The influence of electrode position on bipolar surface electromyogram recordings of the upper trapezius muscle

Summary The effect of electrode position on the upper trapezius muscle on the myo-electric signal amplitude was investigated with special reference to arm position and estimate of force output. Previously, a depression of the electromyogram (EMG) signal has been reported midway between the seventh cervical vertebrae (C7) and acromion (Veiersted 1991, Eur J Appl Physiol 62:91–98) although this electrode position has been recommended (Zipp 1982, Eur J Appl Physiol 50:41–54). Ten healthy subjects performed maximal shoulder elevations with the arm in vertical, abducted and flexed positions and they performed a dynamic movement test. The myo-electric signal was recorded along the length of the right upper trapezius muscle by a 16-channel bipolar array electrode and was integrated with a 0.2-s time resolution. A region just lateral to the midpoint between C7 and the lateral edge of acromion was found with high and stable amplitudes (% coefficient of variation equalled 5.6). At the midpoint a dip in the amplitude profile appeared which was slightly displaced by arm abduction or flexion probably due to sliding, of the skin relative to the muscle. A linear EMG-force relationship was found in the region with high signal amplitudes, whereas the more lateral and the dip region showed highly variable EMG-force relationships. Thus, it was found that when using bipolar surface electrodes with an interelectrode distance of 2 cm a centre position 2 cm lateral to the midpoint between C7 and acromion provided good repeatability and high signal yield.     

Ag/AgCl electrode assembly for thin smooth muscle electromyography

An electrode assembly for in vivo recording of the electrical activities of thin muscular layers is described. It comprises an active electrode surrounded by a ring, which avoids the recording of interfering signals. An improved technique for chlorinating the silver electrodes is presented: a partial electrolytic removal of an initial thick deposit is performed. This decreases the impedance, and lowers the ageing degradation of the electrodes in vivo. Recordings of extremely low frequency signals are allowed, whereas standard Ag/AgCl electrodes are inefficient when recording signals in the frequency domain under 0·1 Hz. The technical features which are described can be adapted to any Ag/AgCl electrode developed for in vivo measurements.     

The reproducibility of test contractions for calibration of electromyographic measurements

Summary The main purpose of this study was to evaluate the reproducibility of electromyographic (EMG) measurements and specifically to test a calibration procedure with submaximal test contractions. Bipolar surface electrodes (20 mm fixed distance) were repositioned by a tracing sheet on both trapezius muscles, halfway between acromion and processus prominens. Submaximal test contractions were performed by keeping both arms straight abducted 90° and forward flexed 10° for 15-s periods. The arm position could be precisely reproduced in the frontal plane, but deviated forwards by 4° in the horizontal plane, where the sensitivity of the EMG response to arm position was lowest. The electrodes were repositioned within a radius of 3 mm with a probability of 90%. Large deviations in the EMG response were found within this radius and a significant depression of the EMG response was recorded over the middle part of the muscle (the innervation zone?). This change in sensitivity of the EMG response with electrode position occurred in parallel for the test and maximal contractions. The total coefficient of variation was estimated to be 23% for recurrent EMG measurements using the calibration procedure described.     

Application of a modified two-point backward difference to sequential event detection in surface electromyography

Reliable detection of onset and termination of muscle contraction is an essential task in the analysis of surface electromyographic signals. An event detection method that can be used for sequential detection of both onset and termination of muscle contraction is described. The method builds on the techniques of envelope detection, two-point backward difference and threshold based decision making. Therefore, fast conventional digital signal processing techniques can be used in its implementation. Because the method is computationally efficient, it can be employed in both real-time and non-real-time applications. This text discusses the architecture of the method, considers the practical aspects of its implementation, analyses its computational complexity and evaluates its performance on the grounds of experimental results.     

