局部肌肉疲劳的表面肌电信号复杂度和熵变化

目的 在于探讨静态和动态疲劳性运动过程中肱二头肌和腰部脊竖肌表面肌电(surface electromyography,sEMG)信号的Lempel-Ziv复杂度和Kolmogorov熵的变化规律。18名男性大学生志愿者被随机分为肱二头肌和腰部脊竖肌运动负荷组,分别完成静态和动态疲劳运动负荷试验。运动负荷期间连续记录sEMG信号,在对运动负荷时间和重复次数进行标准化处理后,截取相应时段的sEMG信号,计算Lempel-Ziv复杂度和Kolmogorov熵,观察它们随肌肉疲劳发展的变化规律。研究结果表明,无论是静态还是动态疲劳运动条件下,被检肌肉sEMG信号的复杂度和熵均随着运动负荷时间呈现明显的单调递减型变化。该变化可能与神经系统渐进性协调众多运动单位同步收缩的‘协同效应”有关。     

不同上肢预负荷对腰部肌肉自愿收缩力量的影响

目的：本研究探索不同上肢预负荷方式和强度对腰部肌肉最大自愿收缩力量的影响。方法：本研究共招募20名被试者,每名被试者以随机的顺序先后参加4组实验。在实验过程中,被试者保持中立正直坐姿,分别在无预负荷、举臂预负荷、手拉预负荷和手握预负荷方式下进行腰部和腹部力量全力共激活,每组预负荷方式的预负荷强度设置为20%和40%最大负荷力量,同时记录双侧腰部多裂肌和竖脊肌的肌电信号。结果：在双侧多裂肌中,举臂和手拉预负荷方式的均方根值（RMS）和积分肌电值（IEMG）均大于无预负荷组（P<0.05）,手握预负荷方式和无预负荷组之间的RMS值和IEMG值无统计学差异（P>0.05）;在双侧竖脊肌中,三种预负荷方式和无预负荷组之间的RMS值和IEMG值均无统计学差异（P>0.05）。在不同预负荷方式比较中,举臂和手拉预负荷方式的RMS值和IEMG值均大于手握预负荷方式（P<0.05）,举臂预负荷的RMS值和IEMG值均大于手拉预负荷方式（P<0.05）。结论：举臂和手拉预负荷方式带来的肌肉预激活均可以有效提高腰部多裂肌的自愿收缩力量,预负荷强度越大,肌肉收缩力量可能也越大,...     

肌肉动态收缩期间表面肌电信号的时频分析

介绍了用于肌肉动态收缩期间非平稳表面肌电信号的时频分析方法。用短时傅里叶变换、Wigner-Ville分布及Choi-Williams分布计算了表面肌电信号的时频分布,用于信号频率内容随时间演化的可视化观察。通过计算瞬时频谱参数,对肌肉疲劳的电表现进行量化描述。分析了反复性的膝关节弯曲和伸展运动期间从股外侧肌所记录的表面肌电信号。发现和在静态收缩过程中观察到的平均频率线性下降不同,在动态收缩期间瞬时平均频率的变化过程是非线性的并且更为复杂,且与运动的生物力学条件有关。研究表明将时频分析技术应用于动态收缩期间的表面肌电信号可以增加用传统的频谱分析技术不能得到的信息。     

肌电信号的特征分析方法及其应用

肌电信号是产生肌力的生物电信号来源,反映了神经-肌肉系统在进行随意性和非随意性活动时的生物电变化情况,它与神经肌肉活动密切相关.伴随着肌电信号特征分析方法的日臻完善,蕴含在信号内的神经、肌肉信息,越来越多地被人们所掌握,并被广泛地应用于临床医学、康复医学、体育科学、医学工程学以及基础研究等诸多领域.因而肌电信号具有重要的应用价值和学术价值.现本文主要针对肌电信号的特征分析方法(时域分析、频谱分析、时频分析等方法)以及肌电信号相关领域的应用情况作以综述.     

