Dear Riza,

It depends on what you are trying to accomplish. 

You can use the Borg percieved effort scale, if you don't need it in real-time and it doesn't need to be that sensitive. 

You can use myoacoustics, if for some reason EMG is not an option.

You can use things like output force, assuming the joint configuration doesn't change much. 

It's very application specific, if you can give more info about your application, you can get better feedback from us.

Regards

-Jack

I believe Jack is referring to mechanomyography (MMG), when referring to myoacoutics.  MMG has been referred to as acousticmyography and vibromyography in the older literature, prior to the consensus to call it MMG in 1993.  MMG would indeed show muscle activity, and does have benefits over EMG.  However, its reliability is still in question, as the relationship between MMG and force is not as repeatable as EMG and force.  It is still widely used though.  And since its less susceptible to noise, and the muscle has a basal, or resting tone to it, resting MMG levels are more useful clinically than resting surface EMG.

There are also medical imaging options, which could determine the on/off state of muscle based on blood flow, but may not be able to provide a reliable relative intensity (i.e. the level of force produced). 

Dear Jack and Jason,

Thank you for your interest. For my project, I would like to record activities of some muscles in the spine (and force if possible) at static postures or during motion like flexion and extension. The method should be applicable to use in-vivo. Do you think that myoacustics (MMG) can be used for my case? I will have a look at it.

Best regards,

Riza.

Dear Riza

Can I ask why you aren't interesting in using EMG? There are always tradeoffs to be made when comparing systems, and from your basic description I would have said 'EMG, definitely'.

Jason - you've made me feel quite old fashioned now. Now I need to consciously update my terminology.

Actually, I do not know much about EMG. But, as I heard, EMG may fail to produce accurate output when there is a motion. In addition, muscles in the spine could be very complex to apply this technique because of the fact that most muscles are grouped in layers. So, I wanted to know other methods if any would exist.

Riza, for the use of spinal musculature, I do think MMG might be a better way to go.  The resting activity of postural muscles may be difficult to discern from noise in a surface EMG signal, as the amplitude is fairly low.  A paper that comes to mind is

• Resting mechanomyographic amplitude for the erector spinae and trapezius muscles following resistance exercise in a healthy population.  Nathan P Wages et al 2013 Physiol. Meas. 34 1343

Jack, no worries. It hasn't quite caught on as some may have hoped. And it was actually 1995, but not widely known until Orizio 2003. Here is an excerpt from Travis Beck's MMG book:

• "At this point, it is important to acknowledge the fact that various terms have been used to describe MMG, including soundmyography, phonomyography, acoustic-myography, accelerometermyography, and vibromyography. Although the use of these terms was heavily influenced by the type of sensor used to detect the signal, it created confusion in the literature with regard to what was actually being measured. Thus, in 1995, the term “surface mechanomyogram” was suggested at a CIBA Foundation Symposium to distinguish the MMG signal from other mechanical signals that are unrelated to muscle activity (Orizio et al. 2003)."

However, not everybody is on board with this yet. I know BIOPAC Systems still markets their transducer as Vibromyography (despite the fact that they filter out a significant chunk of the useful signal).

Riza, I just saw your previous message. You should know that both EMG and MMG are susceptible to physiological cross-talk.  That means that if muscles are grouped too close together, it may not be possible to determine precisely which one is contracting.  This is especially true if the muscle is not superficial, as then it would almost certainly be contaminated by activity of more superficial muscles. 

Ok, now we get to the meat of the problem.

sEMG is problematic when looking at moving muscles, and even more so when you have multiple muscles overlapping each other. Plus you can have (even though these can be dealt with) motion artifacting in your data.

I, personally would advocate intramuscular EMG, but I have a well known bias that way. You can read up on the relative strengths of sEMG vs intramuscular EMG in

Perry et al. "Surface Versus Intramuscular Electrodes for Electromyography of Superficial and Deep Muscles" 

and look at some ways to deal with crosstalk or evaluate it from the following.

Farina et al. "Surface EMG crosstalk evaluated from experimental recordings and simulated signals. Reflections on crosstalk interpretation, quantification and reduction"

Solomonow et al 'Surface and wire EMG crosstalk in neighbouring muscles.'

Schorsch et al 'EVALUATION OF CROSS TALK BETWEEN ADJACENT MUSCLES IN FELINE EMG RECORDED USING IMPLANTABLE MYOELECTRIC SENSORS' 

Good luck

Dear Jason and Jack,

Thank you for your useful comments and recommendations for further reading.

Best,

Riza.

Dear Riza,

I read the comments above, and I would suggest you to use multichannel surface EMG with some large bidimensional array of electrodes in order to reduce movement artifacts and crosstalk (by applying some spatial filter for instance). I would not suggest to use MMG in dynamic conditions because the interpretation of the results is more difficult. In addition with sEMG you could compute some additional parameters like muscle fiber conduction velocity.

best regards

Corrado

I am afraid you will not be able to get rid of the crosstalk, so I would recommend aiming at recording from muscle groups rather than from individual muscles. Also you should consider building the preamplifiers integrated with electrodes (EMG) or microphones (MMG). If you add appropriate filters, you can easily get rid of motion artifacts.

There is another technique, tensiomyography. This non-invasive method is useful to measure muscle activity, muscle contractility, among other things. It is a simple tool to use but only in static not in dynamic movement.

Best

Riza,

  I think EMG will be your most logical solution.  Surface EMG is easier, but indwelling or fine wire EMG get closer to what you're looking for.  There are many methods to eliminate noise and crosstalk included shielded, amplified electrodes, and careful electrode placement along with various filtering methods.  I recommend you find an EMG expert at your university and consult with them how best to approach this task. 

Good luck.

Dear Micah

Spinal intramuscular EMG is quite literally a pain in the neck. I like it, alot, though, especially if you really need to get individual muscle activities. But, you need a fairly well trained person to get you through your IRB typically. 

I usually advocate for using surface EMG first, then going to fine wire only when individual discrimination is really needed. 

-Jack