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  • Summary: Minimum muscle off set

    Hi


    Thankyou to all who contributed responses to my question about minimum
    periods of muscle inactivity. It's nice to know that there are a few
    people tackling the same hurdle.


    There are some useful references contained within the summary below.


    Again thankyou for your contribution.


    Cheers.



    Mick Dillon



    ORIGINAL MESSAGE

    _______________________________________________

    0000,0000,ffffGood afternoon.


    I am currently completing some software to analysed EMG data including
    muscle on/off times. This topic has received much attention both within
    the literature and Biomech-l postings but despite our best efforts
    remains a dubious practice.


    Periods of muscle activity have been determined in numerous ways. After
    much consideration I have chosen the following 2 criteria for my
    software.


    1. Mean resting level + 3 SD above that mean to define a resting
    threshold for each muscle.

    2. The muscle must remain 'on' for a minimum of ~50 m/s. This
    t-value has been specifically selected for each muscle
    analysed based on previous literature.


    My concern is that multiple bursts of activity which meet the above 2
    criteria are interspersed with very small periods of inactivity (about
    9-22 ms). The muscles most affected are Tibialis Anterior and Biceps
    femoris during late swing.


    I wish to set another test condition to examine the muscle 'off' times to
    alleviate this problem, but have been unable to find any literature to
    provide a physiological basis for a test condition.


    I hope someone may be able to point me in the direction of some further
    literature which defines the minimum period of muscle inactivity
    between contractions.


    Thank you in anticipation



    Kindest regards,




    Mick Dillon.




    RESPONSES

    _______________________________________________


    Michael:


    Probably the most comprehensive review of the subject is in:


    1. Hodges, P.W., & Bui, B.H. (1996). A comparison of computer-based

    methods for determination of onset of muscle contraction using

    electromyography. Electroencephalography and Clinical Neurophysiology,

    101, 511-519.



    You are correct that the end of an EMG burst is more difficult to

    determine. However, if you have clean EMG signals and a knowledge of

    how your EMG activity relates to kinematic events, you should be able
    to

    develop an efficient algorithm based on the combination of the two.

    Finally, it is important to develop a program that will allow you to

    manually correct the points selected by the computer algorithm should

    they be wrong.


    Best Wishes,


    David A. Gabriel

    __________________________________________________ ____


    Dear Mick,


    I had similar dilemma with determining muscle off times. I used the

    criterion for "off" that the muscle had to fall below the threshold for
    at

    least 100 msec in order to be considered off. The 100 msec duration
    was

    chosen subjectively based on the assumption that the activity I was

    investigating (muscle activity around initial contact of a stride of

    walking) was rather slow and that 100 msec would be between 10-15% of
    the

    cycle. I felt that if the muscle was inactive for that long then when
    it

    turned on again it was for another functional reason. I would have

    ignored the little blips in between since they would likely have little

    functional contribution to movement.


    Also, you might be using a threshold that is too low. I had to use a

    threshold of 2.5 times the resting value, not the standard deviation of

    the resting value. (we were using a telemetered system with rather high

    noise).


    I'll be interested in the summary of responses. Will you post them?

    Thanks.


    ************************************************** **********************

    Katy Rudolph, PhD, PT Ph: 617-353-5463

    Center for BioDynamics fax: 617-353-5462

    Department of Biomedical Engineering krudolph@bu.edu

    Boston University

    44 Cummington Street

    Boston, MA 01887


    ____________________________________________


    I think that you may go to find out a paper in literature:


    "Computer algorithms to characterize individual subject EMG profiles
    during

    gait," by Ross A. Bogey, Lee A. Barnes and Jacquelin Perry in

    Arch Phys Med Rehabil Vol.73, pp.835-841, Sept 1992.


    The paper would provide some interesting criteria which might fit to
    your

    interests.


    -----

    Szi-Wen Chen, Ph.D.

    Post-Doctoral Researcher

    1027 Dodd Hall

    Gait Analysis Laboratory, Department of Surgery

    The Ohio State University

    480 W. 9th Ave., Columbus OH 43210

    Tel: 614-293-4832

    Fax: 614-293-4834

    http://o2.gait.ohio-state.edu/chens

    __________________________________________________


    Mike-


    I read your post on the biomechanics list serve. Although I can't help

    you with the question you posted, I have an interest in the software
    you

    are developing to measure muscle onset. I am currently working on a

    project looking at reflex latencies to imposed joint perturbation at
    the

    ankle (an inversion perturbation device) as part of a larger
    investigation

    considering ankle sensorimotor characheristics. Several authors have

    reported with similar methodologies, however the exact methods utilized

    to determine muscle onset have varied. Several have reported extremely

    high reliability using several filters (high pass, low pass, followed by
    a

    smoothing filter) with either a visual inspection or 5SD above
    background

    noise to determine onset. In fear of introducing a bias through
    filtering

    and processing the EMG data too much I have tried using 5SD for a
    minimum

    of 50ms burst as the criteria for onset, however I have gotton
    incredible

    amounts of variablity between trials. I suspect that this may be
    related

    to several factors concerning the onset definitions, and other

    methodological considerations (number of trials being averaged for

    example). I am interested in any insight you may be able to share
    based

    on your experiences with the software development. Is your software

    appropriate for an application in reflex latencies? Thank you in
    advance

    for any insight. I will be traveling over the course of the next week
    so

    I may be away from email temporarily. Bryan




    Bryan L. Riemann, MA, ATC

    Doctoral Student

    Neuromuscular Research Laboratory

    University of Pittsburgh

    blrst15+@pitt.edu


    _________________________________________________-


    Michael,


    I am grappling with the same problem with EMG data from cervical muscles.
    I would appreciate receiving any information you gather on the topic.


    Regards,


    John


    --

    John Brault

    Biomechanics Research & Consulting, Inc.

    840 Apollo St., Suite 218

    El Segundo, CA 90245


    Phone: 310-615-3112

    Fax: 310-615-3038

    Email: john@brcinc.com

    http://www.brcinc.com/

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