基于表面肌电信号的人体动作识别算法研究进展

表面肌电信号(Surface Electromyography,sEMG)是通过相应肌群表面的传感器记录下来的一维时间序列非平稳生物电信号,不但反映了神经肌肉系统活动,对于反映相应动作肢体活动信息同样重要。而模式识别是肌电应用领域的基础和关键。为了在应用基于表面肌电信号模式识别中选取合适算法,本文拟对基于表面肌电信号的人体动作识别算法进行回顾分析,主要包括模糊模式识别算法、线性判别分析算法、人工神经网络算法和支持向量机算法。模糊模式识别能自适应提取模糊规则,对初始化规则不敏感,适合处理s EMG这样具有严格不重复的生物电信号;线性判别分析对数据进行降维,计算简单,但不适合大数据;人工神经网络可以同时描述训练样本输入输出的线性关系和非线性映射关系,可以解决复杂的分类问题,学习能力强;支持向量机处理小样本、非线性的高维数据优势明显,计算速度快。比较各方法的优缺点,为今后处理此类问题模式识别算法选取提供了参考和依据。     

基于支持向量机的表面肌电信号和加速度融合跌倒识别方法

目的:针对老人易跌倒和跌倒过后可能产生严重后果这一现实问题,通过将表面肌电信号和加速度融合,进一步优化采用支持向量机分类器下的包含跌倒在内的几种不同动作的分类效果。方法:提出基于表面肌电和加速度信号融合的跌倒识别算法,首先采集股直肌,股内侧肌,胫骨前肌和腓肠肌的表面肌电信号以及位于腰部的三轴加速度信号作为实验数据,然后利用滑动窗口法提取表面肌电和加速度信号的均方根值,最后针对人体日常活动和跌倒的运动特征,构建了支持向量机的分类器。结果:实验数据共计320组数据,包括3种日常活动和向前跌倒,其中160组数据作为训练集,另外160组数据作为测试集。对4种动作进行识别实验,算法的准确度为93.23%、灵敏度为92.4%、特异度为100%,达到了良好的分类效果。结论:基于支持向量机的表面肌电信号和加速度融合的跌倒识别算法分类效果良好,对于老人跌倒防护具有现实意义。     

复杂度脑电地形图研究

脑电地形图是近年脑电分析的热点之一。通过对各种复杂度算法的分析得出,近似熵由于所需要的时间序列长度较短,大大减少了脑电非平稳性所带来的困难,且无需粗粒化,在对生物医学信号的复杂度分析中有其一定的优点,采用近似熵对多道脑电信号的复杂度运算结果,通过空间插值,构建复杂性动态脑地形图,以便于观察大脑各部ＥＥＧ信号复杂度在同一时刻的相对强弱关系和这种关系随时间的变化。并通过对一些脑疾病患者脑电数据的分析,     

脑电图复杂度分析中的粗粒化问题II.量化对复杂度计算的影响

在对生物医学信号时间序列进行复杂度分析时,粗粒化预处理有可能会造成丢失原始信号中所蕴含的信息,甚至在某些情况下根本改变原信号的动力学性质.用计算机计算时的量化过程也是一种粗粒化,因此也有这类问题.通过对近似熵和我们所定义的C0复杂度这两种复杂度在不同量化精度下对一些典型时间序列复杂度分析的比较研究,发现一般说来量化精度对复杂度分析的影响不是很大,仅当对原始信号进行二值化等极端情况下,才会显著改变原信号的复杂性.对脑电信号进行计算表明上述结论是实际可取的.     

不同姿势久坐下女性腰部肌肉的sEMG信号变化

目的:观察女性受试者在不同坐姿久坐前后腰部肌肉表面肌电(sEMG)信号的变化,探讨不同姿势的久坐对竖脊肌功能状态的影响。方法:32名女性受试者随机分成4组,分别在4种不同的座椅(座椅A、B、C、D)上久坐2 h。记录受试者腰部竖脊肌在久坐前后2次最大随意收缩力量(MVC)测试中的sEMG信号,观察测试过程中的前3 s时频指标及全程频域指标的变化。结果:3 s的时频指标平均肌电振幅(AEMG)、平均功率谱频率(MPF)在不同坐姿久坐前后无显著性差异,其中AEMG在座椅B组中明显大于座椅A组;全程信号的频域指标MPF在久坐后显著减小,但在不同坐姿之间无显著性差异。结论:女性受试者在4种不同坐姿2 h久坐前后腰部竖脊肌的最大活动水平无明显改变;最大持续收缩能力在久坐后下降,但在不同坐姿间并无显著差异。     

基于高阶复杂性测度的心率变异信号分析

心率变异性反映了交感神经和迷走神经对心血管系统的综合调节作用,是评价心血管系统功能的重要指标。复杂度是描述时间信号序列信息量的一个重要参数,传统算法中的过分粗略化会丢失大量的有用信息,而高阶复杂度的引入可较大程度地避免这一问题。在利用Lorenz模型数据仿真的基础上,分别对25例正常人样本和25例充血性心力衰竭病人样本的心率变异信号的1～15阶Kolmogorov复杂度进行了计算,通过对比分析后确定,5阶Kolmogorov复杂度在临床医学上可以为分析心率变异信号获得更为理想的效果。     

Assessment of low back muscle fatigue by surface EMG signal analysis: methodological aspects.

