Between-Week Test-Retest Reliability of Some Endurance Measures in the Trunk Extensors

Abstract

Back muscle endurance, fatigability and perception of fatigue can be measured by Sorensen test time, two electromyographic (EMG) median frequency (MF) parameters, the initial median frequency (IMF) and MF slope, and the Borg's rating scale of perceived exertion. The purpose of this study was to examine the between-week, test-retest reliability of these parameters in healthy individuals. Sixteen male and 16 female adult volunteers without current back pain consented to the study. The subject performed the Sorensen test that was to maintain the upper trunk unsupported in a horizontal position. The test ended and the endurance time (TIME) was recorded when the subject was no longer able to hold the position. The EMG signals of the right and left erector spinae muscles from the 5th to the 35th second into contraction were recorded by surface EMG. The IMF's and MF slopes were obtained by Fast Fourier Transformation and linear regression analyses of the EMG signals from each recording site. Data from the right and left sides were averaged. Each subject self-rated the level of fatigue in the back muscles at the 35th second into the test according to the Borg's 10-point scale for perceived exertion (RPE). Each subject repeated the test in two weeks. Repeated measures multivariate analyses of variance showed the IMF and MF slope of the two sides were not significantly different. The between-week, test-retest reliability, as determined by the intraclass correlation coefficient ICC(2,1) model, was good to excellent for TIME (.95) and RPE (.82), acceptable for the IMF of the right and left erector spinae muscles (.72 and .75), but poor for the MF slope of the two muscles (.46 and .67). The Sorensen test and the RPE were reliable measures of endurance and perception of fatigue of the back muscles. The IMF of the erector spinae muscles had acceptable test-retest reliability over two weeks. However, the MF slope of the erector spinae muscles was not a reliable measure over weeks unless an averaged value could be used.