Leao Richardson N, Burne John A
School of Biomedical Sciences, University of Sydney, Sydney, NSW, Australia.
J Neurosci Methods. 2004 Feb 15;133(1-2):115-25. doi: 10.1016/j.jneumeth.2003.10.003.
This is the first reported use of the continuous wavelet transform (CWT) of the surface EMG (sEMG) to extract the reflex response to muscle stretch. We used a modulus-based method to estimate instantaneous amplitude-envelopes from ridges of the CWT (referred in this work as sEMG intensity) to extract the dynamic reflex response from sEMG. We tested the method on tendon reflexes where excellent temporal resolution is required to identify the different latency components, and on the tonic stretch reflex (tonic SR) response to an ongoing perturbation that characteristically has a low signal to noise ratio.
Eight subjects without neurological impairment were subjected to a series of archilles tendon taps and a 2 min continuous perturbation of the ankle using a pseudo-sinusoidal stretch profile containing frequencies from 0.1 to 8.0 Hz. The tendon reflexes were assessed in the soleus muscle at 10% of MVC and the tonic SR in tibialis anterior while the muscle was relaxed, at 5 and 10% of maximal voluntary contraction. Root mean square (RMS) and wavelet ridge extraction was applied to the sEMG signal to extract sEMG amplitudes (RMS) and intensities for all reflexes. To obtain the tonic SR, these estimates and those from the sEMG-RMS were subsequently cross-correlated with the perturbation record to yield 2 sets of estimates of reflex gain and coherence for comparison.
The sEMG intensities were highly correlated with the torques resulting from a ramped voluntary contraction. Following tendon taps, the method resolved the M1, M2, M3 response components at accurate latencies and with more complete reconstruction of the components than RMS-derived estimates. The wavelet ridge estimates extracted the tonic SR from resting and contracting muscles with significantly higher coherence than RMS estimates. Reflex gain, when estimated from sEMG intensity or sEMG-RMS, demonstrated similar relationships to the perturbation frequency and background contraction level. When the sEMG intensity reflex gain estimates from different subjects were pooled, they showed significantly lower variance about the mean than gain estimates derived from the rectified sEMG.
Wavelet-ridge extraction provides a valid approach to reflex evaluation from sEMG that does not depend on the absolute amplitude of the potentials measured at the EMG electrodes. This may have substantial advantages in more directly comparing responses between subjects on an absolute frequency scale without the need for normalisation against maximal contraction levels.
这是首次报道使用表面肌电图（sEMG）的连续小波变换（CWT）来提取肌肉拉伸的反射反应。我们使用基于模量的方法从CWT的脊线估计瞬时幅度包络（在本研究中称为sEMG强度），以从sEMG中提取动态反射反应。我们在需要出色的时间分辨率以识别不同潜伏期成分的腱反射以及对持续扰动的紧张性牵张反射（紧张性SR）反应（其特征是信噪比低）上测试了该方法。
八名无神经功能障碍的受试者接受了一系列跟腱轻敲，并使用包含0.1至8.0Hz频率的伪正弦拉伸曲线对踝关节进行了2分钟的连续扰动。在比目鱼肌以最大自主收缩（MVC）的10%评估腱反射，在胫骨前肌以最大自主收缩的5%和10%且肌肉放松时评估紧张性SR。将均方根（RMS）和小波脊线提取应用于sEMG信号，以提取所有反射的sEMG幅度（RMS）和强度。为了获得紧张性SR，随后将这些估计值以及来自sEMG-RMS的估计值与扰动记录进行互相关，以产生两组反射增益和相干性估计值进行比较。
sEMG强度与递增性自主收缩产生的扭矩高度相关。在进行跟腱轻敲后，该方法在准确的潜伏期解析了M1、M2、M3反应成分，并且与基于RMS的估计相比，成分的重建更完整。小波脊线估计从静息和收缩的肌肉中提取紧张性SR，其相干性明显高于RMS估计。当从sEMG强度或sEMG-RMS估计反射增益时，其与扰动频率和背景收缩水平呈现相似的关系。当汇总来自不同受试者的sEMG强度反射增益估计值时，它们围绕平均值的方差明显低于从整流后的sEMG得出的增益估计值。
小波脊线提取为从sEMG进行反射评估提供了一种有效的方法，该方法不依赖于在肌电图电极处测量的电位的绝对幅度。这在以绝对频率尺度更直接地比较受试者之间的反应而无需针对最大收缩水平进行归一化方面可能具有实质性优势。