This paper focuses on methodological issues related to surface electromyographic (EMG) signal detection from the low back muscles. In particular, we analysed (1) the characteristics (in terms of propagating components) of the signals detected from these muscles; (2) the effect of electrode location on the variables extracted from surface EMG; (3) the effect of the inter-electrode distance (IED) on the same variables; (4) the possibility of assessing fatigue during high and very low force level contractions. To address these issues, we detected single differential surface EMG signals by arrays of eight electrodes from six locations on the two sides of the spine, at the levels of the first (L1), the second (L2), and the fifth (L5) lumbar vertebra. In total, 42 surface EMG channels were acquired at the same time during both high and low force, short and long duration contractions. The main results were: (1) signal quality is poor with predominance of non-travelling components; (2) as a consequence of point (1), in the majority of the cases it is not possible to reliably estimate muscle fiber conduction velocity; (3) despite the poor signal quality, it was possible to distinguish the fatigue properties of the investigated muscles and the fatigability at different contraction levels; (4) IED affects the sensitivity of surface EMG variables to electrode location and large IEDs are suggested when spectral and amplitude analysis is performed; (5) the sensitivity of surface EMG variables to changes in electrode location is on average larger than for other muscles with less complex architecture; (6) IED influences amplitude initial values and slopes, and spectral variable initial values; (7) normalized slopes for both amplitude and spectral variables are not affected by IED and, thus, are suggested for fatigue analysis at different postures or during movement, when IED may change in different conditions (in case of separated electrodes); (8) the surface EMG technique at the global level of amplitude and spectral analysis cannot be used to characterize fatigue properties of low back muscles during very low level, long duration contractions since in these cases the non-stable MU pool has a major influence on the EMG variables. These considerations clarify issues only partially investigated in past studies. The limitations indicated above are important and should be carefully discussed when presenting surface EMG results as a means for low back muscle assessment in clinical practice.     

Inter-electrode spacing of surface EMG sensors: reduction of crosstalk contamination during voluntary contractions

We investigated the influence of inter-electrode spacing on the degree of crosstalk contamination in surface electromyographic (sEMG) signals in the tibialis anterior (target muscle), generated by the triceps surae (crosstalk muscle), using bar and disk electrode arrays. The degree of crosstalk contamination was assessed for voluntary constant-force isometric contractions and for dynamic contractions during walking. Single-differential signals were acquired with inter-electrode spacing ranging from 5 mm to 40 mm. Additionally, double differential signals were acquired at 10 mm spacing using the bar electrode array. Crosstalk contamination at the target muscle was expressed as the ratio of the detected crosstalk signal to that of the target muscle signal. The crosstalk contamination ratio approached a mean of 50% for the 40 mm spacing for triceps surae muscle contractions at 80% MVC and tibialis anterior muscle contractions at 10% MVC. For single differential recordings, the minimum crosstalk contamination was obtained from the 10 mm spacing. The results showed no significant differences between the bar and disk electrode arrays. During walking, the crosstalk contamination on the tibialis anterior muscle reached levels of 23% for a commonly used 22 mm spacing single-differential disk sensor, 17% for a 10 mm spacing single-differential bar sensor, and 8% for a 10 mm double-differential bar sensor. For both studies the effect of electrode spacing on crosstalk contamination was statistically significant. Crosstalk contamination and inter-electrode spacing should therefore be a serious concern in gait studies when the sEMG signal is collected with single differential sensors. The contamination can distort the target muscle signal and mislead the interpretation of its activation timing and force magnitude.     

