| This paper introduces the physiological mechanism, research meaning and detection methods of surface electromyogram(SEMG). The significance and various research methods of muscle fatigue assessment are discussed in detail. Electrically evoked SEMG signals which are high repeatability and little influenced by noise were adopted in the experiment. Constant current electrical stimulator was used to stimulate sural nerve and the electrically evoked SEMG was amplified and detected by special biopotential measurement system. Influence of noise was lowered effectively on this condition.We study the characteristics of SEMG signal during muscle fatigue by wavelet analysis. On the basis of matched filter theory, Mexihat wavelet function which is matched to M-wave was chose to do wavelet tranaform. The time stretching of two semi-wave of M-wave were analyzed respectively based on the relation of maximum wavelet coefficients modulus and wavelet scale. Indexes of muscle fatigue were defined according as the scale of wavelet transform. And it realize the quantitative analysis during muscle fatigue. The analysis result of median frequency (MDF) and Lipschitz are also showed in the paper. Wavelet method overcome the limitation of Fourier Transform that it has no resolution in time domain and the results of experiment showed relative good repeatability. We look for indicators of SEMG which are correct, reliable and easy to interpret with this understanding and try to provide theoretic reference for the applications of these indicators. |
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