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Emg onset and cessation sum

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  • Emg onset and cessation sum

    Thank you for all your responses to my posting on EMG onset and cessation. I
    was enlightened by the responses and some more of my own digging. It surely
    seems to be a topic of interest as the reponses intimate. Sorry I took so
    long to sum these up, but here they are and Happy Holidays to all:

    You have identified a major limitation in the emg literature. Authors
    should provide their operational definitions for muscle onset and offset, or
    should indicate that the determination was made qualitatively and should
    indicate their reliability in making this qualitative determination.
    One quantitative method that has been used in our labs at UNC is to first
    collect resting emg levels and to report the conditions under which the
    resting emg data were acquired. The resting emg can then be demeaned and
    full-wave rectified. Any other signal processing that will be done to emg
    data acquired during the experiment (eg, low pass filter) is also performed on
    the data. The mean amplitude of the resting signal is then computed for a
    specific time period, usually one second. Muscle onset is then defined as any
    muscle activity whose amplitude excedes the mean plus three standard
    deviations of the resting signal. Additional criteria can be specified, such
    as: to qualify as an onset burst, the muscle must excede the minimum
    threshold for a minimum number of msec, and the muscle burst duration does
    not have an offset unless the amplitude falls below the threshold value for at
    least a specified period of time.
    I hope this helps.

    Michael Gross
    Division of Physical Therapy
    University of North Carolina at Chapel Hill
    phone: 919-966-4709

    Dear Steve,

    That's something I've been trying to find out also. I'd be interested
    to see what other people have to say, but here's one criterion I
    came across recently.

    At the CSB conference in August, there was a seminar on EMG given by
    Drs. Baratta and Solomonow. In their handout, they mention that
    Harris et al. (ref below) took the on-off threshold as 5% of the
    mean maximum voluntary muscle test value (after rectifying and
    low-pass filtering the signal to give the mean absolute value).

    The Harris reference is:
    Harris, GF, and Wertsch, JJ. "Procedures for gait analysis."
    Arch Phys Med Rehab, 75:216-225, 1994.

    Hope this helps.

    $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$$
    Danielle Toutoungi, D.Phil. Research Student,
    Oxford Orthopaedic Engineering Centre, University of Oxford.
    tel: ++ (0)1865 227684
    fax: ++ (0)1865 742348 email:

    "Time flies like an arrow, Fruit flies like a banana" - Anon.
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    I do not know how to answer your question, but I would be very interested
    in the responses that you get. I am a biomech grad student at the
    University of Delaware, and will be doing an internship of sorts at a gait
    analysis lab.

    If you have the time, could you either post a summary of replies or
    forward them my way?

    Thank you in advance,
    -Joe Seay (
    Dear Steve,

    Here are references to two algorithms used by other researchers:

    DiFabio RP (1987) Reliability of computerized surface electromyography for
    determining the onset of muscle activity. Physical Therapy, 67:43-48

    Bonato P, D'Alessio T, Knaflitz M (1994) A novel approach to the estimation
    of muscle on-off timing durting gait. Proceedings of the 1994 ISEK conference.

    We have implemented the DiFabio algorithm with limited success mainly
    because of the problems imposed by a muscle that is on all the time. The
    Bonato approach looks interesting in that it used more sophisticated signal
    processing techniques but I haven't had any experience with it.

    + Richard Smith e-mail: +
    + Head, Biomechanics Division, +
    + Faculty of Health Sciences, ,-_|\ +
    + The University of Sydney voice: +61 2 9351 9462 / \ +
    + East Street, Lidcombe, NSW 2141 fax: +61 2 9351 9520 \_,-._* +
    + AUSTRALIA v +

    Hi Steve,

    How are you and the planning of the NASGCMA conference ???

    I just read your posting about EMG onset and cessation...

    In March of this year a man named Leonard Caillouet posted a message asking
    for volunteers to mark onset and cessation times on some EMG files after
    they had been full wave rectified only or fwr and filtered at 6, 16, 39 Hz.
    I participated in the study and sent my marked onset and cessations to him.

    In August I wrote to him and asked for my results in comparison to others.
    He said he was not finished recruiting volunteers, but from the results he
    had observed thus far that increased filtering was increasing the
    variability of people indicating onset and cessation.

    He may still be looking for volunteers, or he may be ready to let you know
    more than I know. His e-mail address is:

    We had a really talented student in the lab last year who wrote some EMG
    processing software, that we gave to Edi Cramp, that he now distributes.
    The software has a level detector that will objectively indicate "on" or
    "off" based on a user specified % of maximum contraction during a gait cycle
    or some other maximum voluntary contraction.

    You can see the output of the program in our clinical case that we sent out
    to the interlab participants. If you want to know more about the software
    please let me know.

    I would really love to read what other people think about your posting ...

    Suzanne Halliday
    Texas Scottish Rite Hospital Gait Lab
    ph (214)559-7580