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Short time Fourier analysis of the electromyogram - Fast movements and constant contractionShort-time Fourier analysis was applied to surface electromyograms (EMG) recorded during rapid movements, and during isometric contractions at constant forces. A portion of the data to be transformed by multiplying the signal by a Hamming window was selected, and then the discrete Fourier transform was computed. Shifting the window along the data record, a new spectrum was computed each 10 ms. The transformed data were displayed in spectograms or 'voiceprints'. This short-time technique made it possible to see time-dependencies in the EMG that are normally averaged in the Fourier analysis of these signals. Spectra of EMGs during isometric contractions at constant force vary in the short (10-20 ms) term. Short-time spectra from EMGs recorded during rapid movements were much less variable. The windowing technique picked out the typical 'three-burst pattern' in EMG's from both wrist and head movements. Spectra during the bursts were more consistent than those during isometric contractions. Furthermore, there was a consistent shift in spectral statistics in the course of the three bursts. Both the center frequency and the variance of the spectral energy distribution grew from the first burst to the second burst in the same muscle. The analogy between EMGs and speech signals is extended to argue for future applicability of short-time spectral analysis of EMG.
Document ID
19870040971
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Hannaford, Blake
(California Institute of Technology Jet Propulsion Laboratory, Pasadena, United States)
Lehman, Steven
(California, University Berkeley, United States)
Date Acquired
August 13, 2013
Publication Date
December 1, 1986
Publication Information
Publication: IEEE Transactions on Biomedical Engineering
Volume: BME-33
ISSN: 0018-9294
Subject Category
Aerospace Medicine
Accession Number
87A28245
Distribution Limits
Public
Copyright
Other

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