EMG Testing does it tell all?

With EMG testing can you tell exact muscles and ranges of motion?

By Fred Koch, P-SCE

Lately the media in the fitness and sports industry seems to have become a “What is the Research” based system.  Well, I am one of these guys maybe it’s from my police background that says. “So you are telling me that all that has been said in fitness and sports has been discovered?” So, in line with that it also says all the research that has been done is legimate scientific research. If you think the same way I do my answer is NO WAY.

1.  To even ask the question “what does the research say?” is based on the 1^st premise there is nothing new.
2. In the fitness and sports industry you are telling me the research is all “real research”. Well anyone into research can give you a hundred reason that is wrong, when they stop laughing about the statement about fitness and sports research.

One piece of this pie, is about is the EMG testing. It seems EMG testing has become the “prove all” of muscle research. Well, I admit I am not be the smartest guy in the world and really am just a simple street guy, but something has always bothered me about this and maybe some of you can help me with it or maybe you will ask the same questions after you see what my curiosity stems from.

It is said there are two kinds of EMG in widespread use: surface EMG and intramuscular (needle and fine-wire)

Wikipedia

1. You use electrodes on the skin and test the muscle stimulation.
2. You put needles into the muscle and see what is the stimulation. That means sticking those needles  deep into the body to find the insertion and origin of the muscle. Ouch, Then you could tell which muscle was working and through what range of motion.
   

   Ouch, Incert what into my body?

The surface EMG is what I have questions.

1. You put electrodes on the skin, over top of a “focus” muscle, but also many other muscles in the area.
2. You do the exercise through a perceived range of motion.
3.  You get a reading.

Since the reading is one the skin,

1. How do you tell if the muscle in questin was being directly stimulated.

2. Was it stimulated as part of a compound movement.

3. Most of all how can you tell if the focus muscle was stimulated during it’s full range of motion. This to me is the main factor. How can you tell if this muscle is stimulated through a full range of motion.

You see from surface electrodes it seems you can get a reading, but if other muscles are helping out than how are you to tell how much they worked.

My street view is that is you can tell there was some activity in the area, but not where exactly it came from or was it through the full range of motion of the muscle. So what you were actually measuring is electric activity.

Again admitting I am not a rocket scientist I figured I would ask some of my friends that know more about this.

William A Sands, PhD,  surely one of the most noted people in the strength training world just happened to do his dissertation on EMG. Had this to say.

EMG is a useful tool, but like all tools you need to know its limitations.

I did my dissertation on EMG.  EMG is extremely useful for:
1.  Knowing which muscle(s) are active
2.  Knowing when muscle(s) are active

However, after that it gets a little dicey.  There is a nice linear relationship between magnitude of EMG and muscle force, but the relationship is only valid for isometric tension.  This is because the detection area under the electrodes changes (somewhat even in isometric settings), especially during dynamic movement as the muscle slides under the skin.  As such, we can use EMG to scale different muscle activation levels to the maximum seen during a skill, or to a maximal voluntary contraction; but again you can run into definitional problems like what is “maximal.”

You can use EMG to detect a shift to fatigue, but again, it’s most accurate in isometric settings.

I wouldn’t describe EMG as worthless, but the research question has to be carefully spelled-out so that you know whether EMG’s limitations are up to the task of providing unambiguous answers to your question.
In a further discussion:

I don’t know of any tool that is an “end-all.”  All tools have specific uses and when used “off-label” are usually less ideal.  Most research instrumentation has a list of limitations and delimitations.  I happen to really like EMG, but I also know that EMG is limited by a number of things:

1.  Electrodes and cables can sometimes get “in the way” during dynamic movement.
2.  Obviously, wearing EMG electrodes during competition is unlikely, so you’re forced to use simulations and laboratory settings.  Thus, ecological validity suffers.
3.  The EMG signal is the algebraic sum of positive and negative signals and usually underestimates the actual muscle activation signal being detected.
4.  Muscle crosstalk can occur in which local muscle signals can intrude on the signal/muscle of interest.  Sometimes filtering of the signal(s) can be used, but it can be difficult to tease out the specific signal of interest.
5.  Indwelling, needle, or wire electrodes are better for finding out what’s going on closer or in the muscle itself, but it’s invasive, painful, and very difficult to use in dynamic movements.
6.  While EMG is not staggeringly expensive, it’s also not cheap.  A number of approaches have been brought to market in recent years, telemetered electrodes (reducing or eliminating the problem of cables), but if you already have an EMG, you probably need to do a lot of EMGs to justify buying another one.

I’ve used EMG a lot in gymnastics.  Often, all I want to know is which muscles are active and when.  If I want to know more about the magnitude of activation of specific muscles then I struggle with how to scale the muscle activation(s) to force, or to other muscles to see a ranking of muscle activation.  Sadly, comparing across muscles is very difficult without some scaling or baseline indicator.

I’ve used EMG a lot in assessing why running and walking technique maybe eliciting pain and disability in broken runners and others.  Usually, the observation is quite obvious because I find an important muscle basically electrically silent when the other side is highly active.  This helps triangulate decisions regarding how to help the person.  I used EMG often at the USOC, particularly with broken runners and asymmetries, as a help to physicians so that they could better target what was wrong and what they might do for rehab, or in some cases – surgery.  However, I rarely used EMG alone.  I also used high-speed video (500Hz), thermal imaging, a detailed history of the athlete’s problems, and so forth.

So, don’t overreact!  EMG can be very helpful, but like an x-ray, isn’t always ideal and often combined with other measures to triangulate information to make a more informed and more confident decision.

Fred is back:

Back to my street talk. What I am reading that this talk about EMG being the end all of muscle research is all what can I say “questionable”. The problem comes into getting anyone to admit it because guess what? Then you would have to go back and question every piece of research on muscles that was done with EMG and put all kind of disclaimers in there and we all know, no one, especially in the fitness and sports industry wants to say

“I was wrong”

I had one of my friends run a search for research done with surface EMG. He gave me these to places you can see for yourself what I was talking about Medline,EMG Strength, and Google scholar, EMG Strength  Now, are all these going to go back and be redone? You can answer that.

We all know that that is unlikely to happen. If you have a comment or thought just throw them my way. Hopefully we have given you some food for thought.

Fred Koch (P-SCE), er styrketrener og bor i Kristiansand. Jeg er direktør for Tudor Bompa Institute (TBI) på verdensbasis. TBI er et internasjonalt sport- og fitness sertifiseringsprogram for personlige trenere og styrketrenere. www.fredkoch.com

E-mai Fred at ,fred@fredkoch.com

Fred Koch, P-SCE is the International Director for Tudor Bompa Institute, TBI, one of the world’s top certifications systems.

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