Time frequency analysis of the electromyogram during fatigue
Biomedical Engineering Committee
Master of Science
Reisman, Stanley S.
Kristol, David S.
Findley, Thomas W.
Spectral parameters obtained from the surface EMG signal have been used as indicators of fatigue during a sustained contraction. These same parameters have not been tested with the EMG signals obtained from fine wire electrodes. One such parameter is the median frequency which is known to decline with fatigue. A comparison was done between the median frequencies obtained from the surface EMG and those obtained from the fine wire EMG. The median frequencies from both types of electrodes decreased with time indicating that fine wire electrodes could be used to measure fatigue.
In addition, a new technique, time frequency analysis, was applied to the EMG signal. This technique generates a continuos representation of the changing spectrum of the signal through time. Three types of time frequency distributions were applied to the EMG signal As predicted, differences existed between the distributions. The amplitude differential from the first time slice of the distribution to the last was the smallest for the STFT distribution. The Wigner-Ville distribution was spread out across the most frequencies. Walls appeared in the Choi-Williams distribution, but otherwise it was the most compressed. All the distributions displayed the expected spectral compression; however, more work is necessary to clarify the results.
njit-etd1994-023 (68 pages ~ 6,152 KB pdf)
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Created July 28, 2004