Electro-mechanical stability of surface EMG sensors

This study compared the performance of surface electromyographic (sEMG) sensors for different detection conditions affecting the electro-mechanical stability between the sensor and its contact with the skin. These comparisons were made to gain a better understanding of how specific characteristics of sensor design and use may alter the ability of sEMG sensors to detect signals with high fidelity under conditions of vigorous activity. The first part of the study investigated the effect of different detection surface contours and adhesive tapes on the ability of the sensor to remain in electrical contact with the skin. The second part of the study investigated the effects of different skin preparations and hydrophilic gels on the production of movement artifact resulting from sinusoidal and impact mechanical perturbations. Both parts of the study evaluated sensor performance under dry skin and wet skin (from perspiration) conditions. We found that contouring the detection surface and adding a more adhesive double-sided tape were effective in increasing the forces needed to disrupt the electrical contact between the electrodes and the skin for both dry skin and wet skin conditions. The mechanical perturbation tests demonstrated that hydrophilic gel applied to the detection surface of the sensor produced greater movement artifacts compared to sensors without gel, particularly when the sensors were tested under conditions in which perspiration was present on the skin. The use of a surfactant skin preparation did not influence the amount of movement artifacts that resulted from either the sinusoidal or impact perturbations. The importance of these findings is discussed in terms of their implications for improving sEMG signal fidelity through sensor design modifications and procedures for interfacing them with the skin.     

Monopolar surface electromyography: a better tool to assess motoneuron excitability upon passive muscle stretching

Bipolar and monopolar surface electromyography (sEMG) are known procedures to measure the H-reflex. However, signal cancellation is a potential experimental problem of bipolar sEMG. The results of our study show that monopolar sEMG was the more sensitive procedure to differentiate motoneuron excitability at different passive muscle stretching speeds as it overcame signal cancellation.     

Amplitude and frequency measures of surface electromyography during dual task elbow torque production

Summary Studies of motor unit recruitment thresholds have demonstrated the existence of task-specific motor units within the muscles controlling the elbow. Two degree-of-freedom (df) task specificity was investigated at higher levels of elbow torque using the amplitude and frequency characteristics of surface electromyography (EMG). Flexion and supination torque data were collected together with EMG from electrode pairs on the brachioradialis (BRAD), biceps brachii short head, and medial and lateral aspects of biceps brachii long head, while subjects (n=14) performed the following four combinations of isometric tasks: (1) maximum voluntary contraction (MVC) flexion (F) and (2) MVC supination (S), each with a targeted torque of zero in the second d f; (3) MVC flexion with targeted MVC supination (FS); and (4) MVC supination with targeted MVC flexion (SF). Median power frequency (MEDF) and root mean square (RMS) amplitude under steady-state torque conditions were calculated and analyzed using ANCOVA models with planned contrasts (=0.05). A significant main effect for task was found in RMS, but not in MEDF. Contrasts showed a significant increase in RMS response in the dual MVC tasks (FS and SF) over the single MVC tasks of F and S. The lack of frequency changes with alterations in RMS data indicates that the underlying recruitment/rate coding scheme in use for dual-d f tasks may be different than in single-d f tasks, and provides possible support for the notion of motor unit task groups. Task-by-site interactions were found for both MEDF and RMS, and illustrated that the three biceps sites differed from BRAD in their responses to the F versus S tasks. These results provide further support that the synergy between biceps and BRAD is not fixed, and that the concept of flexor equivalence at the elbow does not hold under all torque task conditions     

Effects of electrode dislocation on electromyographic activity and relative rest time: Effectiveness of compensation by a normalisation procedure

Myofeedback seems a promising technique to treat myalgia related to computer work. A garment with embedded electrodes allows independent use by the subject. However, this inevitably results in electrode dislocations that can cause such variability in the electromyogram (EMG) parameters that the treatment fails. The objective was to investigate the variability introduced by electrode displacement on EMG root mean square (RMS) and relative rest time (RRT) and the effect of a normalisation procedure using a reference contraction to compensate for this. Dislocation was simulated using simultaneous recordings of pairs of electrodes situated 15 mm apart on the trapezius muscle, surrounding a central electrode pair at the standard position. To assess sensitivity for electrode displacement, intra-subject variability was used. To assess the effects of normalisation, both intra and inter-subject variability were used. Results indicated a large sensitivity of RMS to electrode displacements, with no differences between typing (42%) and the reference task (43%). No systematic changes were found relative to a specific electrode dislocation. Normalisation of RMS resulted in a decrease in the sensitivity for electrode displacement (33%), but did not decrease inter-subject variability (27%). The median value of the intra-subject variability of RRT, using a fixed threshold, was 4.9%, whereas the normalised threshold did not decrease the intra-subject variability (7%). The results suggest that RRT is suitable for individual follow-up measurements and applications such as myofeedback, without the need for a normalisation procedure. The use of RMS requires considerably more care, owing to its large sensitivity to electrode displacement and lack of substantial effects of normalisation.     

