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Charles Allen
03-25-2004, 06:21 AM
Thanks again to all of those who responded to my question. The responses are posted below.


Charles,
I don't see a problem of using the isometric contraction to normalize
the non-isometric contraction. But you should be aware of the
possibility that you can get an EMG level during the dynamic contraction
that is >100% of the EMG level during a maximum isometric contraction
(so don't think that such an observation is a mistake). This was
observed in references 1 & 2, and mentioned as the Hof 1984 reference on
pg 374 of ref #3. Reference #4 is a potentially useful article on this
normalization topic.

GC

1: Swanson SC, Caldwell GE.
An integrated biomechanical analysis of high speed incline and level
treadmill
running.
Med Sci Sports Exerc. 2000 Jun;32(6):1146-55.
PMID: 10862544 [PubMed - indexed for MEDLINE]

2: Jacobs R, van Ingen Schenau GJ.
Intermuscular coordination in a sprint push-off.
J Biomech. 1992 Sep;25(9):953-65.
PMID: 1517272 [PubMed - indexed for MEDLINE]

3: Kamen G, Caldwell GE.
Physiology and interpretation of the electromyogram.
J Clin Neurophysiol. 1996 Sep;13(5):366-84. Review.
PMID: 8897204 [PubMed - indexed for MEDLINE]

4: Yang JF, Winter DA.
Electromyographic amplitude normalization methods: improving their
sensitivity
as diagnostic tools in gait analysis.
Arch Phys Med Rehabil. 1984 Sep;65(9):517-21.
PMID: 6477083 [PubMed - indexed for MEDLINE]



************************************************** ******************
Gordon Chalmers, Ph.D.
Dept. of Physical Education, Health and Recreation
Western Washington University
516 High St.
Bellingham, WA, U.S.A.
98225-9067
http://www.ac.wwu.edu/~chalmers/
Phone: 360-650-3113
Email: Gordon-dot-Chalmers-at-wwu-dot-edu
in above email address: replace "-dot-" with "."
replace "-at-" with "@"


We in the past have used a Cybex isokinetic dynamometer to get maximum
voluntary dynamic contractions - however this in itself has validity
problems, especialy when used for trunk movements because of the difficulty
isolating abdominals from hip flexors etc. Sorry not to be much help.
Su

Dr.Su Stewart
Division of Psychology and Sport Sciences,
Northumbria University,
Wynne-Jones Centre,
Newcastle Upon Tyne,
NE1 8ST
UK
Phone 0191 227 3712


Max contraction may be most stable for lower limb muscles. See
a.. Soderberg GL, Knutson LM. A guide for use and interpretation of kinesiologic electromyography data. Phys Ther. 2000 May; 80(5):485-498. [Review article.]
b.. Knutson LM, Soderberg GL, Ballantyne BT, Clarke WR. A study of various normalization procedures for within day electromyographic data. J EMG & Kines. 1994;4(1):47-59.


Loretta M. Knutson, PhD, PT, PCS
Professor, Physical Therapy
Southwest Missouri State University
email: LorettaKnutson@smsu.edu
phone: 417/836-8728 or 836-6128
fax: 417/836-6229


I have a couple of references that may be of assistance. The first is
related to normalization in general by Burden and Bartlett, 1999 Med
Eng and Physics 21:247-257. and the second is by Burden et. al.,
2003, J of Electromyography and Kinesiology 13:519:532. The
former discussed the value of isometric normalizations and the
latter re-examines different normalization procedures illustrating the
value of different procedures depending on the question being
asked. This is key.
Specific to abdominals are papers by:
S. McGill 1991, Journal of Orthopaedic Research 9:91-103 in which
he illutrstaed that different subjects recruited maximal activity from a
muscle using different exercsies thus a variety of exercises should
be used when normalizing to maximums. We (Vezina and Hubley-
Kozey 1998 Preceedings of NACOB, 401-402) also showed that
different exercises elicited maximums from different muscles for
different subjects so including more than one exercise per muscle
was important. A follow-up proceeding of ISEK, 2002 (Hubley-Kozey
and Vezina) discussed the importance of using an algorithm to
determine a window in which maximal activity occurred for each
muscle indiviudually since different subjects produced maximums
from different muscles at different times throughout a three-second
static contractions. Thus selecting the middle one-second for
example, as is often done will not always capture the maximal
amplitude. Applications of this approach are found in two papers on
abdominals Vezina and Hubley-Kozey, 2000 Archives of Phys Med
and Rehab 81:1370-1379 and Hubley-Kozey and Vezina 2002
Archives of Phys Med and Rehab 83:1100 -1108 which attempted to
relate amplitudes to a physiologic reference. Lehman and McGill
1999 J Manipulative and Phy Ther 22:444-446 discuss the
importance of normalizing in this context.
If evaluating phasic patterns then normalization as per Yang and
Winter 1984 is an approach as was done for abdominals in Hubley-
Kozey and Vezina 2002, Clin Biomechanics 17:621-629 .
If attempting to relate to modelling force you might want to check
out Marras 2001 (two papers) in J Electromyography and
Kinesiology.
Hope this helps.
Regards
C. Kozey


Dr. C. Kozey
Professor
School of Physiotherapy
Dalhousie University
Halifax NS
B3H 3J5



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