Surface deception - surface EMG

Although the article that stimulated this blog was published in February, I was only alerted to it by an automated Google news search, whose results that were emailed to me this week. The article is about the use of surface EMG to diagnose chiropractic subluxations. I won't go into the validity of the concept of the subluxation as I have co-authored a paper on that already, and the literature that supports or refutes our paper has not changed in any substantive way that I know of.

The article, sEMG: An overview, in my opinion, does little more than express, what I think, is a biased belief lacking any evidence that a subluxation can be demonstrated by sEMG. sEMG or surface EMG is a useful tool for certain purposes. One of those purposes doesn't happen to be diagnosis. It is really a research tool. Used to determine which muscle is active during certain movements. There are some sophisticated methods that are showing some promise in determining dysfunction that may be at the root of low back pain (1) or validating the diagnosis of low back pain. (2) but nothing I have seen suggesting that the sEMG can help find a subluxation. (3)

One fundamental problem with the use of sEMG to diagnose subluxations is that none of the methods used by my colleagues at this time involve what is called normalization. Normalization is where one converts the electricity measured during the sEMG to percent of maximum volitional movement or percent of some predetermined activity. The reason normalization is important is if one is just trying to compare the voltage from one patient to set of "normal" values inside the device one does not account for variables that change that voltage independent of muscle activity. For example, if one has an obese patient and thin one, the obese patient will have lower voltage readings on the EMG because fat is a great insulator without regard to the actual activity of the muscle. (4, 5) None of the sEMG devices that are marketed to chiropractors require normalization procedures before they produce their pretty computer graphics supposedly showing where the subluxation is.

Now most doctors of any profession lack the training that would provide them with the knowledge to evaluate the claims of the sEMG manufactures. However, if one reads the sEMG: An overview there are to simple clues to the lack of validity of these devices. The only references used are a twenty-two year old pilot study and a twenty year old book. Given the fact that approximately ten thousand papers are published weekly in the biomedical literature it is not that common that one needs to rely on such old references. Especially when professional groups both outside (6) and inside the chiropractic profession (7) have published since then noting the lack of validity of the use of these devices.(6, 7)

SMP

1. Cholewicki J, Silfies SP, Shah RA, Greene HS, Reeves NP, Alvi K, et al. Delayed trunk muscle reflex responses increase the risk of low back injuries. Spine. 2005 Dec 1;30(23):2614-20.
2. Geisser ME, Ranavaya M, Haig AJ, Roth RS, Zucker R, Ambroz C, et al. A meta-analytic review of surface electromyography among persons with low back pain and normal, healthy controls. J Pain. 2005 Nov;6(11):711-26.
3. Owens EF, Jr. Chiropractic subluxation assessment: what the research tells us. J Can Chiropr Assn. 2002;46(2):215-20.
   
4. Lehman GJ, McGill SM. The importance of normalization in the interpretation of surface electromyography: a proof of principle. J Manipulative Physiol Ther. 1999;22(7):444-6.
5. Ng JK, Kippers V, Parnianpour M, Richardson CA. EMG activity normalization for trunk muscles in subjects with and without back pain. Med Sci Sports Exerc. 2002 Jul;34(7):1082-6.
6. Pullman SL, Goodin DS, Marquinez AI, Tabbal S, Rubin M. Clinical utility of surface EMG: report of the therapeutics and technology assessment subcommittee of the American Academy of Neurology. Neurology. 2000 Jul 25;55(2):171-7.
7. Position Statement of the American College of Chiropractic Consultants on sEMG 2006