Ok I wanted to discuss the series of articles on T-nation that Bret Contreras has been writing. He has been using EMG done on only himself to make specific recommendations on what the best exercises are for body parts. I have been sceptical of his conclusions and the most recent article tipped me over the edge.
I was thoroughly amazed at his conclusions, but even more so in his measurements. Upper, mid and lower pecs?? (I noted that one exercise already known to decrease clavicular head involvement had a "mid chest" value exactly between the "upper" and "lower" values) I take issue with the publication of this sort of article, as it lacks real data and is very misleading.
Of course you can't debate the article on the forums there
Here is an article that covers some points on EMG:
http://markyoungtrainingsystems.com/...commendations/QuoteWhen I was back in university I have to admit that I was a little bit of a biomechanics geek. These days I like to think I’m just more of your normal all around kind of geek, but I digress.
Having spent a lot of time in a biomechanics lab I had the opportunity to do my fair share of EMG analysis. And although it has been quite some time since I’ve done any hands on EMG work, I’d still consider myself versed enough to share a little bit about it.
But why are you going to bore us to tears with all this EMG crap?
Because I think that recently there has been a lot of talk about EMG for the determination of optimal training movements and I don’t think the general training public completely understands this enough to make a decision about whether this is valuable or not. Instead, I think most people just believe that you slap on the electrodes, contract, and look at which muscles were most active.
Here’s a typical rundown on how EMG testing is really done in a biomechanics lab.
- - EMG electrodes are placed on or in the muscle belly of the muscle group to be recorded. Note that you can use either surface electrodes that just stick on the skin or fine wire electrodes that actually stick right into the muscle.
- - The segment to be examined (leg, arm, etc) is strapped into a jig of some kind to allow the researcher to measure the torque created when the muscle contracts.
- - The muscle is contracted through a certain range of motion or for a certain amount of time and the EMG and torque are recorded.
- - Since the EMG signal is recorded in millivolts it needs to be amplified before it is recorded.
- - At this point, the raw EMG signal is atually quite messy looking and if you were to try and make any conclusions from this you’d be completely out to lunch.
- - To make the EMG more usable it needs to be full wave rectified which basically means taking the absolute value of the signal. This will put the whole signal on the positive side of the line.
- - Then the signal needs to be filtered to take out all noise that might be impeding you from seeing the actual signal you’re trying to get at. A filter is often used to filter out electrical noise (introduced by the electrical equipment), electromagnetic radiation, and motion artifact(often introduced by swaying wires as the limb moves during the trial).
- - Once you’ve gotten this far you SHOULD have a relatively clean EMG signal, but you’re still not done. In many cases people will average or integrate the EMG to get a clearer picture of muscle effort.
In the picture below you can see the progression from the raw EMG, to full wave rectified, to filtered, and then integrated.
This signal can then be compared to the torque measured from the limb to establish a relationship between the amount of muscle activity and the amount of force that can be generated.
So more EMG activity is equal to more muscle force?
Not exactly. And this is where the problem lies. Unfortunately the relationship between muscle force and EMG is not linear. In other words, when EMG goes up, muscle force does not necessarily increase at the same rate. One does not clearly relate to the other.
Why does this happen?
There are a few things about EMG that make it tricky (even for the best researchers).
1. Crosstalk between muscles often occurs when an electrode covers an area where several muscles are located. For example, electrodes placed over the bicep will record bicep activity, but they can also pick up the signal of the brachialis which is deep to the bicep. Fine wire electrodes that go directly into the muscle can decrease this, but many studies opt not to use these.
2. EMG best predicts muscle forces during isometric contractions. Of course, when it comes to exercise, we want to look at movement so this creates problems. When the arm moves, the muscle can move beneath the electrodes which means that different parts of the muscle are being picked up for the EMG signal. This can make the prediction of muscle forces difficult.
3. The real truth is that when you’re measuring the force of the bicep curl, you’re not really measuring the force of the bicep muscle itself. You’re actually measuring something called torque which is a product of the force of the bicep muscle and its moment arm with the force at the hand and its moment arm.
In non-geek terms, it means you have to calculate the muscle force of the bicep because you can’t really measure it directly unless you were to attach some sort of transducer to the muscle itself. (I should note that a researcher named Paavo Komi used to do this buy surgically implanting a buckle transducer on his achilles tendon). Sadly, since other muscles cross the elbow and contribute to flexion, the calculation of muscle force is damn near impossible without an elaborate computer program. If you’ve ever seen the math behind Dr. Stuart McGill’s muscle force predicting model you know how crazy this can get.
But what if we had such a program, could we compare the EMG to other exercises?
You sure could, but again, you need to remember that when you’re comparing different dynamic exercises that are near maximally loaded with surface electrodes you’ve already introduced all sorts of potential error. If you did want to do it though, you’d need some way to standardize the results.
What researchers typically do is have the person do a maximal voluntary contraction and compare all EMG results to this. For example, if you were doing two different bicep exercises you might say that the dumbbell bicep curl yielded 90% MVC whereas a pronated curl produced 65% MVC or something of the sort.
Not doing this can actually lead to erroneous results. One such case was when it was reported that certain exercises hit the upper abdminals and others hit the lower abdominals to a greater degree. However, after the signals were presented as a percent of MVC the differences disappeared. In other words, this demonstrated that you cannot differentially train the upper and lower abs.
I guess my main point here is that while EMG is an incredibly useful tool in the hands of some researchers, it can lead to terrible confusion and inappropriate recommendations in the hands of others.
Always be open minded, but maintain some degree of healthy skepticism of whatever you read…except my blog…which is perfect. :)
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