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Re: Linear enveloping of EMG

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  • Re: Linear enveloping of EMG

    Dear All,

    I think this discussion of the technical aspects of linear envelope (LE)
    processing of EMG is very interesting. However, it is important to not lose
    sight of the purpose of calculating the LE. It is designed to emulate the
    force development over time in the muscle. Thus, the low pass filter
    cut-off should be such to match the twitch characteristics of the muscle
    being studied. I believe that Winter has some data in one of his textbooks
    (sorry, can't recall which one at this point in time) that gives examples of
    appropriate cut-offs for slow twitch, fast twitch and mixed muscle. The
    range was around 1 to 2.5 Hz, I think. This would seem to suggest that 10
    Hz in the original email would be far too high. Also, if one is using, for
    instance, a Butterworth-type filter, it should be a second-order, critically
    damped one. In the end, with the appropriate choice of cut-off and damping,
    you should be able to have a reasonable estimate of the shape of the muscle
    force-time curve and it will account for the electro-mechanical delay as
    well.

    Cheers,

    Drew Smith, PhD

    Assistant Professor
    Department of Rehabilitation Sciences
    The Hong Kong Polytechnic University
    Hung Hom, Kowloon
    Hong Kong SAR

    Voice: +852 2766 7094
    FAX : +852 2764 1435

    http://www.rs.polyu.edu.hk
    rsdrew@polyu.edu.hk

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