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Re: Nova BM literatura

From: BM literatura z ledna 2000
Date: 1.2.2000
Time: 10:03:21
Remote Name: 195.113.14.94

Comments

Thanks much to all those who replied to my message regarding running and EMG collection.

Posted below is the original question and the replies I received. A combination of techniques has resulted in a better signal.

Thanks again,

Sean Keegan

########################## Original Posting:

I am attempting to capture EMG data from the vastus medialis/ vastus lateralis/ tibialis anterior while running (2000Hz sampling). My problem is that there seems to be a movement artifact just prior to EMG activity of the leg - it looks like foot-contact is producing the artifact. Has anyone else found this type of signal response during a running movement and/or the best ways to avoid this problem?

I am collecting using typical surface EMG techniques (hair removal, skin abraision, etc) but due to the type of electrode (TSD150B) I am not using conductive gel. ###############################

However, we have had the best luck reducing movement artifact when using double-stick foam tape (approx 2 mm thick, with holes slightly smaller than the electrode surfaces), filling those holes with conductive gel, and NOT using any other tape or wrapping over the top of the electrode. I think the gel-filled "wells" in the foam tape help to eliminate artifacts caused by movement of the electrode relative to the skin. We do tape the wire to the subject proximal to the electrode to avoid any stress on the electrode, but have found that any tape or wrapping that actually goes over the electrode seems to contribute to movement artifact.

If what you're seeing is mechanical artifact due to foot contact, you should be able to reproduce it by having the leg propped up and relaxed and then whacking on the bottom of the foot. If that doesn't reproduce it, you could try tapping near the electrodes or leads to see if that reproduces what you've been seeing. If you have been taping or wrapping over your electrode, I think it's possible that changes in the pressure applied by the wrap (e.g. due to hamstring muscle activity prior to heel contact) could cause some artifacts.

Good luck, Greg

################################### As to your motion artifact. Those electrodes have a fairly large mass especially compared to the size of the medialis so it's easy for mechanical artifact to occur between the electrode and the skin. I don't know what type of precautions you're taking with ahdering the electrode, but some of your artifact may go away if you loop the leads near the electrode and tape (or wrap) them down. I suspect that you'll not get rid of all the artifact, and then your only choice is to filter out what you can.

Motion artifact is typically low frequency, so you can either high pass filter your data with a cutoff of 10 Hz, or even as much as 20 Hz, as there is arguable NO real EMG down in that frequency range. Or bandpass your data with cutoffs such as 20 and 250. I may be suggesting things that you've already tried, but if not take a look at some raw data after filtering and see if that didn't get rid of most of the problem. A little filtering and a little caution with how the electrodes are attached should take care of it.

good luck

Tim

=========================================================== Timothy S. Hilliard, Ph.D. ofc: (617) 373-5994 Assistant Professor fax: (617) 373-3161 Physical Therapy Dept. e-mail: thilliar@lynx.neu.edu 206 Dockser Hall Northeastern University Boston, MA 02115

################################## I have would suggest trying a different electrode type just to see if you get any differences (I assume the ones you are using are the disposable type). I would not use the biopac standard surface electrodes (at least those from a couple of years ago) -- we have found them to not stick well. We use electrodes from sensormedics.

Alternate explanations could be some sort of static discharge upon contact (unlikely perhaps), or when the leg is in a particular position or on heel strike the artifact comes from cable movement and not tissue movement.

Good luck, Jeff -- Jeff Ives, Ph.D. Dept. of Exercise & Sport Sciences Phone: 607-274-1751 Ithaca College Fax: 607-274-1943 Ithaca, NY 14850 USA Email: jives@ithaca.edu #####################################

If it is a movement artifact then it should be at a low frequency relative to the EMG, so you should be able to filter it out using matlab or a similar program. Dr Jim Richards Health Care Professions University of Salford Salford M6 6PU UK #######################################

Sean Keegan Biomechanics Graduate Program Asst. Coach Men's Track and Field Ball State University

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Last changed: únor 01, 2000