Garry:
Thanks for a thought-provoking response to my
original posting.
> My opinion may also be confused but..
>
> The concept of EMG <=> strength is a can of worms.
>
> You may wish to consider the term "muscle performance" this
> refelcts all forms of function including the tests which result in
> 'strength' scores.
I rather like your term "muscle performance"; I will
try to use it in sentences in the future and see if it
holds up. My alternative so far has been "functional
strength", which I think intends the same thought.
> Another example of this problem is when we try to amplitude
> normalise trunk
> muscle activity during tasks where the individual has had limited
> experience or it is possible that pain (i.e low back pain). In most
> clinical situations both conditions are true for a MVIC .
Interesting parallel. We certainly find patients
have "limited experience" in using their pelvic
muscles.
> The relationship between EMG amplitude and improvements in muscle
> performance (strength) is also interesting. The early work
> by DeVires (1974
> I think) and Moritani & DeVries (1979) provide a ratio of
> improvement
> partialling out central (drive / neurogenic) and peripheral
> (hypertophy)
> mechanisms. Such a theory suggests that the large early (<4
> wks) changes in
> muscle performance following resistance training are neurogenic.
I'm not sure what "neurogenic" means in this context
but it certainly sounds like you are saying that
improvements in the entire CNS function are
involved in those large early changes -- with
which I would agree.
> As for using EMG amplitude to quantify a skill (motor
> control task) - I
> believe that the variability in the motor pattern tells you
> as much if not
> more than certain derived amplitude parameters.
Interesting observation. Howard Glazer's work on
Vulvodynia focused on minimizing the standard
deviation of the pelvic floor muscles at rest.
In the early days of biofeedback (before computers),
we developed a "ten-second hold test", which was the
RMS average of all ten seconds in a 10-second
window of opportunity designated for a contraction.
Obviously, any variability in this maximal effort
resulted in lower "scores". Now, with computers,
we can get the s.d. of the contraction, but no one
has gathered any systematic data on this.
One form of "validity" is "predictive validity".
The first study of the predictive validity of pelvic
muscle EMG measurements found low readings
could reliably and repeatedly predict incontinence
problems. [Glazer et al, J. Repro. Med., 1999]
> As for Biofeedback and strength- the greatest
> changes occur between the
> ears no matter where you put the electrodes :-)
That may be so, but such changes are usually
very difficult to measure; that's why we use
peripheral measures. But I appreciate your
observation!
>
>
> cheers
> Garry.
Thanks for the suggestions.
John Perry, PhD
>
> see <http://www.ncbi.nlm.nih.gov/entrez/>
>
> Moritani T. Neuromuscular adaptations during the
> acquisition of muscle
> strength, power and motor tasks.
> J Biomech. 1993;26 Suppl 1:95-107. Review.
> Ishida K, Moritani T, Itoh K. Changes in voluntary and
> electrically
> induced contractions during strength training and
> detraining. Eur J Appl
> Physiol. 1990;60(4):244-8.
> Moritani T, deVries HA. Potential for gross muscle
> hypertrophy in older men.
> J Gerontol. 1980 Sep;35(5):672-82.
> Moritani T, deVries HA. Neural factors versus hypertrophy
> in the time
> course of muscle strength gain.
> Am J Phys Med. 1979 Jun;58(3):115-30.
>
>
> Allison GT, Godfrey P, Robinson G. EMG signal amplitude
> assessment during
> abdominal bracing and hollowing.
> J Electromyogr Kinesiol. 1998 Feb;8(1):51-7.
> O'Sullivan PB, Twomey L, Allison GT. Altered abdominal
> muscle recruitment
> in patients with chronic back pain following a specific exercise
> intervention.
> J Orthop Sports Phys Ther. 1998 Feb;27(2):114-24.
>
>
>
> ________________________________________________
> Garry T Allison (A/Professor of Physiotherapy)
> The Centre for Musculoskeletal Studies
http://www.cms.uwa.edu.au/
Department of Surgery, The University of Western Australia.
Level 2 Medical Research Foundation Building
Rear 50 Murray Street
Perth Western Australia 6000.
email <[log in to unmask]>
ph: (618) 9224 0219
Fax (618) 9224 0204
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