tension development and of relaxation are respectively augmented by +18% (P<0.001) and +12% (P<0.001). No significant change of surface muscle action potential (SAP) is observed after training. The considerable loss of force recorded during fatigue in control muscles (–36%) is significantly smaller (P<0.001) after training (–17%). Slowing of tension development and of tension relaxation, observed during fatigue in control muscles (respectively –47% and –79%) is smaller after training (respectively –28% and –65%). Analysis of electrical failure indicates that training significantly (P<0.01) reduces augmentation of muscle SAP duration and area recorded during fatigue. Comparison of time courses of mechanical and electrical failures in control and trained muscles, supports the idea that intracellular processes play the major role in tension decay associated with fatigue in human adductor pollicis muscle.This work was supported by the Fonds National de la Recherche Scientifique of Belgium and the Conseil de la Recherche of the University of Brussels     

Muscle sound and electromyogram spectrum analysis during exhausting contractions in man

Summary The changes in the soundmyogram (SMG) and electromyogram (EMG) frequency content during exhausting contractions at 20070, 40%, 60070 and 80% of the maximal voluntary contraction (MVC) were investigated by the spectral analysis of the SMG and EMG detected from the biceps brachii muscles of 13 healthy men The root mean squares (rms) of the two signals were also calculated. Throughout contraction the EMG rms always increased while this was true only at 20% MVC for the SMG. A marked decrease was detected at 60% and 80% MVC. With fatigue the EMG spectra presented a compression towards the lower frequencies at all exercise intensities. The SMG showed a more complex behaviour with a transient increase in its frequency content, followed by a continuous compression of the spectra, at 60% and 80% MVC, and a nearly stable frequency content at lower contraction intensities. This study suggested that different aspects of the changes in the motor unit's activation strategy at different levels of exhausting contractions can be monitored by SMG and EMG signals.     

Propagation velocity measurement: Autocorrelation technique applied to the electromyogram

Muscle fibre conduction velocity is an important measurement in electrophysiology, both in the research laboratory and in clinical practice. It is usually measured by placing electrodes spaced at known distances and estimating the transit time of the action potential. The problem, common to all methods, is the estimation of this time delay. Several measurement procedures, in the time and frequency domains, have been proposed. Time-domain strategies usually require two acquisition channels, whereas some frequency-domain methods can be implemented using a single one. The method described operates in the time domain, making use of the autocorrelation function of the difference signal obtained from two needle electrodes and only one acquisition channel. Experimental results were obtained from the electromyogram of two biceps muscles (two adult male subjects, nine records each) under voluntary contraction, yielding an average of 3.58 m s⁻¹ (SD=0.04 m s⁻¹) and 3.37 m s⁻¹ (SD=0.03 m s⁻¹), respectively. Several tests showed that the proposed method works properly with electromyogram records as short as 0.3 s.     

电极配置对MUAP检测影响的仿真研究

本研究采用模型的方法,研究了电极配置对运动单位动作电位检测的影响.根据肌肉的形态结构和生理特征,从细胞内动作电位开始,仿真了运动单位动作电位序列.在此基础上,研究了电极的配置对运动单位动作电位的波形和统计特征的影响.结果表明:尺寸较小的电极选择性较好;差分电极的选择性优于单电极,适当调整其电极间距离和角度,可提高检测质量.     

Respiratory muscle electromyogram and mouth pressure during isometric contraction

When extra-diaphragmatic muscles are activated progressively under approximately isometric conditions, we expect a corresponding increase in respiratory muscle output. Therefore, we examined relative recruitment shown as the latency to onset of EMG activity, and the relationship between mouth pressure and electromyogram activity of the neck accessory and transversus abdominis (TRANS) muscles during respiratory maneuvers against occlusion. Fine wire electrodes were inserted into the scalene (SCLN), sternocleidomastoid (STERNO), trapezius (TRAPZ) and TRANS in six awake, healthy subjects. Mouth pressure, raw and moving average EMG signals were recorded during gradual production of expiratory or inspiratory mouth pressure to maximum (MPmax) at FRC in the standing posture. Group mean linear regression lines of EMG activity versus mouth pressure were strongly significant for SCLN and TRANS, less for STERNO, and least for TRAPZ. The SCLN and STERNO showed EMG activities with low, and TRAPZ showed EMG activity only with high, mouth pressure. At 90% MPmax, TRAPZ was much less active compared with TRANS, SCLN, or STERNO. These results suggest that over a wide range of respiratory effort there is a significant difference in the relationship between mouth pressure and EMG activity in the accessory muscles, with differential recruitment of individual respiratory muscles.     

