Power spectral changes of the vastus medialis electromyogram for graded isometric torques (I)
Yoo, J.H.; Herring, J.M.; Yu, J.
Electromyography and Clinical Neurophysiology 19(1-2): 183-197
1979
ISSN/ISBN: 0301-150X PMID: 499053 Document Number: 153540
Power spectral changes of the vastus medialis electromyogram (EMG) for graded isometric torque tensions, without fatigue effect, are analyzed for 10 healthy volunteers. Extended spectral ranges up to 1024 Hz using Fourier transform technique and enhancement of the frequency parameters using weighting functions show great promise in elucidating the recruiting and firing phenomena of the motor units. While substantial amplitude increases in lower spectrum ranges below 100-200 Hz are observed, higher frequency components are also noted to increase steadily from the early stage, which leads to a hypothesis that the motor units, gradually and alternately, utilize both the firing rate and the recruitment to accomodate the applied load. The total power spectrum area increases almost linearly, to a certain extent, with the normalized relative torque as indicated in the literature.