Charlie or anybody else that knows this stuff, I have a couple of questions regarding your “truth about EMS” article on T-mag (issue 159).
Firstly I don’t understand why the cybex studies comparing max voluntary torque to that achieved by EMS are flawed… does your criticisim include isometric measures in a cybex?
And secondly what is a tensiometric device? How does it measure muscle tension, is it invasive?
Thanks
[QUOTE=rossa]Charlie or anybody else that knows this stuff, I have a couple of questions regarding your “truth about EMS” article on T-mag (issue 159).
Firstly I don’t understand why the cybex studies comparing max voluntary torque to that achieved by EMS are flawed… does your criticisim include isometric measures in a cybex?
And secondly what is a tensiometric device? How does it measure muscle tension, is it invasive?
The tests with Cybex simply hooked subjects up to a cybex machine and measured how much force was generated to move the lever when EMS was used on the quad muscles. This doesn’t consider the way these muscles work over two joints (same for the hamstrings)- but does point out the level of smarts of the researchers involved.
The Russians used devices to measure the tension within the muscle as a measurement tool. (Interesting, but not really needed, because you can use your own senses by doing a maximal isometric contraction on a muscle group- and then adding EMS, so you can feel how it superceeds your own maximum voluntary output capacity, if you crank it up enough!).
Thanks for your reply Charlie, a couple of thoughts… I accept that one of the quads is bi-articular (Rectus Femoris) in that it acts over both the hip and knee joints. However if a subject is strapped down at the hip and knee extension force is being assessed on a cybex, surely the shortening of rec fem causes both attempted hip flexion (isometric if hip/trunk is stabilised) and knee extension and that the force (in conjunction with the force from the other 3 quads which are pure knee extensors) should be measurable via the Cybex? I don’t understand what you mean with regard to this being different to a voluntary contraction either, doesn’t a voluntary cybex knee extension also rely on all 4 of the quads for force production as well, and although knee extn is not the primary function of RF it would have a limited role here…. Am probably being slow but still not clear on the discrepancy as you have described it.
Intuitively I agree with you to some extent however, as in my limited experience with EMS the muscle tension does appear in excess of that produced by voluntary contractions even when the recorded torque is less. Could it be that the torque produced via EMS is less because not all motor units are activated with the surface stimulation and although the tension may be greater (than can be achieved in an MVC) in accessible surface motor units, it may be below maximal in the deeper less accessible motor units? Also interesting to note that some studies with very high levels of electrical stimulation, knee extension torque on a cybex is higher than MVC (eg Delitto et al., 1989 reported up to 126% of MVC). Perhaps the greater current used allows more complete activation of the whole muscle group (quads)? Be interested in your thoughts…
Maybe we are on the same page and you are suggesting that Rec fem in a seated position is already shortened and is a relatively poor knee extensor anyway. This combined with RF being probably the most easily activated of the quads with EMS (+ its muscle tension is not well registered with knee extn torque) and if the other quads are below max, EMS knee extn force will remain below MVC?
It is possible to “Flood” the muscle group with current, as the current spills over from the fibre already under contraction to underlying fibre if there’s enough juice. Also, muscles do work through a coordinated, organized contraction, rather than via a simultaneous contraction of all available fibres, even though strength is enhanced via both means.