SURFACE EMG USED IN LOW BACK PAIN STUDY: REPEATABILITY OF BASELINE MEASURES.
Edward F. Owens, Jr., MS, DC, Kathryn Hoiriis, BS, DC, Bruce Pfleger, PhD
Life College, Marietta, GA
Surface EMG has been found to be a sensitive indicator of the presence of low back pain (LBP)(1). Surface EMG was found to be clinically useful when applied in a static end-range-of-motion protocol. The ratio of Thoracic to Lumbar EMG activity (T/L Asymmetry), and the presence of the Flexion-Relaxation response (FL/R) were found to be the most sensitive measures.
An EMG protocol based on the work of Leach et.al. (1) has been developed for an ongoing controlled clinical trial of Chiropractic adjustment for LBP, being carried out in the Sid E. Williams Research Center at Life College. This article is a description of the protocol being used and the results of baseline measures recorded on a series of eleven patients.
The SEMG utilized, a Precision 960 (Precision Diagnostic Technology, inc.), makes use of hand held electrodes, a 60 Hz notch filter and an 80 to 200 Hz bandwidth. Skin preparation includes vigorous mild abrasion with alcohol swabs, followed by the application of electrode cream.
The SEMG protocol involves three patient positions: neutral standing (NS), forward lumbar flexion (FF), and lumbar extension (EX). In each position, the left and right T10 sites are sampled in a 4-second window, followed by the sampling at bilateral L3 sites in the same manner. Subjects are instructed to refrain from movement during the sampling procedures, and to flex forward and backward only as far as is comfortable. The order of the positions for the test is NS, FF, EX, NS, FF, EX, NS, FF, and EX, so that the SEMG is measured at each position three times during a single examination.
Raw EMG values are recorded and stored on computer disc for data analysis. During the study each SEMG examination will be repeated six times: three during the evaluation phase for base line data (pre-adjustment), and three additional tests during the treatment phase (post-adjustment).
To date, the data for three pre-adjustment SEMG's have been collected for review on eleven patients. Of particular interest at this time are the repeatability of the measures during the same examination and stability of the measures taken on dif ferent days. Two intraclass correlations were computer for the same day trials for the trials performed on the three separate days (R=0.980 and 0.890 respectively).
The intraclass correlation coefficients suggest that EMG values remain very stable during a single testing period and fairly stable over several days. This further suggests that a single-test protocol may be sufficient in order to establish a baseline EMG.
1. Leach RA, Owens EF, Geisen JM. Correlates of Myoelectric Asymmetry detected in Low Back Pain Patients Using Hand-Held Post-Style Surface Electromyography. JMPT, 16(3) 140-149, 1993.