Recommendations for the standardization of growth hormone assays

The diagnosis of growth hormone (GH) deficiency is based on the GH biological response to pharmacological stimulation tests. The cut-off value defining normality is the same whatever the GH assay used. In a group of the French Society for Clinical Biology (SFBC), we have evaluated whether differences between the GH concentrations obtained with the 9 commercial GH assays available in France exist or not. The study samples consisted of 72 serum pools and serial dilutions of the recombinant GH 22 kDa international standard, IS 98/574. These dilutions were performed by using 3 different diluents: the specific diluent provided by the manufacturers and thus different from one assay to another, serum without GH and heparin plasma without GH. Despite being calibrated against the same international standard, the different assays proposed variable conversion factors between microg and mIU, and we decided to express the results in mIU. The GH concentrations obtained for the 72 serum pools with the 9 assays were highly correlated, but absolute concentrations were significantly different from one assay to another. In particular, the ratio between the concentrations measured with both assays giving the lowest and highest concentration in the same sample respectively was about 50%. In the recovery test executed by adding the international standard, the slope of the regression curve describing the relationship between expected and measured concentrations was different of 1 in all but one assay. Furthermore, for a given assay and a given expected concentration, the measured values were sometimes different by up to 30% depending on the diluent used. These results led us to advise the manufacturers to calibrate their assays against the recombinant GH international standard, IS 98/574, to take into account the matrix effect detected in our study and to use the official conversion factor of 3 mIU/microg. Waiting for this new calibration, it is recommended that the results should be expressed in mIU/L and that serum samples should be used for the measurement of GH instead of plasma samples.     

静态姿势下均匀负重和非负重时躯干和表面肌电活动

目的观察躯干均匀负重和非负重状态下静态前屈和后伸时腰背部、腹部及臀中肌的肌电活动规律和运动学特征。方法 6位正常健康的男性受试者直腿站立于特殊设计的试验框架和平台内做静态前屈和后伸的负重和非负重动作,每次试验持续4 s,重复3次。动作时,记录双侧腰臀部的10块肌肉:腹直肌、腹外斜肌、竖脊肌、多裂肌、臀中肌的肌电活动,以及三维角度运动轨迹和足底力系。计算标准化肌电、腰部躯干角和足底中心压力的位移。将所得数据作常规的统计分析。结果负重和非负重前屈时,都是背侧肌活动较大(10.47～16.94)。非负重后伸时,腹侧肌活动也较大;负重后,背侧肌(3.70～17.95)和臀中肌(6.64～11.52)活动增加,腹肌活动减少(10.66～4.18)。后伸时,躯干的闪动次数随负重增加而增多,在3D角上增加1.55次;负重后,足底中心压力向前后的移动多于侧方移动,前屈的前后方移动(14.60)多于后伸的移动(7.65)。结论后伸状态增加了背侧肌的活动,而且多裂肌更明显;同时,腰部角位移度和闪动次数增加,特别在后伸提重时更为显著。     

肌力训练对脑卒中恢复期偏瘫患者大腿表面肌电的影响

目的 探讨脑卒中恢复期偏瘫患者肌力训练对大腿肌群表面肌电(sEMG)信号特征的影响,为脑卒中患者的康复治疗提供客观依据.方法 共选取35例脑卒中恢复期偏瘫患者,分为治疗组(n=19)和对照组(n=16),治疗组给予6周的肌力训练,并在治疗前后在患侧膝关节屈伸最大等长收缩(MIVC)时记录股内侧肌、股直肌、股外侧肌、股二头肌、半腱半膜肌的sEMG信号,计算膝关节屈伸力矩值、均方根值(RMS)及其相应协同收缩率;对照组不给予康复训练,仅与治疗组同时进行上述指标测量.结果 治疗组治疗后患者患侧屈膝及伸膝MIVC力矩均较治疗前明显改善[屈膝:(18.02±6.52)nm比(13.12±5.79)nm,伸膝:(45.72±17.21)nm比(34.76±17.19)nm,均P＜0.05],而伸屈膝协同收缩率较治疗前无明显变化.对照组伸屈膝MIVC力矩和协同收缩率治疗前后差异则无统计学意义(均P＞0.05).治疗组治疗后患者患侧大腿股直肌、股外侧肌、半腱半膜肌作为主动肌时的RMS值均较治疗前明显改善[(146.60±60.85)μV比(97.02±57.17)μV,(172.65±60.73)μV比(131.46±52.15)μV,(188.69±89.60)μV比(130.57±73.76)μV,均P＜0.05],而股内侧肌、股二头肌的RMS值在治疗前后无明显变化,对照组治疗前后各肌的RMS值则无变化(均P＞0.05).结论 肌力训练可改善脑卒中恢复期偏瘫患者下肢屈伸肌力,但并不会增强下肢伸屈肌的异常收缩.sEMG结合力矩测量能更全面评估偏瘫肢体功能状态.     

