Low-level exertions of the neck musculature: a study of research methods.

Musculoskeletal neck discomfort is prevalent in many occupations and has been the focus of much research employing surface electromyography (sEMG). Significant differences in experimental methods among researchers make comparisons across studies difficult. The goal of the current research was to use empirical methods to answer specific methodological questions concerning use of sEMG in evaluation of the neck extensor system. This was accomplished in two studies. In Experiment 1, ultrasound technology was used to: (a) determine accessibility of m. splenius and semispinalis capitis with surface electrodes, (b) identify appropriate electrode locations for these muscles/muscle groups, and (c) illustrate potential benefits of using ultrasound in locating muscles/placing electrodes. Experiment 2 sought to assess effects of posture when normalizing sEMG data. Results from Experiment 1 showed no direct access to semispinalis capitis for surface electrodes; their activity can only be sampled as part of a group of muscles. In most subjects, m. splenius was found to be accessible to surface electrodes. Electrode placement recommendations are provided. Results of Experiment 2 showed significant differences in normalized EMG data between a posture-specific technique and a reference posture technique. Posture-specific normalization is recommended for accurately assessing the relative intensity of contractions of these muscles.     

慢性非特异性颈部不适飞行员与无症状飞行员之间头颈夹肌表面肌电特征的比较

目的:通过对慢性非特异性颈部不适飞行员与无症状飞行员之间头颈夹肌表面肌电特征的比较,为慢性非特异性颈部不适飞行员的早期诊断提供参考依据。方法:用表面肌电仪测量52名慢性非特异性颈部不适飞行员与11名无症状飞行员双侧头颈夹肌的松弛状态、等长收缩以及异长收缩时的表面肌电特征,分析不同状态下双侧头颈夹肌疲劳性肌电指标MFs、MPFs、ZCRs以及平均肌电AEMG值,用统计学软件SPSS 18.0分析实验结果。结果:非特异性颈部不适飞行员与无症状飞行员双侧头颈夹肌在松弛状态时疲劳性肌电指标MFs、MPFs、ZCRs比较均无统计学差异(P0.05),其双侧头颈夹肌在等长收缩和异长收缩时间有统计学差异(P0.05)。头颈夹肌处于松弛状态时,两组间平均肌电AEMG比较无统计学差异(P0.05),而在肌肉等长收缩和异长收缩时,两组间比较有统计学差异(P0.05)。结论:慢性非特异性颈部不适飞行员与无症状飞行员之间头颈夹肌表面肌电相关指标存在统计学差异,慢性颈部不适的飞行员相比无症状飞行员更易出现头颈夹肌的疲劳以及头颈夹肌的功能下降。头颈夹肌表面肌电特征有助于早期诊断慢性非特异性颈部不适飞行员的肌肉功能状态的改变。     

Flexion–relaxation ratio in computer workers with and without chronic neck pain

This study evaluated the flexion–relaxation phenomenon (FRP) and flexion–relaxation ratios (FR-ratios) using surface electromyography (sEMG) of the cervical extensor muscles of computer workers with and without chronic neck pain, as well as of healthy subjects who were not computer users. This study comprised 60 subjects 20–45 years of age, of which 20 were computer workers with chronic neck pain (CPG), 20 were computer workers without neck pain (NPG), and 20 were control individuals who do not use computers for work and use them less than 4 h/day for other purposes (CG). FRP and FR-ratios were analyzed using sEMG of the cervical extensors. Analysis of FR-ratios showed smaller values in the semispinalis capitis muscles of the two groups of workers compared to the control group. The reference FR-ratio (flexion relaxation ratio [FRR], defined as the maximum activity in 1 s of the re-extension/full flexion sEMG activity) was significantly higher in the computer workers with neck pain compared to the CG (CPG: 3.10, 95% confidence interval [CI95%] 2.50–3.70; NPG: 2.33, CI95% 1.93–2.74; CG: 1.99, CI95% 1.81–2.17; p < 0.001). The FR-ratios and FRR of sEMG in this study suggested that computer use could increase recruitment of the semispinalis capitis during neck extension (concentric and eccentric phases), which could explain our results. These results also suggest that the FR-ratios of the semispinalis may be a potential functional predictive neuromuscular marker of asymptomatic neck musculoskeletal disorders since even asymptomatic computer workers showed altered values. On the other hand, the FRR values of the semispinalis capitis demonstrated a good discriminative ability to detect neck pain, and such results suggested that each FR-ratio could have a different application.     

