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  • EMD

    Greetings All:

    In an earlier paper (Gabriel & Boucher, EJAP 1998, 79:37-40), we assumed
    that EMD was related to excitation and contraction-coupling and generating
    enough tension in the SEC so that force could be transmitted to the tendon
    and move the limb. If so, it should be affected by dynamic training which
    alters muscle activation . So, we divided the EMG burst into two
    components EMD and END. The END portion was from the onset of movement
    until the end of the burst. The portions did respond differently. The END
    portion of the burst decreased in duration as subjects increased the speed
    of limb movement. The duration EMD portion remained "relatively"
    stable. We did note that 100 maximal effort contractions decreased its
    duration "within" each training session, but were unable to find an across
    sessions training effect.

    How we filtered the data was an important issue. It affected the absolute
    magnitude of the observed results, not the appearance of them. That is,
    experimental affects were real, no matter how we filtered the data: i.e.,
    band-passed versus linear envelope detection as per Winter (3rd Ed).

    In my experience, EMG can be as long as 25-50 ms for isotonic contractions
    of the elbow flexors (Gabriel & Boucher, 1998), or as low as 10-15 ms for
    isometric contractions of the elbow flexors (Gabriel, Basford, & An, JEK
    2001, 11: 123-129). There are figures in both of these papers which show
    the differences in EMD for different contraction modalities. Both studies
    used a zero phase Butterworth, band-pass filter. The earlier paper also
    outline the algorithm for EMG burst onset and termination, which has been
    requested many times in this forum.

    One last point. I have noticed that EMD values for isotonic contractions
    are shorter when using acceleration to determine the onset of movement
    versus an event marker triggered by a microswitch; there are additional
    'slight' delays associated with the electronics. I also read this is
    another paper but can't remember the citation.

    Best Wishes,


    David A. Gabriel, Ph.D., FACSM
    Department of Physical Education and Kinesiology
    Brock University
    St. Catharines, Ontario, CANADA
    L2S 3A1

    Phone: 905-688-5550 ext.4362
    FAX: 905-688-8364

    "I learn from my mistakes. I can repeat them perfectly"