Changes induced by eccentric training on force-velocity relationships of the elbow flexor muscles

The aim of this study was to examine the effects of a short term eccentric training period on force-velocity relationships of the elbow flexor muscles. From a muscle model, the maximal shortening velocity V_O(x) and the af parameter which varies according to the curvature of the force-velocity relationship of the muscle were determined. Sixteen volunteer subjects divided into 2 groups participated in this study (Group Eccentric GE, n=8 . Group Control GC, n=8). The subjects performed, on an isokinetic ergometer, 2 maximal concentric elbow flexions at different angular velocities (60, 120, 180; 240, 300, 360 °s^–1) and held maximal and submaximal isometric actions at an elbow flexion angle of 90°. Under isometric conditions, myoelectrical activity (EMG) of the biceps was recorded and quantified as a RMS value. All tests were performed before and after training sessions. Training was conducted 3 times a week for 4 weeks by the GE, and included 6×5 eccentric actions with a load of 100% of 1 RM. After training and for the GE, the af parameter and V_o(x) increased significantly (p<0.05). These changes were accompanied by a significant increase (p<0.05) of the RMS value of the maximal isometric action. This evolution towards faster characteristics for the elbow flexor muscles after training could be partly due to nervous adaptation.     

Recovery of the human biceps electromyogram after heavy eccentric,concentric or isometric exercise

Summary Five men performed submaximal isometric, concentric or eccentric contractions until exhaustion with the left arm elbow flexors at respectively 50%, 40% and 40% of the prefatigued maximal voluntary contraction force (MVC). Subsequently, and at regular intervals, the surface electromyogram (EMG) during 30-s isometric test contractions at 40% of the prefatigued MVC and the muscle performance parameters (MVC and the endurance time of an isometric endurance test at 40% prefatigued MVC) were recorded. Large differences in the surface EMG response were found after isometric or concentric exercise on the one hand and eccentric exercise on the other. Eccentric exercise evoked in two of the three EMG parameters [the EMG amplitude (root mean square) and the rate of shift of the EMG mean power frequency (MPF)] the greatest (P<0.001) and longest lasting (up to 7 days) response. The EMG response after isometric or concentric exercise was smaller and of shorter duration (1–2 days). The third EMG parameter, the initial MPF, had already returned to its prefatigued value at the time of the first measurement, 0.75 h after exercise. The responses of EMG amplitude and of rate of MPF shift were similar to the responses observed in the muscle performance parameters (MVC and the endurance time). Complaints of muscle soreness were most frequent and severe after the eccentric contractions. Thus, eccentric exercise evoked the greatest and longest lasting response both in the surface EMG signal and in the muscle performance parameters.     

Time and frequency domain analysis of electromyogram and sound myogram in the elderly

The aim of this work was to evaluate the influence of the ageing process on the time and frequency domain properties of the surface electrical and mechanical activity of muscle. In 20 healthy elderly subjects (10 men and 10 women, age range 65–78 years) and in 20 young controls, during isometric contractions of the elbow flexors in the 20%–100% range of the maximal voluntary contraction (MVC), estimations were made of the root mean square (rms) and the mean frequency (MF) of the power density spectrum distribution, from the surface electromyogram (EMG) and sound myogram (0SMG) signals, detected at the belly of the biceps brachii muscle. Compared to the young controls, the MVC was lower in the elderly subjects (P < 0.05); at the same %MVC the rms and the MF of EMG and SMG were lower (P < 0.05) in elderly subjects; the rms and MF of the two signals increased as a function of the effort level in all groups. Only in the 80%–100% MVC range did the EMG-MF level off and the SMG-rms decrease; in contrast the young controls, at 80% MVC the high frequency peak in the SMG power spectrum density distribution was not present in the elderly subjects. The results for MVC and %MVC can be related to the reduction in the numbers of muscle fibres in aged subjects. In particular, the lack of fast twitch fibre motor units (MU), attaining high firing rates, might also explain the result at 80% MVC. In 80%–100% MVC range the two signals rms and MF behaviour may have been related to the end of the recruitment of larger MU with high conduction velocity, and to the further increment of MU firing rate in the biceps brachii muscle beyond 80% MVC, respectively. Thus, the coupled analysis of the EMG and SMG with force suggests that in the elderly subjects the reduction of the number of muscle fibres may have co-existed with a MU activation pattern similar to that of the young subjects.     

