REPRODUCIBILITY OF LUMBAR PARASPINAL SURFACE ELECTROMYOGRAM POWER SPECTRA

Objective. To establish the reproducibility of surface recordings of e lectromyograms from lumbar erector spinae muscles. Design. Repeated me asurements in 10 male volunteers under controlled conditions. Methods. While isometric load was held constant at 2/3 and 1/3 of maximum volu ntary contraction, surface electromyograms were recorded from the 4th/ 5th lumbar interspace on three occasions separated by at least a day. Fresh surface electrodes were applied on each test occasion. The raw e lectromyographic signal was filtered and digitized and the signal proc essed by fast Fourier transformation to give median frequency and tota l amplitude spectra. Linear regression lines of median frequency and a mplitude against time were calculated. The 'spectral halfwidth' was de fined as the full width at half maximum of the composite amplitude spe ctrum. Reproducibility was assessed by calculation of the intraclass c orrelation coefficient. Results. Reproducibility of initial median fre quency and spectral halfwidth were found to be excellent at both 2/3 ( ICCC 0.91 and 0.88) and 1/3 (ICCC 0.84 and 0.83) maximum voluntary con traction. Initial power and regression slopes of power and median freq uency were not reproducible. Conclusions. The reproducibility of two e lectromyographic variables, the initial median frequency and the spect ral halfwidth, were found to be satisfactory.