Assessment of neuromuscular activity during maximal isometric contraction in supine vs standing body positions

BackgroundWhen comparing neuromuscular activity between different individuals or different conditions by use of surface electromyography (sEMG) it is necessary to apply standardized assessment protocol. Most frequently used method is the maximum voluntary isometric contraction (MVIC). However, the influence of body posture on sEMG activity during MVIC testing remains largely unknown.AimTo evaluate the MVIC method for sEMG normalization in supine versus standing positions for selected muscles of the lower extremity and trunk.MethodsTwelve healthy individuals participated; five females and seven males (age 22–51 yrs). sEMG signals were recorded bilaterally from mm tibialis anterior, gluteus medius, adductor longus, rectus abdominus, external oblique and internal oblique/transversus abdominus according to standardized test protocol. Two different body positions were used: supine and standing position.ResultsMVIC peak sEMG signal amplitudes did not differ systematically between supine and standing test positions. Pronounced inter-subject variability in MVIC reference sEMG activity were observed between participants, during both supine and standing test positions.ConclusionPresent data demonstrate that MVIC EMG normalization is a biomechanically stable procedure that can be performed in a reproducible manner for the major leg and trunk muscles when comparing supine vs. standing test positions.     

Surface EMG pattern recognition for real-time control of a wrist exoskeleton

Background  

Surface electromyography (sEMG) signals have been used in numerous studies for the classification of hand gestures and movements and successfully implemented in the position control of different prosthetic hands for amputees. sEMG could also potentially be used for controlling wearable devices which could assist persons with reduced muscle mass, such as those suffering from sarcopenia. While using sEMG for position control, estimation of the intended torque of the user could also provide sufficient information for an effective force control of the hand prosthesis or assistive device. This paper presents the use of pattern recognition to estimate the torque applied by a human wrist and its real-time implementation to control a novel two degree of freedom wrist exoskeleton prototype (WEP), which was specifically developed for this work.     

A thin, flexible multielectrode grid for high-density surface EMG.

Although the value of high-density surface electromyography (sEMG) has already been proven in fundamental research and for specific diagnostic questions, there is as yet no broad clinical application. This is partly due to limitations of construction principles and application techniques of conventional electrode array systems. We developed a thin, highly flexible, two-dimensional multielectrode sEMG grid, which is manufactured by using flexprint techniques. The material used as electrode carrier (Polyimid, 50 microm thick) allows grids to be cut out in any required shape or size. One universal grid version can therefore be used for many applications, thereby reducing costs. The reusable electrode grid is attached to the skin by using specially prepared double-sided adhesive tape, which allows the selective application of conductive cream only directly below the detection surfaces. To explore the practical possibilities, this technique was applied in single motor unit analysis of the facial musculature. The high mechanical flexibility allowed the electrode grid to follow the skin surface even in areas with very uneven contours, resulting in good electrical connections in the whole recording area. The silverchloride surfaces of the electrodes and their low electrode-to-skin impedances guaranteed high baseline stability and a low signal noise level. The electrode-to-skin attachment proved to withstand saliva and great tensile forces due to mimic contractions. The inexpensive, universally adaptable and minimally obstructive sensor allows the principal advantages of high-density sEMG to be extended to all skeletal muscles accessible from the skin surface and may lay the foundation for more broad clinical application of this noninvasive, two-dimensional sEMG technique.     

Quantifying Forearm Muscle Activity during Wrist and Finger Movements by Means of Multi-Channel Electromyography

The study of hand and finger movement is an important topic with applications in prosthetics, rehabilitation, and ergonomics. Surface electromyography (sEMG) is the gold standard for the analysis of muscle activation. Previous studies investigated the optimal electrode number and positioning on the forearm to obtain information representative of muscle activation and robust to movements. However, the sEMG spatial distribution on the forearm during hand and finger movements and its changes due to different hand positions has never been quantified. The aim of this work is to quantify 1) the spatial localization of surface EMG activity of distinct forearm muscles during dynamic free movements of wrist and single fingers and 2) the effect of hand position on sEMG activity distribution. The subjects performed cyclic dynamic tasks involving the wrist and the fingers. The wrist tasks and the hand opening/closing task were performed with the hand in prone and neutral positions. A sensorized glove was used for kinematics recording. sEMG signals were acquired from the forearm muscles using a grid of 112 electrodes integrated into a stretchable textile sleeve. The areas of sEMG activity have been identified by a segmentation technique after a data dimensionality reduction step based on Non Negative Matrix Factorization applied to the EMG envelopes. The results show that 1) it is possible to identify distinct areas of sEMG activity on the forearm for different fingers; 2) hand position influences sEMG activity level and spatial distribution. This work gives new quantitative information about sEMG activity distribution on the forearm in healthy subjects and provides a basis for future works on the identification of optimal electrode configuration for sEMG based control of prostheses, exoskeletons, or orthoses. An example of use of this information for the optimization of the detection system for the estimation of joint kinematics from sEMG is reported.     

