St-Amant Y, Rancourt D, Clancy E A
Mechanical Engineering Department, Laval University, Québec, Canada.
IEEE Trans Biomed Eng. 1998 Jun;45(6):795-800. doi: 10.1109/10.678614.
A systematic, experimental study of the influence of smoothing window length on the signal-to-noise ratio (SNR) of electromyogram (EMG) amplitude estimates is described. Surface EMG waveforms were sampled during nonfatiguing, constant-force, constant-angle contractions of the biceps or triceps muscles, over the range of 10%-75% maximum voluntary contraction. EMG amplitude estimates were computed with eight different EMG processor schemes using smoothing length durations spanning 2.45-500 ms. An SNR was computed from each amplitude estimate (deviations about the mean value of the estimate were considered as noise). Over these window lengths, average +/- standard deviation SNR's ranged from 1.4 +/- 0.28 to 16.2 +/- 5.4 for unwhitened single-channel EMG processing and from 3.2 +/- 0.7 to 37.3 +/- 14.2 for whitened, multiple-channel EMG processing (results pooled across contraction level). It was found that SNR increased with window length in a square root fashion. The shape of this relationship was consistent with classic theoretical predictions, however none of the processors achieved the absolute performance level predicted by the theory. These results are useful in selecting the length of the smoothing window in traditional surface EMG studies. In addition, this study should contribute to the development of EMG processors which dynamically tune the smoothing window length when the EMG amplitude is time varying.
本文描述了一项关于平滑窗口长度对肌电图（EMG）幅度估计信噪比（SNR）影响的系统实验研究。在肱二头肌或肱三头肌进行非疲劳、恒力、恒角度收缩过程中，采集表面肌电图波形，收缩强度范围为最大自主收缩的10%-75%。使用八种不同的肌电图处理器方案，通过2.45-500毫秒的平滑时长来计算肌电图幅度估计值。根据每个幅度估计值计算信噪比（估计值围绕平均值的偏差被视为噪声）。在这些窗口长度范围内，未白化单通道肌电图处理的平均±标准差信噪比范围为1.4±0.28至16.2±5.4，白化多通道肌电图处理的范围为3.2±0.7至37.3±14.2（结果汇总了不同收缩水平的数据）。研究发现，信噪比随窗口长度呈平方根方式增加。这种关系的形状与经典理论预测一致，然而没有一个处理器达到理论预测的绝对性能水平。这些结果对于在传统表面肌电图研究中选择平滑窗口长度很有用。此外，本研究应有助于开发在肌电图幅度随时间变化时能动态调整平滑窗口长度的肌电图处理器。