Testing of instantaneity hypothesis for blind source separation of extensor indicis and extensor digiti minimi surface electromyograms

Human muscle activity can be assessed with surface electromyography (SEMG). Depending on electrode location and size, the recording volume under the sensor is likely to measure electrical potentials emanating from muscles other than the muscle of interest. This crosstalk issue makes interpretation of SEMG data difficult. The purpose of this paper was to study a crosstalk reduction technique called blind source separation (BSS). Most straightforward separation techniques rely on linearity and instantaneity (LI) of signal mixtures on the sensors. Literature on BSS for SEMG often makes hypothesis of linearity and instantaneity of the mixing model. Using simulation of SEMG mixtures and real SEMG recordings on the human extensor indicis (EI) and extensor digiti minimi (EDM) muscles during a task consisting of selective successive activations of EI and EDM muscles, cross-correlation between the sensors was proven to be directly dependent on instantaneity of the sources. Instantaneity hypothesis testing on real SEMG recordings showed that source instantaneity hypothesis is very sensitive to electrode location along the fibers direction. Source separation gains using JADE BSS algorithm depend strongly on instantaneity hypothesis. Using LI BSS on SEMG requires great attention to electrode positioning; we provide a tool to test these on EI/EDM muscles.     

Determination of daunomycin at a novel COOH/indium tin oxide ion implantation-modified electrode

A novel COOH+ ion implantation-modified indium tin oxide (COOH/ITO) electrode was prepared for the first time and applied for determination of daunomycin (or daunorubicin [DNR]). The electrode showed higher catalytic activity than bare ITO electrode with good reproducibility and stability. The determination condition of linear voltammetry was optimized. A calibration curve was obtained over the range 2.0 x 10(-7) to 5.0 x 10(-6)mol/L, with a correlation coefficient of 0.9909 and a limit of detection of 1.0 x 10(-7)mol/L. The selectivity of the electrode was illustrated by determination of DNR in samples prepared of urine. X-ray photoelectron spectroscopy (XPS) analysis results showed that the implanted COOH+ maintained characteristics of organic group -COOH. A field emission-scanning electron microscope (FSEM) result showed that the implanted surface caused defects and partial dislocations and formed many active centers.     

Comparison of erector spinae and hamstring muscle activities and lumbar motion during standing knee flexion in subjects with and without lumbar extension rotation syndrome

The aim of this study was to compare the activity of the erector spinae (ES) and hamstring muscles and the amount and onset of lumbar motion during standing knee flexion between individuals with and without lumbar extension rotation syndrome. Sixteen subjects with lumbar extension rotation syndrome (10 males, 6 females) and 14 healthy subjects (8 males, 6 females) participated in this study. During the standing knee flexion, surface electromyography (EMG) was used to measure muscle activity, and surface EMG electrodes were attached to both the ES and hamstring (medial and lateral) muscles. A three-dimensional motion analysis system was used to measure kinematic data of the lumbar spine. An independent-t test was conducted for the statistical analysis. The group suffering from lumbar extension rotation syndrome exhibited asymmetric muscle activation of the ES and decreased hamstring activity. Additionally, the group with lumbar extension rotation syndrome showed greater and earlier lumbar extension and rotation during standing knee flexion compared to the control group. These data suggest that asymmetric ES muscle activation and a greater amount of and earlier lumbar motion in the sagittal and transverse plane during standing knee flexion may be an important factor contributing to low back pain.     

A Finite Element Model Approach to Determine the Influence of Electrode Design and Muscle Architecture on Myoelectric Signal Properties

Introduction

Surface electromyography (sEMG) is the measurement of the electrical activity of the skeletal muscle tissue detected at the skin’s surface. Typically, a bipolar electrode configuration is used. Most muscles have pennate and/or curved fibres, meaning it is not always feasible to align the bipolar electrodes along the fibres direction. Hence, there is a need to explore how different electrode designs can affect sEMG measurements.

Method

A three layer finite element (skin, fat, muscle) muscle model was used to explore different electrode designs. The implemented model used as source signal an experimentally recorded intramuscular EMG taken from the biceps brachii muscle of one healthy male. A wavelet based intensity analysis of the simulated sEMG signal was performed to analyze the power of the signal in the time and frequency domain.

Results

The model showed muscle tissue causing a bandwidth reduction (to 20-92- Hz). The inter-electrode distance (IED) and the electrode orientation relative to the fibres affected the total power but not the frequency filtering response. The effect of significant misalignment between the electrodes and the fibres (60°- 90°) could be reduced by increasing the IED (25–30 mm), which attenuates signal cancellation. When modelling pennated fibres, the muscle tissue started to act as a low pass filter. The effect of different IED seems to be enhanced in the pennated model, while the filtering response is changed considerably only when the electrodes are close to the signal termination within the model. For pennation angle greater than 20°, more than 50% of the source signal was attenuated, which can be compensated by increasing the IED to 25 mm.

