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kirtley24
06-12-2005, 10:30 PM
Dear all,

Summertime is always a good time for thinking about things that we
somehow never got round to figuring out. One of these is
electromechanical delay. As you know, every muscle contraction is
accompanied by an electrical phenomenon (myoelectric response), which
can be detected by surface or indwelling electrodes as the EMG.

The question I want to ask is whether there is any time delay between
these two events? This might sound obvious when you think of the raw
EMG, but I have always followed David Winter's reasoning that EMG
should always be smoothed at a frequency related to the twitch time of
the muscle (usually about 3 Hz for lower-limb muscles) so that its
envelope most closely matches the force generated by the muscle.

When this is done, I think I am correct in saying that there will be
no electromechanical delay, since the pattern of EMG and force will be
virtually the same. I know that some people smooth at a somewhat
higher frequency (10-20 Hz), at which the delay between electrical and
mechanical response is noticeable (anything from 30-100 ms). But it
seems to me that this is a rather arbitrary result, which is simply a
function of the filter cutoff.

So, my questions are:

1. Is there, in fact, such a thing as electro-mechanical delay?
2. If so, how should it be defined?
3. What is it for common muscles?

I look forward to your thoughts!

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
Dept. of Biomedical Engineering
Catholic University of America
Washington DC 20064

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