Playing Dual Roles
The Expert Series is an on-going series of interviews with leading clinicians in the field of biofeedback lending their insights and techniques they have acquired through their many years of practice.
Gabriel E. Sella, MD, a specialist in family practice and occupational medicine, is the interviewee for the second installment of this series. Dr. Sella has lectured internationally in 15 countries on the subject of soft tissue injury, disability evaluation, sEMG, and biofeedback application in the fields of physical medicine and physiatry. He has six fellowships, three board certifications, and has conducted extensive research on the subject of the sEMG applications for the study of the range of motion. Dr. Sella has published seven textbooks, Muscles in Motion: Surface EMG Analysis of the Human Body Range of Motion; Neuro-muscular Testing with S-EMG; Muscular Dynamics: Electromyography Assessment of Energy and Motion; Graphics of Motion: The Electromyography of Muscular Dynamics; Soft Tissue Injury Evaluation: Forensic Criteria: A Practical Manual; Guidelines for Neuromuscular Re-education with S-EMG /Biofeedback; and S-EMG Muscular Assessment Reference Manual. He has several peer-reviewed publications and more than 80 international meeting presentations on subjects related to sEMG.
Q: Why is bilateral sEMG amplitude important for sEMG investigation and neuromuscular re-education (biofeedback)?
A: sEMG is the only electrophysiological modality that has a dual role and may use two parameters of activity simultaneously. Furthermore, it can be used both in the realm of objective investigation and as an objective outcome treatment measure. The amplitude parameter (microvolt RMS) is a measure of muscular activity electrical effort and to some extent of force. Bilateral measurements of homologous contra-lateral muscles are necessary in order to compare the activity of any given muscle with its counterpart. In any given condition, there should be normally a difference of <25 percent between contra-lateral muscles. A larger difference may have ergonomic or clinical value. Even if the database for most skeletal muscles activity with minimal intent will be shortly available from my work, for any given individual, the amplitude values of the asymptomatic side may represent the better control value as compared to large group values.
Most functional or myotatic units are composed generally of four or more muscles. Thus, bilateral simultaneous sEMG comparisons of four bilateral muscles may allow for a good and functional comparison. Furthermore, I have shown that it may also be indicative of the true effort or consistency of activity over several muscles. This is very important in rehabilitation medicine when it is relevant to focus on a specific muscle that needs to be re-trained. It is paramount in disability medicine when it is relevant to focus on the question of symptom magnification or malingering.
Neuromuscular re-education or sEMG biofeedback needs to have objective documentation in the present era of outcome measurement requirements. Fortunately, sEMG biofeedback can provide such documentation if the rehabilitative treatment is done according to specific and standardized type protocols. Bilateral assessment before the treatment allows for more specific functional diagnoses. The same assessment during and after the treatment period allows for an objective determination of the course of treatment and results within the clinical context of improvement and healing.
Q: Why is it important to assess and train several channels simultaneously?
A: In terms of the assessment protocols, the statistical data of coefficients of variation (CV <10 percent) will be a good determinant of the internal consistency of activity of any given muscle. In assessing simultaneously eight muscles, a CV > 10 percent (or >15 percent) will stand out as inconsistent. If it is found on a symptomatic muscle while it is not found on the seven asymptomatic muscles, it may fit within the clinical picture of abnormal. Furthermore, it will give credence to the fact that the patient or evaluee is not trying to symptom magnify since that is not quite possible to be consistent in motion on seven muscles while being inconsistent on one. The statistical parameter of correlation coefficient (c.c., p) is a good indicator of the reproducibility of any test or study. Thus, results that show good consistency will show also a c.c. > 75 percent (.75). The same reasoning of consistency described above applies. If an outlier is found and is clinically consistent with muscular symptomatology, then, sEMG can be shown to provide more objective evidence to the subjective complaints or clinical findings.
In terms of sEMG biofeedback training, the parameters above allow for the final step of the treatment outcome measurements. Obviously, the clinical results of lack of symptoms are the real outcome. However, from the point of view of objective demonstration, internal consistency of motion of CV <10 percent of the affected muscle and of c.c.>.75 of correlation of activity with the homologous contra-lateral muscle is powerful objective proof of the accuracy of the sEMG biofeedback treatment modality.
Q: What do you mean by describing your approach as clinically objective?
A: My protocols (The Sella protocols) have been described in several books, articles, and presentations. A clinician today needs objective documentation of both the diagnostic and treatment results. In terms of muscles, they can be assessed as subgroups of myotatic units, as subgroups of neuro-innervation or as bilateral homologous contra-lateral data. sEMG allows the development of protocols that corresponds with all of the above. Whether testing is done by myotatic units engaging one or more joints or by neuromuscular innervation that may affect several joints, bilateral testing can be done through the relevant range of motion (ROM) and intervening resting periods. The protocols basically stipulate the repetition times five of any given segment of ROM activity for nine seconds interspersed with nine seconds of rest intervals. The five repetitions allow for more accurate statistical data gathering and for determination of internal consistency and reproducibility along the eight muscles tested. Since the ROM is classically accepted, since the primary movers are classically known and since the neuromuscular innervation is universally accepted, the Sella protocols of sEMG testing are based on clearly accepted data.
These protocols aim for overall standardization of the sEMG procedure, like the standardization that occurred in the 1920s for the EKG procedure. I have published the database on 6,700 individual muscles tested, representing about 173 skeletal muscles investigated through 22 protocols. This database allows any clinician or investigator to compare individual findings on any given patient/evaluee with those of the database.