Conclusion

Differences in tissue filtering properties, shown in our model, indicates that different electrode designs should be considered for muscle with different geometric properties (i.e. pennated muscles).     

Spinal stiffness changes throughout the respiratory cycle.

Posteroanterior stiffness of the lumbar spine is influenced by factors, including trunk muscle activity and intra-abdominal pressure (IAP). Because these factors vary with breathing, this study investigated whether stiffness is modulated in a cyclical manner with respiration. A further aim was to investigate the relationship between stiffness and IAP or abdominal and paraspinal muscle activity. Stiffness was measured from force-displacement responses of a posteroanterior force applied over the spinous process of L2 and L4. Recordings were made of IAP and electromyographic activity from L4/L2 erector spinae, abdominal muscles, and chest wall. Stiffness was measured with the lung volume held at the extremes of tidal volume and at greater and lesser volumes. Stiffness at L4 and L2 increased above base-level values at functional residual capacity (L2 14.9 N/mm and L4 15.3 N/mm) with both inspiratory and expiratory efforts. The increase was related to the respiratory effort and was greatest during maximum expiration (L2 24.9 N/mm and L4 23.9 N/mm). The results indicate that changes in trunk muscle activity and IAP with respiratory efforts modulate spinal stiffness. In addition, the diaphragm may augment spinal stiffness via attachment of its crural fibers to the lumbar vertebrae.     

Effects of a passive exoskeleton on the mechanical loading of the low back in static holding tasks

With mechanical loading as the main risk factor for LBP in mind, exoskeletons are designed to reduce the load on the back by taking over a part of the required moment. The present study assessed the effect of a passive exoskeleton on back and abdominal muscle activation, hip and lumbar flexion and on the contribution of both the human and the exoskeleton to the L5/S1 net moment, during static bending at five different hand heights. Two configurations of the exoskeleton (LOW & HIGH) differing in angle-torque characteristics were tested. L5/S1 moments generated by the subjects were significantly reduced (15–20% for the most effective type) at all hand heights. LOW generated 4–11 Nm more support than HIGH at 50%, 25% and 0% upright stance hand height and HIGH generated 4–5 Nm more support than LOW at 100% and 75%. Significant reductions (11–57%) in back muscle activity were found compared to WITHOUT for both exoskeletons for some conditions. However, EMG reductions compared to WITHOUT were highly variable across subjects and not always significant. The device allowed for substantial lumbar bending (up to 70°) so that a number of participants showed the flexion-relaxation phenomenon, which prevented further reduction of back EMG by the device and even an increase from 2% to 6% MVC in abdominal activity at 25% hand height. These results indicate that flexion relaxation and its interindividual variation should be considered in future exoskeleton developments.     

Reinnervation of murine muscle following fetal sciatic nerve transection

A technique is reproted that permits transection of the sciatic nerve of mouse fetuses without interfering with fetal viability. Sciaticotomy was performed on Swiss Webster mice at day 17 of gestation; the contralateral side served as a control. Six weeks later the extensor digitorum longus (EDL) muscles on both sides were injected with horseradish peroxidase (HRP). Examination of the lumbar spinal cord revealed that while a substantial number of motor neurons in the region of the spinal cord giving rise to the sciatic nerve died, the EDL muscle did become reinnervated. The size of the EDL motor neuron pool on the denervated-reinnervated side was ～43% of that seen on the control side. While the control EDL motor neuron pool was located in lumbar segments L3–L5, the location of the pool to the denervated-reinnervated EDL was shifted cranially to L2–L4. Denervated-reinnervated EDL muscles were analyzed immunohistochemically to study the effect of fetal denervation on the neuronal cell adhesion molecule (N-CAM) expression. At 2 weeks postnatal, N-CAM immunoreactivity in control muscle was segregated to the motor end plate region, while fetally denervated muscle continued to express N-CAM along the length of the sarcolemma. Thus fetally denervated muscle does not develop the same pattern of N-CAM expression as normal, innervated muscle. By 6 weeks of age, the denervated-reinnervated muscle showed the same level and distribution of N-CAM immunoreactivity as did age-matched control muscle, indicating that most, if not all, of its myofibers had been reinnervated.