The influence of providing feedback on force production and within-participant reproducibility during maximal voluntary exertions for the anterior deltoid,middle deltoid,and infraspinatus

The normalization of electromyographic signals to a maximum voluntary reference contraction is common practice within the ergonomics research paradigm. However, there is a lack of support for a common protocol for obtaining maximum repeatable exertions. Specifically, there is minimal evidence to support the use of providing force magnitude feedback during the production of voluntary maximum exertions (MVE) in terms of both signal amplitude and repeatability. Therefore, the purpose of this study was to determine (1) if an MVE force magnitude feedback protocol increased both the force exerted and corresponding muscle activity, (2) if force magnitude feedback improved the within-participant reproducibility of the force or activity observed, and (3) if the surface electromyography (sEMG) signal processing method affected the repeatability of determining peak muscle activity.Seventeen participants completed a series of MVEs; first without feedback of the forces they produced, then with feedback of the forces they were producing, and again without feedback to determine if providing force feedback influenced their ability to produce a maximum force. Hand force and sEMG from the anterior deltoid, middle deltoid, and infraspinatus were measured during each exertion. The results showed that the highest forces and muscle activities were achieved when force feedback was provided. Force magnitude feedback resulted in a 7–22% increase in magnitude (for force and activity) and a decrease of 11–46% in the coefficient of variation specifying an improvement in the within-participant reproducibility. Signal processing techniques also affected within-participant reproducibility, however to a much lesser extent. The peak value from a 500-ms moving window average of the linear enveloped or root mean squared sEMG was the most reproducible technique tested.     

Whole-body vibration increases upper and lower body muscle activity in older adults: potential use of vibration accessories

The current study examined the effects of whole-body vibration (WBV) on upper and lower body muscle activity during static muscle contractions (squat and bicep curls). The use of WBV accessories such as hand straps attached to the platform and a soft surface mat were also evaluated. Surface electromyography (sEMG) was measured for the medial gastrocnemius (MG), vastus lateralis (VL), and biceps brachii (BB) muscles in fourteen healthy older adults (74.8±4.5 years; mean±SD) with a WBV stimulus at an acceleration of 40 m s(-2) (30 Hz High, 2.5 mm or 46 Hz Low, 1.1 mm). WBV increased lower body (VL and MG) sEMG vs baseline (no WBV) though this was decreased with the use of the soft mat. The addition of the bicep curl with hand straps had no effect on lower body sEMG. WBV also increased BB sEMG vs baseline which was further increased when using the hand straps. There was no upper body effect of the soft mat. This study demonstrates WBV increases both lower and upper body muscle activity in healthy older adults. Moreover, WBV accessories such as hand straps attached to the platform or a soft surface mat may be used to alter exercise intensity.     

Evidence of muscle synergies during human grasping

Motor synergies have been investigated since the 1980s as a simplifying representation of motor control by the nervous system. This way of representing finger positional data is in particular useful to represent the kinematics of the human hand. Whereas, so far, the focus has been on kinematic synergies, that is common patterns in the motion of the hand and fingers, we hereby also investigate their force aspects, evaluated through surface electromyography (sEMG). We especially show that force-related motor synergies exist, i.e. that muscle activation during grasping, as described by the sEMG signal, can be grouped synergistically; that these synergies are largely comparable to one another across human subjects notwithstanding the disturbances and inaccuracies typical of sEMG; and that they are physiologically feasible representations of muscular activity during grasping. Potential applications of this work include force control of mechanical hands, especially when many degrees of freedom must be simultaneously controlled.     

Comparison of surface electromyographic activity of erector spinae before and after the application of central posteroanterior mobilisation on the lumbar spine

Lumbar spine accessory movements, used by therapists in the treatment of patients with low back pain, is thought to decrease paravertebral muscular activity; however there is little research to support this suggestion. This study investigated the effects of lumbar spine accessory movements on surface electromyography (sEMG) activity of erector spinae.A condition randomised, placebo controlled, repeated measures design was used. sEMG measurements were recorded from 36 asymptomatic subjects following a control, placebo and central posteroanterior (PA) mobilisation to L3 each for 2 min. The therapist stood on a force platform while applying the PA mobilisation to quantify the force used. The PA mobilisation applied to each subject had a mean maximum force of 103.3 N, mean amplitude of force oscillation of 41.1 N, and a frequency of 1.2 Hz. Surface electromyographic data were recorded from the musculature adjacent to L3, L5 and T10.There were statistically significant reductions of 15.5% (95% CI: 8.0–22.5%) and 17.8% (95% CI: 12.9–22.4%) in mean sEMG values following mobilisation compared with the control and placebo, respectively.This study demonstrates that a central PA mobilisation to L3 results in a statistically significant decrease in the sEMG activity of erector spinae of an asymptomatic population.     

