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jives38
06-15-2005, 12:07 AM
Biomecher's

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
registered.

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

Jeff Ives

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

jives@ithaca.edu
607-274-1751