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Electromyographic Manifestations of Muscular Fatigue

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This increase is due to recruitment of motor units to compensate for the loss of ... MVC of elbow flexors and plantar flexors was measured ... – PowerPoint PPT presentation

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Title: Electromyographic Manifestations of Muscular Fatigue


1
Electromyographic Manifestations of Muscular
Fatigue
  • Toshio Moritani, Akira Nagata and Masuo Muro

2
Introduction
  • IEMG increases progressively as a function of
    time during sustained muscular contraction with a
    constant force output.
  • This increase is due to recruitment of motor
    units to compensate for the loss of contractility
    due to some degree of impairment of fatigued Mus.
  • EMG fatigue curves (EMG Amplitude vs Time) could
    provide a measure of MUs fatigability.

3
Methods
  • 8 male subjects
  • MVC of elbow flexors and plantar flexors was
    measured
  • The subjects were then instructed to maintain
    isometric contractions at 30, 40, 60 and 80 MVC
    for as long as possible.
  • A 45 minute rest was allowed between contractions
  • Subject also completed 10 trials of 2-3 sec MVCs
    to obtain mean power frequency at MVC
  • Ag-Ag CL, 2 mm contact diameter and 6 mm
    interelectrode distance was used.

4
Methods
  • Fast Fourier Transform with the Hamming window
  • Mean Power Frequency was calculated from EMG
    frequency spectrum.
  • Fatigability was estimated by the rate of
    increase in IEMG as a function of time (IEMG
    Slope) at a given force output level.

5
EMG as a Function of Time
  • Despite the equivalent level of muscular effort,
    the IEMG Slope for the bicep was nine times
    greater than the soleus.

6
EMG Slope as a Function of MVC
7
Effects of Fatigue on Frequency Spectrum
  • MPF for the bicep at 40 MVC declined by 43.7 Hz
    after fatigue.
  • MPF for the soleus at 40 MVC declined by 7.3 Hz
    after fatigue.
  • The extent of decline in the MPF was correlated
    (r .95) with the MPF obtained during MVC.
  • This correlation suggested that MUs with higher
    MPF would fatigue to a greater extent than those
    with relatively lower MPF

8
Discussion
  • A muscle group composed of a higher percent of FT
    fibers would manifest a greater fatigability than
    that of lower percent of FT fibers.
  • Fatigue causes an increase in EMG amplitude
    followed by a decrease in EMG amplitude as a
    function of time.
  • Fatigue causes the frequency spectrum of the EMG
    signal to shift to lower frequencies.
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