Electromyographic models to assess muscle fatigue

Muscle fatigue is a common experience in daily life. Many authors have defined it as the incapacity to maintain the required or expected force, and therefore, force, power and torque recordings have been used as direct measurements of muscle fatigue. In addition, the measurement of these variables combined with the measurement of surface electromyography (sEMG) recordings (which can be measured during all types of movements) during exercise may be useful to assess and understand muscle fatigue. Therefore, there is a need to develop muscle fatigue models that relate changes in sEMG variables with muscle fatigue. However, the main issue when using conventional sEMG variables to quantify fatigue is their poor association with direct measures of fatigue. Therefore, using different techniques, several authors have combined sets of sEMG parameters to assess muscle fatigue. The aim of this paper is to serve as a state-of-the-art summary of different sEMG models used to assess muscle fatigue. This paper provides an overview of linear and non-linear sEMG models for estimating muscle fatigue, their ability to assess power loss and their limitations due to neuromuscular changes after a training period.     

Acute effects of whole-body vibration on neuromuscular responses in older individuals: implications for prescription of vibratory stimulation

The aim of this study was to analyze surface electromyography activity (sEMG) and rating of perceived exertion (RPE) responses in different muscles while standing on a vibrating platform producing oscillations of different frequencies and amplitudes. Twenty community-dwelling older adults (79.6 ± 3.2 years) took part in the research. Subjects were exposed to 12 different vibration treatments of 15 seconds separated by 1 minute of rest in random order to check the influence of frequency (25, 35, and 45 Hz) and amplitude (1 mm [low] and 3.1 mm [high]) vibration on sEMG signal and RPE. Additionally, the use of a soft pad was also examined for its influence on these measures. Three-factor analysis of variance for RPE and both lower and whole-body sEMGs revealed a significant amplitude main effect (p < 0.01), and soft mat effect (p < 0.01), and a significant frequency main effect (p < 0.01). The major findings were that sEMG and RPE increased with the acceleration of the vibration; moreover, the increments of sEMG were highly correlated with RPE. The results of this study suggest that using the RPE method after each exercise would allow exercise and health professionals to assess the intensity levels that correspond to the level of the vibratory program in older adults.     

Surface electromyography in animal biomechanics: A systematic review

The study of muscle activity using surface electromyography (sEMG) is commonly used for investigations of the neuromuscular system in man. Although sEMG has faced methodological challenges, considerable technical advances have been made in the last few decades. Similarly, the field of animal biomechanics, including sEMG, has grown despite being confronted with often complex experimental conditions. In human sEMG research, standardised protocols have been developed, however these are lacking in animal sEMG. Before standards can be proposed in this population group, the existing research in animal sEMG should be collated and evaluated. Therefore the aim of this review is to systematically identify and summarise the literature in animal sEMG focussing on (1) species, breeds, activities and muscles investigated, and (2) electrode placement and normalisation methods used. The databases PubMed, Web of Science, Scopus, and Vetmed Resource were searched systematically for sEMG studies in animals and 38 articles were included in the final review. Data on methodological quality was collected and summarised. The findings from this systematic review indicate the divergence in animal sEMG methodology and as a result, future steps required to develop standardisation in animal sEMG are proposed.     

Network modeling and analysis of lumbar muscle surface EMG signals during flexion–extension in individuals with and without low back pain

In this paper, we propose modeling the activity coordination network between lumbar muscles using surface electromyography (sEMG) signals and performing the network analysis to compare the lumbar muscle coordination patterns between patients with low back pain (LBP) and healthy control subjects. Ten healthy subjects and eleven LBP patients were asked to perform flexion–extension task, and the sEMG signals were recorded. Both the subject-level and the group-level PC_fdr algorithms are applied to learn the sEMG coordination networks with the error-rate being controlled. The network features are further characterized in terms of network symmetry, global efficiency, clustering coefficient and graph modules. The results indicate that the networks representing the normal group are much closer to the order networks and clearly exhibit globally symmetric patterns between the left and right sEMG channels. While the coordination activities between sEMG channels for the patient group are more likely to cluster locally and the group network shows the loss of global symmetric patterns. As a complementary tool to the physical and anatomical analysis, the proposed network analysis approach allows the visualization of the muscle coordination activities and the extraction of more informative features from the sEMG data for low back pain studies.     