基于表面肌电信号和动作捕捉的上肢运动疲劳分析EI北大核心CSCD

目前,上肢运动的疲劳状态监测,一般单纯依赖表面肌电信号(sEMG)对疲劳进行识别和分类,导致结果不稳定,存在一定局限。为此,本文将sEMG信号识别与动作捕捉技术引入到疲劳状态监测过程中,提出了一种融合改进的肌电疲劳阈值算法与生物力学分析的疲劳分析方法。本研究通过右上肢负载屈肘试验,同步采集肱二头肌sEMG信号与上肢动作捕捉数据,并同时运用柏格(Borg)疲劳度主观自觉量表记录受试者疲劳感受。然后,将融合改进的肌电疲劳阈值算法和生物力学分析的疲劳分析方法与平均功率频率(MPF)、谱矩比(SMR)、模糊近似熵(fApEn)、Lempel-Ziv复杂度(LZC)四种单一评价指标疲劳评价方法的试验结果进行对比。试验结果表明,本文方法对总体疲劳状态识别率结果达到98.6%,对轻松、过渡、疲劳三种状态的识别率分别达到97%、100%、99%,较其他方法更有优势。本文研究结果证明,本文方法在上肢运动过程中能够有效预防过度训练引起的二次损伤,对于疲劳监护具有重要意义。     

Recommendations for improved standardization of immunohistochemistry.

Immunohistochemistry (IHC) continues to suffer from variable consistency, poor reproducibility, quality assurance disparities, and the lack of standardization resulting in poor concordance, validation, and verification. This document lists the recommendations made by the Ad-Hoc Committee on Immunohistochemistry Standardization to address these deficiencies. Contributing factors were established to be underfixation and irregular fixation, use of nonformalin fixatives and ancillary fixation procedures divested from a deep and full understanding of the IHC assay parameters, minimal or absent IHC assay optimization and validation procedures, and lack of a standard system of interpretation and reporting. Definitions and detailed guidelines pertaining to these areas are provided.     

A simple,inexpensive 8-channel multiplexer for electromyography in human locomotion

Multichannel electromyographic studies of human locomotion can be greatly facilitated by the use of a multiplexer-demultiplexer system as described in this note. The system has 8-channel capability, each channel having a bandwidth from d.c. to 1800 Hz, and channel separation is at least 30 dB.     

Selective electromyography of dorsal neck muscles in humans

The patterns of activation of splenius capitis, semispinalis capitis, transversospinalis, and levator scapulae muscles were studied during various head-neck positions, movements, and isometric tests in 19 healthy human subjects. Myoelectric activities were recorded with intramuscular bipolar wire electrodes. Cervical computerized tomography of each subject was performed before the electromyography session in order to guide electrode insertion. Head motion was recorded using an electromechanical device. This report demonstrates that head motion results from a complex interaction of active muscular forces, passive ligamentous forces, and gravity. Splenius capitis has two main functions, i.e., cervical extension and ipsilateral rotation. Semi spinalis capitis and the transversospinalis are mainly extensors, and levator scapilae acts primarily on the shoulder girdle. Splenius capitis, semispinalis capitis, and transversospinalis play a subordinate part in ipsilateral tilting. In addition, most subjects' semispinalis capitis were gradually recruited during ipsilateral rotation. No signal was detected from the transversospinalis during rotation tests.     

