Background and purpose: Impaired function of trunk extensor endurance is known as a risk factor and clinical sign for low-back pain. The aim of this study was to determine the relationship between selected back muscles fatigue index and hyperlordosis. Materials and methods: This case-control study was carried out in 12 males diagnosed with hyperlordosis and 12 with normal lumbar curve. Surface electromyography activity of iliocostalis, longissimus thoracis, multifidus and gluteus maximus muscles were recorded during performing Sorensen test until exhaustion. Independent t-test and Pearson correlation coefficient were used for data analyses (P<0.05). Results: Median frequency slope decreased significantly for iliocostalis lumborum (P=0.022) and multifidus (P=0.004) muscles. Gluteus maximus muscle had a high correlation with endurance time among hyperlordotic group (r=0.87, P=0.005). Conclusion: Lower median frequency in the iliocostalis lumborum muscle in hyperlordosis group resulted in reduction of median frequency in the multifidus muscle. According to our findings, the gluteus maximus and the iliocostalis lumborum muscles were important determinant of endurance time in case and control groups, respectively. Therefore, iliocostalis lumborum and multifidus muscles training program should be considered in individuals with increased lumbar lordosis while Gluteus maximus training is beneficial for subjects with normal lumbar curve.

Keywords: Back muscles endurance, median frequency, Sorensen test, electromyography

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