RELIABILITY OF ELECTROMYOGRAPHIC POWER SPECTRAL-ANALYSIS OF BACK MUSCLE ENDURANCE IN HEALTHY-SUBJECTS

Objective and Design: To investigate the reliability (within-day and b etween-days) of measurements of electromyographic (EMG) power spectral values in measurement of the fatigue rate of the back muscles. Method s: Twelve healthy male subjects were tested in the unsupported trunk h olding position for 60 seconds. Two trials were performed on each of t wo separate sessions 3 days apart. Surface recording electrodes were p laced over the iliocostalis lumborum and multifidus and a branched ele ctrode technique was used to decrease cross-talk. Outcome Measures: Me dian frequency (MF) was extracted from the EMG signals by fast Fourier transform. Initial MF and the MF slope over time were computed from l inear regression analysis. The reliability of the initial MF and the M F slope of the iliocostalis lumborum and multifidus was examined by Pe arson's product moment correlation coefficients (Pearson's r), paired t tests, and a one-way analysis of variance (ANOVA) from which intrasu bject coefficients of variation (CVintra) and intraclass correlation c oefficients (ICC) were derived. Results: For the initial MF, within-da y and between-days reliability of the iliocostalis lumborum and multif idus were good (Pearson's r = .79-.94 nonsignificant paired t test, CV intra = 6.5% to 8.5%, ICC = .79-.93). The MF slope showed moderate var iability for the iliocostalis lumborum (Pearson's r = .39-.55, nonsign ificant paired t test, CVintra = 33.0% to 48.7%, ICC = .37-.56) while better reliability was found for the multifidus (Pearson's r = .77-.87 , nonsignificant paired t test, CVintra = 25.8% to 27.5%, ICC = .78-.8 2). Conclusion: The present study indicated that the trunk holding tes t with the use of EMG power spectral analysis can be a reliable method to measure the fatigue rate of the back muscles if adequate measures are employed to minimize cross-talk. The better reliability of monitor ing the fatigue rate of the multifidus may lead to its future use as a clinical measure. (C) 1996 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilita tion