The influence of air temperature on the EMG/force relationship of the quadriceps

Summary Surface electromyography (EMG) in the past has been used to estimate the intensity of muscle contraction. These estimates were derived from the EMG/force relationship measured at room temperature. How the surface EMG signal is influenced by varying air temperature as it relates to the EMG/force relationship has yet to be investigated. Thus, this study evaluated the influence of different air temperatures (10, 23 and 40° C) on surface EMG during contractions of the quadriceps muscle. Ten subjects [mean (SD) age 29 (7) years and weight 78.3 (7.8) kg] performed a criterion task of five contractions ranging from 10 to 100% of a maximal voluntary contraction, five times over a 1.5-h period in all conditions. The EMG signals generated from the rectus femoris, and the forces associated with the contractions, were captured on FM tape and subsequently digitized at a sampling rate of 2000 Hz. The relationship between EMG and force was different under the different conditions; EMG was reduced at a given force as temperature increased, and the EMG increased in the 10° C environment over time. The differences that occurred at the various temperatures were believed to be related to fluid distribution in the muscle, muscle conduction velocity and sweating. The data imply that the EMG/force relationship measured using surface electrodes is influenced by ambient temperature.     

Experimental muscle pain changes motor control strategies in dynamic contractions

This study investigated the effect of muscle pain on muscle activation strategies during dynamic exercises. Ten healthy volunteers performed cyclic elbow flexion/extension movements at maximum speed for 2 min after injection of (1) hypertonic (painful) saline in the biceps brachii, (2) hypertonic saline in both biceps brachii and triceps brachii, and (3) isotonic (nonpainful) saline in the biceps brachii muscle. Surface electromyographic (EMG) signals were collected from the upper trapezius, biceps brachii, triceps brachii, and brachioradialis muscles (to estimate EMG amplitude) and with an electrode arrays from biceps brachii (to estimate muscle fiber conduction velocity [CV]). In all conditions, the acceleration of the movement decreased throughout the exercise, and kinematic parameters were not altered by pain. With respect to the control condition, pain induced a decrease of the biceps brachii (mean ± SE, –23±4%) and brachioradialis (–10±0.4%) integrated EMG (IEMG) in the beginning of the exercise, and an increase (45±3.5%) of the upper trapezius IEMG at all time points during the exercise. The biceps brachii IEMG decreased over time during the nonpainful exercises (–11±0.6%) while it remained constant in the painful condition. Biceps brachii CV decreased during painful conditions (–12.8±2.2%) while it remained constant during the nonpainful condition. In conclusion, muscle pain changes the motor control strategy to sustain the required dynamic task both in the relative contribution between synergistic muscles and in the motor unit activation within the painful muscle. Such a changed motor strategy may be highly relevant in models of occupational musculoskeletal pain conditions.     

Simultaneous estimation of muscle fibre conduction velocity and muscle fibre orientation using 2D multichannel surface electromyogram

The paper presents a new approach for simultaneous estimation of muscle fibre conduction velocity (MFCV) and muscle fibre orientation (MFO) for motor units (MUs) in two-dimensional (2D) multichannel surface electromyography recordings. This is an important tool for detecting changes and abnormalities in muscle function and structure. In addition, simultaneous estimation of MFO and MFCV avoids the necessity of manual electrode alignment. The proposed method detected propagating MU action potentials (MUAPs) in a running time window as moving components in amplitude maps. Thereafter, estimations were obtained by fitting a three-dimensional function to these maps. The performance was evaluated using synthetic MU signals at 10 dB SNR and authentic biceps brachii measurements. Results demonstrated MFCV and MFO estimates with standard deviations of less than 0.05 m s⁻¹ and 1° for simulated signals, and less than 0.2 m s⁻¹ and 4° for experimental data. However, standard deviations as low as 0.12 m s⁻¹ and 1.6° from real signals were demonstrated. It was concluded that the method performs as well as, or better than, linear array multichannel methods when individual propagating MUAPs can be identified, even if electrodes are not aligned with fibre direction.     

