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Jaime B. Zamora S.
07-09-2000, 08:40 AM
Here is the answers to the post.
Thanks to all.

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Original message:
Dear coleagues.

I've seen in many articles expressions like average rectified value, mean
power frequency, but I've not found math expressions for this algorithms.

There is information available in this topic?

Thanks in advace.

PD: I'll post a summary if i receive replies
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Jaime,

These articles should adress your questions. These equations are also in
the Basmajian & DeLuca book.
a.. Basmajian, J.V. and C.J. DeLuca. Muscles alive: Their functions
revealed by electromyography. 5th rev. ed., Baltimore, MD: Williams &
Wilkins, 1985, pp. 60-64.
b.. Bilodeau, M., Arsenault, A., Gravel, D. and Bourbonnais, D.: EMG power
spectrum of elbow extensors: a reliability study. Electromyogr. Clin.
Neurophysiol., 34: 149-158, 1994.
c.. Heinonen, A., Sievänen, Viitasalo, J., Pasanen, P., Oja, P. and Vuori,
I.: Reproducibility of computer measurement of maximal isometric strength
and electromyography in sedentary middle-aged women. Eur. J. Appl. Physiol.,
68: 310-314, 1994.
Best Wishes,

-d.g.

David A. Gabriel, Ph.D.
Assistant Professor
Biomechanics
Physical Education Department
Brock University
St. Catharines, Ontario, CANADA
L2S 3A1


Phone: 905-688-5550 ext.4362
Fax: 905-688-5550 ext. 4104

e-mail: dgabriel@arnie.pec.brocku.ca
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Dear Jaime:

Rectification means to take the absolute value of the EMG signal. A
Fourier transformation is required to look at the EMG power spectrum. Any
basic textbook on signal processing (or talk to someone in electrical
engineering) should have the information on how these quantities are
calculated.

Sincerely,

John


At 10:48 AM 6/7/00 -0400, you wrote:
>Dear coleagues.
>
>I've seen in many articles expressions like average rectified value, mean
>power frequency, but I've not found math expressions for this algorithms.
>
>There is information available in this topic?
>
>Thanks in advace.
>
>PD: I'll post a summary if i receive replies.
>
>Jaime B. Zamora S.
>Laboratorio DAMAC.
>Departamento de Ingeniería Mecánica.
>Pontificia Universidad Católica de Chile.
>http://www.ing.puc.cl/icmtesis/magister/jzamora/jzamora.htm
>
>Attachment Converted: "E:\Attach\Jaime B. Zamora S..vcf"
>


John M. Barden, M.Sc. & Rehabilitation Technology Dept.
Ph.D. Candidate Glenrose Rehabilitation Hospital
Surgical-Medical Research Institute 10230-111 Ave.
Department of Surgery Edmonton, Alberta
Faculty of Medicine & Dentistry T5G 0B7
University of Alberta Work phone: (780)471-2262 ext. 2688
Edmonton, Alberta Fax: (780)471-7972
Canada T6G 2E2 e-mail: jbarden@ualberta.ca &
rara@dlcwest.com
---------------------------------------------------------------------------
Dear Jaime:

Rectification means to take the absolute value of the EMG signal. A
Fourier transformation is required to look at the EMG power spectrum. Any
basic textbook on signal processing (or talk to someone in electrical
engineering) should have the information on how these quantities are
calculated.

Sincerely,

John


At 10:48 AM 6/7/00 -0400, you wrote:
>Dear coleagues.
>
>I've seen in many articles expressions like average rectified value, mean
>power frequency, but I've not found math expressions for this algorithms.
>
>There is information available in this topic?
>
>Thanks in advace.
>
>PD: I'll post a summary if i receive replies.
>
>Jaime B. Zamora S.
>Laboratorio DAMAC.
>Departamento de Ingeniería Mecánica.
>Pontificia Universidad Católica de Chile.
>http://www.ing.puc.cl/icmtesis/magister/jzamora/jzamora.htm
>
>Attachment Converted: "E:\Attach\Jaime B. Zamora S..vcf"
>


John M. Barden, M.Sc. & Rehabilitation Technology Dept.
Ph.D. Candidate Glenrose Rehabilitation Hospital
Surgical-Medical Research Institute 10230-111 Ave.
Department of Surgery Edmonton, Alberta
Faculty of Medicine & Dentistry T5G 0B7
University of Alberta Work phone: (780)471-2262 ext. 2688
Edmonton, Alberta Fax: (780)471-7972
Canada T6G 2E2 e-mail: jbarden@ualberta.ca &
rara@dlcwest.com
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Dear Jaime, you are right, these formulae are usally assumed
familiar. A good text is in the (very recent) book : SENIAM
recommendations for surface electromyography, Ch 3
published by Roessingh RRD ISBN 90-75452-15-2
see also a webpage at
http://www.delsys.com/emg_articles/EMG.shtml#processing
But this page does not give formulae either. so I give them:
It is a bit awkward without the right symbols.
average rectified:
-filter(abs(raw emg))
filter can be moving average, Butterworth etc. low pass
for dynamical movements I would recommend a cut-off frequency of 20
Hz

mean power frequency
- make power spectrum S(f) by FFT over some epoch T
- MPF = int( f*S(f))/int(S(f) with int from 0 - inf
- Median freq = fm
, so that int from 0-fm (S(f)) = 0.5* int from 0-inf (S(f))

if you really want formulae on frequency parameters (an awfull lot in
fact) , consult my paper in IEEE trans BME 38:1077-1088 (1991).
Good luck

At Hof
Department of Medical Physiology &
Laboratory of Human Movement Analysis AZG
University of Groningen
A. Deusinglaan 1
room 769

PO Box 196
NL-9700 AD GRONINGEN
THE NETHERLANDS
Tel: (31) 50 3632645
Fax: (31) 50 3632751
e-mail: a.l.hof@med.rug.nl
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--

Regards,

http://www.ing.puc.cl/icmtesis/magister/jzamora/index_esp.html
Jaime B. Zamora S.
Laboratorio DAMAC.
Departamento de Ingeniería Mecánica y Metalúrgica.
Pontificia Universidad Católica de Chile.


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