Microcirculation in the upper trapezius muscle during sustained shoulder load in healthy women an endurance study using percutaneous laser-Doppler flowmetry and surface electromyography

Microcirculation in the upper portion of the trapezius muscle was measured percutaneously in a group of 16 healthy women of different ages by continuous laser-Doppler flowmetry (LDF) in relation to electromyography (EMG) during an endurance test. During the measurements the subject kept her arms straight and elevated at 45° in the scapular plane and held a 1-kg load in each hand as long as possible. This was followed by rest with the arms hanging and carrying no load. The 10-min recording period comprised 1-min initial rest followed by the endurance test and then recovery. Signal processing was done by computer on line. The LDF and root-mean-square (rms) EMG signals were normalized. Spectrum analyses of EMG mean power frequency (MPF) were performed. The amount of load produced was on average 2,267 (SD 939) N · m · s, i.e. shoulder torque × time expressed as Newton meter seconds, and the endurance time was 4.3 (SD 1.20) min. The rms-EMG as well as the LDF increased significantly during endurance, both when related to endurance time and to amount of load. The MPF showed no significant changes. The mean total increase in muscle blood flow was 175% of that recorded in the initial rest period. The average increase per each 10 s of contraction was 2.9%. Maximum was reached during the 1st min of recovery followed by a fall to the base level that was reached within 77 s on average. The amount of load produced and the blood flow increase was smaller than that found in a separate study of men, indicating a lower functional capacity. This may be of importance for the development of neck-shoulder disability in women.     

多发性肌炎和皮肌炎33例肌电图与血清肌酶在病程中的演变

目的：探讨多发性肌炎和皮肌炎起病不同时间的肌电图与肌酶的演变规律。方法：对33例多发性肌炎和皮肌炎病人做了53例次肌电图与肌酶检测，根据起病肜式、病程分组分析检测结果。结果：多发性肌炎和皮肌炎患者的肌酸磷酸肌酶升高程度在急、亚急性起病者与慢性起病者之间的差异具有统计学意义(P(0．05)；肌电图在急性、亚急性起病者多表现为肌源性损害与神经源性损害并存．而在慢性起病者则多表现为单纯肌源性损害。结论：肌电图和肌酶能够较客观地反映肌肉炎性病变的急剧程度，埘疾病的临床转归具有一定的预示意义。     

术中肌电图监测在微创经椎间孔腰椎椎间融合术中的应用

目的探讨术中肌电图监测在微创经椎间孔腰椎椎间融合术中应用的可行性和临床疗效。方法 2008年2月~2009年10月对16例行微创经椎间孔腰椎椎间融合治疗的患者进行术中肌电图监测,共18个节段,66枚椎弓根螺钉。椎管减压和椎间植骨融合时应用自发肌电图监测,经皮置入椎弓根螺钉时应用电刺激诱发肌电图监测。患者术后均行CT检查螺钉位置。结果所有患者在减压过程中无异常肌电反应,2例在置入椎间融合器后出现间断性自发肌电活动。23枚螺钉﹙34.8%﹚在置入开路锥的过程中,相应的监测肌肉引出至少1次有意义的肌电活动。3枚攻丝尾部检测<10mA,取出调整后重新置入。术后均无新的神经并发症。术后CT提示上述3个椎弓根皮质骨内侧破裂和1枚穿破外侧皮质骨。结论术中EMG监测在微创TLIF中是一种监测神经根功能的有效手段。     

Reproducibility of computer measurement of maximal isometric strength and electromyography in sedentary middle-aged women

The objectives of this study were (i) to determine the reproducibility of computer measurements of isometric strength and related electromyography in several muscle groups in sedentary middle-aged women, (ii) to evaluate the effects of different digital signal averaging methods on the reproducibility, (iii) to determine the final test score to be preferred in terms of improved reproducibility of isometric strength measurements, and (iv) to evaluate potential advantages provided by the computer measurement. Fifteen subjects were measured three times within a 2-week period. The measurements consisted of recordings of maximal isometric strength and rate of force production during trunk extension and flexion, leg extension and dominant forearm flexion with simultaneous recordings of surface electromyography, except in the trunk flexors. The following four final test scores were determined for each trial: the maximum of the three scores, the mean of the two highest scores, the median of the three scores and the mean of the three scores. The scores for the strength measurement were generally more reproducible (coefficient of variation, CV, approximately 6% and intraclass correlation coefficient ICCC, approximately 0.90) than those of the other measurements (CV > 10%, ICCC 0.13–0.97). There was no obvious preference for any type of final test score or for the width of the averaging window in the computer analysis. For isometric strength the reproducibility of the computer measurements was comparable to that of the voltmeter assessments. Computer analysis seems to be a versatile method for determining parameters of neuromuscular performance with reasonable reproducibility.