The influence of muscle pain and fatigue on the activity of synergistic muscles of the leg

The purpose of this study was to investigate the effect of experimentally induced muscle pain on the motor-control strategies of synergistic muscles during submaximal fatiguing isometric contractions. The root mean square (RMS) and median frequency (MF) of the surface electromyographic (EMG) signal from synergistic plantarflexors and dorsiflexors were assessed to exhaustion. Ten subjects performed sustained dorsiflexions and plantarflexions at two contraction levels, 50% and 80% of maximum voluntary contraction, with or without muscle pain, induced by injection of 6% hypertonic saline in one synergist. In the painful contractions, the RMS of the EMG signal was decreased compared to the control condition in the initial phase of the contraction, in the muscles where pain was induced as well as in the nonpainful synergists. Moreover, the EMG signal MF decreased faster during muscle pain than in the control condition. The endurance time was shorter during muscle pain, and some of the nonpainful synergists showed increased compensatory activity at the end of the contractions to maintain the target force. The decreased EMG activation during pain was coupled with significantly decreased torque levels during the painful condition that would partly explain the results. However, the ratio between force and EMG amplitude was decreased for both the painful and nonpainful synergists, so other mechanisms might explain the present findings. This study shows that localized muscle pain can reorganize the EMG activity of synergists where no pain is present. These findings may have implications for the understanding of manifestations seen in relation to painful musculoskeletal disorders.     

Changes in the action potential and contractile properties of skeletal muscle in human's with repetitive stimulation after long-term dry immersion

This paper compares the effects of 7-daydry immersion and intermittent muscle contraction on electrical and mechanical failure during muscle fatigue in the human triceps surae muscle electrically stimulated at 50 impulses·s⁻¹ via its motor nerve. Intermittent contractions of 60-s duration were separated by 1-s intervals for identical duration of tension development. The 60-s intermittent contractions decreased tetanic force to 57% (P<0.05) of initial values, but force reduction was not significantly different in the two fatigue tests: the fatigue index was 36.2 (SEM 5.4)% versus 38.6 (SEM 2.8)%, respectively (P>0.05). Whilst identical force reduction was present in the two fatigue tests, it would appear that concomitant electrical failure was considerably different. This electromechanical dissociation would suggest that a slowing of conduction along nerve and muscle membranes did not explain the observed mechanical failure. It is suggested that intracellular processes played major role in contractile failure during intermittent contractions after muscle disuse.     

Non-invasive method to detect motor unit contractile properties and conduction velocity in human vastus lateralis muscle

The contractile properties and conduction velocity of motor units are estimated by using surface array electrodes during voluntary isometric contractions of the human vastus lateralis muscle. The subjects develop and maintain sufficient force to steadily discharge a given motor unit, assisted by visual feedback from an oscilloscope. The torque curve developed around the knee joint is triggered by an individual motor unit and averaged. 31 motor units in five subects are studied. The twitch tension detected ranges from 3 to 27 m Nm with a mean of 12·3 m Nm. The threshold force ranges from 1·88 to 10·12 Nm with a mean of 5·48 Nm, which is 3% of the maximal voluntary contraction. The rise time ranges from 56 to 106 ms with a mean of 83 ms. The mean value of conduction velocity is 4·64 m s⁻¹. The twitch tension is positively correlated to the threshold force (r=0·839, p<0.01), but has no relation to the other parameters. It is concluded that the use of non-invasive surface array electrodes provides the contractile properties of motor units and muscle fibre conduction velocity during weak contractions.     

