TIME-FREQUENCY ANALYSIS OF SURFACE MYOELECTRIC SIGNALS DURING DYNAMIC CONTRACTIONS
肌肉动态收缩期间表面肌电信号的时频分析

The time-frequency method analyzed the nonstationary surface myoelectric signals during muscle dynamic contractions was introduced. The time-frequency distribution of the surface myoelectric signal was computed by means of STFT?Wigner-Ville distribution and Choi-Williams distribution. They are used for the visual inspection of the evolution of the frequency content of the signal. The myoelectric signals collected from vastus lateralis during repetitive knee flexion-extension exercise was analyzed. Unlike the linear decrease in mean frequency observed in static contractions, instantaneous median frequency behavior was non-linear and more complex during dynamic contractions, which related to biomechanical conditions of the exercise. The electrical manifestations of muscle fatigue were quantified by computing spectral parameters of each spectral estimate. The results showed that the application of time-frequency analysis to surface myoelectric signal during dynamic contraction may obtain more information that was not available using the traditional spectral analysis techniques.