表面肌电信号采集与降噪处理

目的:本文以设计的表面肌电(sEMG)信号采集系统为基础,探讨sEMG信号中的降噪处理问题。方法:结合sEMG信号的噪声影响情况,首先利用带通滤波器消除肌电信号频带外噪声,再通过频谱插值法来抑制工频干扰分量,最后使用小波分析方法来削弱肌电信号频带内噪声。结果:通过对检测sEMG信号的降噪处理,信号噪声得到明显抑制。结论:所设计采集系统能够获得满意的sEMG信号检测效果,所采用降噪方法能够有效提高sEMG信号的质量。     

Exercise induced muscle damage and recovery assessed by means of linear and non-linear sEMG analysis and ultrasonography.

This study was aimed at investigating the time-course and recovery from eccentric (EC) exercise induced muscle damage by means of surface electromyography (sEMG), ultrasonography (US), and blood enzymes. Five subjects (EC Group) performed two bouts of 35 EC maximum contractions with the biceps brachii of their non dominant arm, five subjects were tested without performing EC (Control Group: CNT). The maximal isometric force (MVC) was measured. Force and sEMG signals were recorded during 80% MVC isometric contractions. In EC and CNT subjects US assessment on non-dominant biceps brachii was performed; creatin kinase (CK) and lactic dehydrogenasis (LDH) plasma levels were also assessed. Force, sEMG and CK-LDH measurements were performed before EC and after it periodically for 4 weeks. The sEMG was analysed in time and frequency domains; a non-linear analysis (Lyapunov 1st exponent, L1) of sEMG was also performed. After EC, the MVC was reduced by 40% on average with respect to the pre-EC values. A significant decrease in the initial frequency content, and in the MDF and L1 decay (13-42% less than the pre-EC values, respectively) was also observed. The sEMG amplitude (Root Mean Square, RMS) was unchanged after EC. The US revealed an increase in muscle belly thickness and in local muscle blood flow after EC. A complete recovery of all the considered parameters was achieved in two weeks. In conclusion sEMG analysis was confirmed as an early indicator of muscle damage. Muscle recovery from damage is followed by both sEMG and US and this may have useful clinical implications. Non linear analysis (L1) was revealed to be sensitive to early sEMG modifications induced by EC as well as able to follow the post EC changes in the sEMG.     

Relation between object properties and EMG during reaching to grasp

In order to stably grasp an object with an artificial hand, a priori knowledge of the object’s properties is a major advantage, especially to ensure subsequent manipulation of the object held by the hand. This is also true for hand prostheses: pre-shaping of the hand while approaching the object, similar to able-bodied, allows the wearer for a much faster and more intuitive way of handling and grasping an object. For hand prostheses, it would be advantageous to obtain this information about object properties from a surface electromyography (sEMG) signal, which is already present and used to control the active prosthetic hand.We describe experiments in which human subjects grasp different objects at different positions while their muscular activity is recorded through eight sEMG electrodes placed on the forearm. Results show that sEMG data, gathered before the hand is in contact with the object, can be used to obtain relevant information on object properties such as size and weight.     

表面肌电信号采集与降噪处理

目的：本文以设计的表面~g（sEMG）信号采集系统为基础,探讨sEMG信号中的降噪处理问题。方法：结合sEMG信号的噪声影响情况,首先利用带通滤波器消除肌电信号频带外噪声,再通过频谱插值法来抑制工频干扰分量,最后使用小波分析方法来削弱肌电信号频带内噪声。结果：通过对检测sEMG信号的降噪处理,信号噪声得到明显抑制。结论：所设计采集系统能够获得满意的sEMG信号检测效果,所采用降噪方法能够有效提高sEMG信号的质量。     

Assessment of repeatability of surface electromyography signals by singular value decomposition

Singular value decomposition (SVD) of full-wave rectified surface electromyography (sEMG) signals was investigated for repeatability indices of sEMG linear envelopes (LE) during biceps curl. The SVD based repeatability indices were compared with a well-known method, the variance ratio (VR). The usefulness of the offered indices was examined by a simulation and it was applied to the sEMG LEs. The results have shown that the VRs were correlated with the SVD based indices significantly. The usefulness of the offered indices on real world EMG signals practically comes from decreasing amplitudes of the first few singular values of EMG LE matrix. If repeatability is high, singular values decay fast and vice versa.If justified by further researches, the offered indices may be used practically for repeatability measurement of sEMG LEs.