脑瘫尖足患儿站立和行走中下肢肌肉的表面肌电图

文题释义：表面肌电图(surface lectromyography,SEMG)：是分析相关肌肉功能状况的一种无创性检查手段,可以客观评定静止或运动时肌肉的活动情况。在控制良好的情况下,肌电信号活动的变化在很大程度上能够定量反映肌肉功能状态、肌张力、肌力水平、多肌群协调性等肌肉的变化,对肌肉功能状况提供客观指标,对于肌肉相关疾病的康复设计、康复治疗,特别是疗效评定有着不可替代的重要作用。 平均振幅：是用来描述一段时间内肌电幅值的平均变化特征。一般认为与运动单位募集程度和兴奋节律的同步化有关,它间接反映肌肉收缩力大小。一定范围内,平均振幅与肌肉收缩过程中参与工作运动单位数量呈正比,反映了肌肉收缩强度的变化。 背景：在控制良好的情况下,肌电信号活动的变化在很大程度上能够定量反映肌肉功能状态、肌张力、肌力水平、多肌群协调性等肌肉的变化,对肌肉功能状况提供客观指标。 目的：探讨脑瘫尖足患儿站立和行走中下肢肌肉的表面肌电图变化。 方法：应用美国NORAXON公司生产的 TELEMYO 2400R G2表面肌电图遥测仪对20例脑瘫单侧尖足患儿在静止站立、常态行走下进行双下肢胫前肌、腓肠肌内侧的表面肌电测试。比较受试者尖足侧与对侧肌肉的肌电活动。研究方案经过了上海瑞金医院伦理委员会批准,所有受试者及监护人均签署了“知情同意书”。 结果与结论：①受试者静止站立和常态行走时,其尖足侧腓肠肌内侧的平均肌电振幅、平均肌电积分均低于对侧(P < 0.05);②受试者静止站立和常态行走时,其尖足侧胫前肌和腓肠肌内侧的平均频率、中位频率均高于对侧(P < 0.05);③结果说明,脑瘫患儿尖足侧胫前肌、腓肠肌内侧存在表面肌电图信号异常,脑瘫单侧尖足患儿下肢肌肉活动不均衡,提示表面肌电图对脑瘫患儿神经肌肉系统功能状态的评价具有实用价值。 ORCID: 0000-0001-8732-8452(许萍);0000-0001-9909-3355(梁雷超) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Motor unit action potential rate and motor unit action potential shape properties in subjects with work-related chronic pain

The objective of this study was to investigate differences in motor control of the trapezius muscle in cases with work-related chronic pain, compared to healthy controls. Ten cases with chronic pain and 13 controls participated in the study. Electromyographic (EMG) signals were recorded from the upper trapezius during five computer work-related tasks. Motor control was assessed using global root-mean-square value (RMS_G), motor unit action potential (MUAP) rate (number of MUAPs per second, MR) and two MUAP shape parameters, i.e. root-mean-square (RMS_MUAP) and median frequency (FMED_MUAP). MR and FMED_MUAP were higher for the cases than for the controls (P<0.05). RMS_MUAP showed a trend for higher values in the chronic pain group (P<0.13), whereas RMS_G did not show a significant difference between the groups. The higher MR, FMED_MUAP and the trend for higher RMS_MUAP suggest that more high-threshold MUs contribute to low-level computer work-related tasks in chronic pain cases. Additionally, the results suggest that the input of the central nervous system to the muscle is higher in the cases with chronic pain.     

A simulation model of the surface EMG signal for analysis of muscle activity during the gait cycle

This work describes a model able to synthetize the surface EMG (electromyography) signal acquired from tibialis anterior and gastrocnemious medialis muscles during walking of asymptomatic adult subjects. The model assumes a muscle structure where the volume conductor is represented by multiple layers of anisotropic media. This model originates from analysis of the single fiber action potential characterized by the conduction velocity. The surface EMG of voluntary contraction is calculated by gathering motor unit action potentials estimated by the summation of all activities of muscle fibers assumed to have a uniformly parallel distribution. The parameters related to the gait cycle, such as onset and cessation timings of muscle activation, amplitude of muscle contraction, periods and sequences of motor units' recruitment, are included in the model presented. In addition, the relative positions of the electrodes during gait can also be specified in order to adapt the simulation to the different acquisition settings.