Laurie's Blogs.

 

03
Dec 2022

Acoustic Myography in Dogs

Laurie Edge-Hughes, BScPT, MAnimSt, CAFCI, CCRT

 

Perhaps you’ve seen this paper come across your feed on Facebook.  Perhaps, like me, you thought, “What the heck is this?”  Perhaps you even downloaded the paper and have been waiting for an opportunity to read it.    Well, a long plane ride with no wi-fi and no inflight entertainment prompted me to actually read (and report on it)!  Here we go!

 

What paper am I talking about?

Harrison A, Fenger C.  The application of acoustic myography in canine muscle function and performance testing.  SOJ Vet Sci 3(1): 1-6.

 

What is acoustic myography? 

“Acoustic Myography (AMG), which directly measures muscle contractions, was recently documented as being a useful diagnostic tool for rapidly determining muscular injury in the veterinary clinic.”  (This from papers in 2013 and 2017).   When muscle fibers contract, they generate vibrations, and whilst, muscle fiber contractions are not always visible, they do vibrate in active muscles, and as such produce pressure waves, which can be recorded at the level of the skin above a muscle of interest – this is the principle behind acoustic myography, the recording of pressure waves from active muscles transdermally.    

 

(So, it’s like Electromyography, but measuring vibration versus electrical activity of the muscles.)

 

Methods:

In a nutshell, the authors evaluated 12 Labrador Retriever gaited by their owners, mostly outside (all but one) with the measuring portion of the device stuck to skin (shaved of hair) over the superficial gluteal and the longissimus lumborum muscles.  They took measurements at a walk and a trot (and the transition between walk to trot).

 

The Acoustic Myography Recordings

I’m going to admit, this is where they lost me a bit.  They looked at 3 different factors within the recordings of the device: 

 

“The E-score represents the period of time a muscle is active relative to periods of inactivity for a set recording interval. The S-score is determined as the signal amplitude in relation to a full 6dB signal. Finally, the T-score is determined as the frequency in relation to a Max T value.”

 

So, with my mind muddled with what that meant, I simply jumped down to the Discussion portion of the paper in an attempt to make sense of the Results.

 

A change in gait results in a decrease in muscle efficiency/coordination with the change in pace, but that there is a slight increase in fiber recruitment to match the increase in force needed to change pace from walk to trot. Perhaps the most interesting finding, however, is that trotting is associated with a lower fiber firing frequency (26-33%) than walking.

 

The lower E-score found in this study with a change of gait from walk to trot therefore illustrates an increase in the active phase of muscle contraction with this gait, commensurate with a transition towards elastic energy storage within the muscle.

 

Furthermore, the significant reduction in the frequency of contraction (increase in T-score) in both m. gluteus superficialis and m.longissimus lumborum with a transition from walk to trot also conforms to the idea of stored elastic energy. A reduction in active muscle contraction from 48% of the stride period to just 27% when going from the walk to the trot must surely serve to reduce muscle work.

 

The Take Aways?

Well, in addition to what is stated above (which is really something we would suspect all along…), the authors noted that the Acoustic Myography technique is a promising non-invasive method to assess muscle function changes related to elastic strain energy adaptations in muscles.  

 

(I presume we will hear more about this technology in the future.)

 

That’s it folks!

Until next time… Cheers!

Laurie

 



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