INTRODUCTION: Excessive fatigability of the low back muscles is a common finding in low back pain patients. Therefore, the assessment of the isometric endurance of these muscles has been recommended in this population. OBJECTIVE: The purpose of this study was to identify and to analyze objectively the behavior of the erector spinae muscle fatigue in an isometric endurance test performed until exhaustion. METHOD: Nine healthy subjects performed a modified Sorensen test with contractions of 5%, 10%, 15%, and 20% of the maximal voluntary contraction. The muscle fatigue was identified for the analysis of the behavior of the median frequency (MF) over time. The endurance time was inversely correlated with the contraction intensity. However, the contraction intensity did not show effect on the rate of decline of the MF. The muscle fatigue was significant in all the portions of the erector spinae muscle. RESULTS: Comparisons between the erector spinae muscles from right and left side did not show significant differences, while that the comparisons between the portions of the erector spinae muscle localized at different vertebral levels showed higher fatigue levels at L4-L5 bilaterally. CONCLUSION: Thus, the spectral analysis of the electromyographic signal was effective for the identification of the erector spinae muscle fatigue. Also, it was possible to identify functional differences between the different portions of this muscle. The knowledge of these particularities allows managing in a more specific way the prevention e rehabilitation of the low back troubles.
Spine; Electromyography; Isometric contraction; Muscle fatigue
