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Re: cocontraction questions

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  • Re: cocontraction questions

    Several months ago I requested information on the "common drive" explanation
    of increased antagonist activity with agonist muscle fatigue and differences
    between EMG from isometric exertions resisting gravity-assisted loads vs.
    EMG from isometric exertions performed against a locked dynamometer. Here
    is the original posting followed by a summary.

    Dan Kelaher wrote:

    > Researchers,
    > I have two questions that I haven't found answers to in my lit
    > searches. I hope someone out there can help me. I am interested in
    > cocontraction increases with agonist fatigue, specifically in the trunk
    > muscles.
    > 1. I have read two explanations of increased cocontraction with agonist
    > fatigue. The first is stability suggested by Kellis et al on the knee
    > and Potvin et al on the trunk. The second explanation is the "common
    > drive theory" by Psek and Cafarelli for which I can find no direct
    > follow up articles. Does anyone have any further information on the
    > explanation of increased cocntraction with agonist fatigue or any
    > furtherresearch related to the "common drive theory" as it applies to
    > cocontraction and fatigue?
    > 2. In one experiemnt I am planing to do, I have to decide whether to
    > use gravity-assisted loading (eg, free weight type of loading) or
    > non-gravity-assisted/more controlled loading (eg, Kin-Com dynamometer).
    > These exertions will probably be isometric. Does anyone have any
    > thoughts/research findings related to the differences between these two
    > types of loading conditions? I have a suspicion that they may yield
    > different levels of cocontraction and agonist EMG levels.
    > Any thoughts on these questions would be very much appreciated. I will
    > post a summary of the replies after I receive them. Thanks.
    > Dan Kelaher
    > NCSU Ergonomics Lab

    I only received a couple of responses on these issues, one who asked to
    remain anonymous and one from Dr. John Rasmussen PhD,
    (, The AnyBody Group, who
    has shown numberically the advantages of antagonism in the squat lift
    (papers in PDF format at his web sites).

    My primary knowledge on the common drive theory came from sources like
    Muscles Alive and other DeLuca papers (among others) that have tested the
    common drive primarily in the upper extremity muscles. Others have looked
    at this in the thigh (another Cafarelli paper) and the low back. I
    appreciate the help from the respondents on this question.

    I received no feedback on the second issue so I decided to just go ahead
    with the pilot study for my research. Results are not available yet since I
    have not collected or analyzed all the data.

    Thank you again.

    Dan Kelaher
    NCSU Ergonomics Lab

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