Probability density of the surface electromyogram and its relation to amplitude detectors
Probability density of the surface electromyogram and its relation to amplitude detectors
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DOI：
10.1109/10.764949
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发表时间：
1999-06-01
影响因子：
4.6
通讯作者：
Hogan, N
中科院分区：
文献类型：
--
作者：
Clancy, EA;Hogan, N
当表面肌电图（EMG）产生的恒定的力量，恒定的角度，nonfatiguing收缩建模为一个随机过程，其密度通常被假定为高斯。该假设导致均方根（RMS）处理作为EMG幅度的最大似然估计（其中EMG幅度被定义为随机过程的标准偏差）。与此理论公式相反，实验工作发现使用平均绝对值（MAV）处理的信噪比[（SNR），定义为幅度估计的平均值除以其标准偏差]上级RMS。本文回顾了高斯模型的RMS处理，然后推导出期望的（劣）SNR性能的MAV处理与高斯模型，接下来，一个新的模型，表面肌电信号，使用拉普拉斯密度，提出。它示出的MAV处理器是最大似然估计的EMG振幅的拉普拉斯模型。基于拉普拉斯模型的SNR性能被预测为劣于高斯模型的SNR性能约32%。因此，EMG的概率分布中的微小变化可能导致SNR性能的大幅度降低。最后，从恒定的力，恒定的角度，nonfatiguing收缩的实验数据进行了检查。实验观察到的密度落在理论高斯密度和拉普拉斯密度之间。平均而言，高斯密度最适合实验数据，尽管结果因受试者而异。对于幅度估计，MAV处理的SNR略高于RMS处理。
When the surface electromyogram (EMG) generated from constant-force, constant-angle, nonfatiguing contractions is modeled as a random process, its density is typically assumed to be Gaussian. This assumption leads to root-mean-square (RMS) processing as the maximum likelihood estimator of the EMG amplitude (where EMG amplitude is defined as the standard deviation of the random process). Contrary to this theoretical formulation, experimental work has found the signal-to-noise-ratio [(SNR), defined as the mean of the amplitude estimate divided by its standard deviation] using mean-absolute-value (MAV) processing to be superior to RMS. This paper reviews RMS processing with the Gaussian model and then derives the expected (inferior) SNR performance of MAV processing with the Gaussian model, Next, a new model for the surface EMG signal, using a Laplacian density, is presented. It is shown that the MAV processor is the maximum likelihood estimator of the EMG amplitude for the Laplacian model. SNR performance based on a Laplacian model is predicted to be inferior to that of the Gaussian model by approximately 32%. Thus, minor variations in the probability distribution of the EMG may result in large decrements in SNR performance. Lastly, experimental data from constant-force, constant-angle, nonfatiguing contractions were examined. The experimentally observed densities fell in between the theoretic Gaussian and Laplacian densities, On average, the Gaussian density best fit the experimental data, although results varied with subject. For amplitude estimation, MAV processing had a slightly higher SNR than RMS processing.