Reliability difference between spectral and entropic measures of erector spinae muscle fatigability.

This study investigated back muscle fatigability of the erector spinae (ES) muscles during submaximal contractions with the use of surface electromyography (sEMG). It was important to confirm the reliability of measurements for characterizing neuromuscular alterations by establishing the difference between the Shannon (information) entropy and the power spectrum analysis in subjects with low back pain (LBP). The data was collected on two different days, one week apart, and the between-days reliability of these measures was examined. Thirty-two gender-matched subjects completed the modified Sorenson test; 16 of the subjects were female while 16 were male. The entropy of the sEMG signal was more reliable than either the median frequency (MF) or the slope of the MF. The intraclass correlation coefficient (ICC) was higher for the entropy than for the MF slope. The ICC values of entropy for between-day measurements were higher (0.82-0.85) than MF (0.54-0.64) and MF slope (0.26-0.30). The standard errors of measurement (SEM) values for entropy were lower (0.04-0.05) than MF (3.10-3.60) and MF slope (0.03-0.04). The Pearson correlation coefficients of the entropy were significantly higher (0.75-0.77) than those of the MF (0.38-0.47) and the MF slope (0.15-0.18). Therefore, the results of this study indicated that the entropy analysis could provide a reliable measure of muscle fatigability.