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Electromechanical Delay

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  • Electromechanical Delay


    There is a large body of literature on electromechanical delay (EMD) in
    the motor behavior/cognitive psychology literature; only it is referred to
    as motor time. Large numbers of studies, starting in the 1960's, began
    using EMG during reaction time experiments in order to fractionate the
    reaction time into the central processing component (premotor time) and
    the peripheral delay component (motor time or EMD). Most of these studies
    used "raw" EMG, and most were done using arm/hand muscles. 40-50 ms seems
    to be a common EMD, but in these studies measuring the mechanical part of
    the EMD can be a confounding factor.

    Measuring the onset of mechanical output varies widely depending on what
    one is measuring (e.g., isometric force, acceleration) and the sensitivity
    of the equipment. Certainly, measuring the delay between biceps b. EMG and
    the mechanical response of elbow flexion as measured by a strain gauge
    attached to a wrist cuff is different than measuring the EMD in an
    isolated frog muscle strung up on a force transducer, which is different
    from a microscopic view of actin-myosin cross-bridge formation following
    electrical stimulation.

    So, is EMD a real phenomenon? Most certainly yes, but the cause of the EMD
    may vary depending on what one is measuring. At the microscopic level, EMD
    may be very short and be based largely on Ca++ channel kinetics, time for
    cross-bridge formation, and so forth (others have described this much
    better than I can do). At the whole body level, the majority of the EMD
    may come from slack in the musculotendinous system and the time needed to
    develop large amounts of force before a mechanical response can be

    In sum, defining EMD for particular applications -- from basic
    physiological processes to clinical applications -- would seem to have

    Jeff Ives

    Jeff Ives, Ph.D.
    Associate Professor
    Dept. Exercise & Sport Sciences
    Center for Health Sciences
    Ithaca College
    Ithaca, NY 14850