Mechanomyography (MMG)

[Guest guest]

Some weeks ago I referred in one of my letters to the use of devices to

measure muscle tension indirectly, such as the myotonometer and the

mechanomyogram.

In the earliest days of drawing up my PhD proposal in the 1970s, I was

thinking of using mechanical methods for analysing muscle action during high

strength and power activities, so I considered a few different approaches

that were scarecely known in the world at the time. At the time I worked in

the Linguistics Dept at my university, where one of my colleagues whose

research with some very costly electrosonographic equipment examined the

sounds made by the human vocal tract. He most helpfully allowed me to use

this same apparatus to analyse " muscle sounds " (after I had read about this

phenomenon in the Scientific American), as well as the sounds made by our

joints (such as crepitus in the knees).

Around the same time I used to visit the obstetrics unit at one of the

hospitals where one of my colleagues there very kindly helped me carry out

ultrasonic analysis of muscle action. At the same time, one of my engineering

colleagues constructed a force plate system for me because there were zero

funds available for me to even think of buying such a system (the Kistler

systems at the time cost tens of thousands of dollars). My initial work on

that force plate system led me to shelve all the other preliminary muscle

sound and muscle ultrasonographic research and to decide on another topic

using the force plates to analyse the stability of the knee.

Anyway, the following letter from the Biomch-L list offers more useful

information on the mechanomyogram and shows how this approach has matured

since our earliest forays into this territory. Maybe I should have completed

my initial work in this field because it seems that it has only really

started to develop in quite recent times.

For information and archives of this most professional and useful list go to:

http://isb.ri.ccf.org/biomch-l

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I am very thankful for receiving so many responses to my enquiry regarding

MMG signals. Special thanks are to B, T Cramer, Edmund Cramp and

Ebersole. A summary of the answers follows below:

" Indeed one can use microphones or small acclerometers to recording VMG etc.

Dytran has miniature acclerometers but they are quite expensive, and we have

not yet got good data w/ that (but others have?). VTI Hamlin has quite

affordable accelerometers (around $50 if I remember correctly). These are in

forms of chips (e.g. SCA 610 series) so one has to glue them onto small

plastic bended pieces in order to get them oriented in the right direction.

With inbuilt amplifier they are very simple to use. Small electret

microphones can also be used (around a couple of euro a piece) As an

experiment we plugged a microphone into an ordinary stethoscope (cut off part

of the " tube " and inserted the microphone into the tube). Preferable one

should make a somewhat lighter " cup " for collecting the sound (amplifies the

air pressure that reaches the microphone) "

" Different nomenclature has been used to describe the mechanomyographic

signal (i.e., acoustic myography, vibromyography, sound myography, and

mechanomyography). We have chosen to use the term mechanomyography (MMG) in

our studies to be consistent with the suggestion of Orizio, C. (1993). Muscle

sound: bases for the introduction of mechanomyographic signal in muscle

studies. Crit Rev Biomed Eng, 21: 201-243. As you may already know, Dr.

Orizio's review is a very helpful source of information on a number of topics

regarding MMG.

Also, the review by Stokes, M.J. (1993). Acoustic myography: applications and

considerations in measuring muscle performance. Isokin Exer Sci, 3: 4-15 is

another helpful source. I am not familiar with any literature indicating that

the nomenclature is a function of the type of sensor used to record the

signal. Dr. Claudio Orizio's review, however, briefly discusses the different

terminologies used and provides a justification for the use of

" mechanomyography. "

There are two basic classifications of MMG signal acquisition units:

1. piezoelectric crystal contact sensors, and

2. accelerometers.

We use Hewlett Packard (HP) 21050A piezoelectric crystal contact sensors in

our laboratory interfaced through a BIOPAC acquisition unit and A/D

converter. Again, sensor differences and justifications for using either are

discussed to great extent in Dr. Orizio's review.

In addition, Dr. Watakabe has published several recent papers on the use of

different MMG sensors. The following reference is the most recent publication

of Watakabe et al. that I am aware of on this topic. Further references are

included in this paper. Watakabe, M., Mita, K., Akataki, K., and Itoh, Y.

(2001). Mechanical behaviour of condensor microphone in mechanomyography.

Medical & Biological Engineering & Computing, 39: 195-201. "

" Since the EMG and AMG signal bandwidths are relatively similar, I would

expect that almost any modern EMG system could be used. I am certain our own

system (Motion Labs MA-300 - http://www.motion-labs.com/emg.htm) would work. "

" As for the recording device, most are either using an accelerometer OR a

heart sound/pulse contact sensor made by Philips Medical Systems. Little is

know on the potential differences between the devices, but the results tend

to be the same...or at least interpretation of the results. Dan Barry

published a paper on using the MMG signal as a prosthetic control (Arch Phy

Med Rehabil 67:267-269, 1986) "

o de Oliveira Andrade

PhD student

University of Reading

Department of Cybernetics

Pepper Lane UK

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Dr Mel C Siff

Denver, USA

http://groups.yahoo.com/group/Supertraining/