Reliability and validity of trunk strength and endurance tests in athletes with low back pain

Background Low back pain (LBP) is a common problem in athletes including those in Gaelic games. Valid, reliable and feasible clinical tests to evaluate trunk function are necessary for practitioners working in the field. Objectives This pilot study aimed to investigate the intra-rater reliability and known-groups validity of tests for isometric trunk muscle strength using a hand-held dynamometer (HHD) and trunk endurance using the McGill protocol and novel ‘long-lever’ tests in a group of male Gaelic games athletes, with and without LBP. Methods Nine participants with and without LBP were recruited. All completed a battery of strength and endurance tests. Intra-tester (relative and absolute) was determined by calculating the intraclass coefficients (ICC 2,1), standard error of measurement and minimal detectible change. Known-groups validity was investigated using independent T-tests and measuring the effect sizes (Cohen’s d ) of the tests. Results Isometric strength testing using an HHD for flexion, extension and rotation showed excellent reliability for both groups (ICC = 0.78–0.89). All endurance tests, except the long-lever lateral flexion tests, showed excellent intra-tester reliability in both groups (ICC = 0.76–0.98). Three tests, right isometric lateral flexion strength, isometric extension strength and the Biering-Sorensen endurance test, were shown to discriminate between those with and without LBP in this cohort ( p < 0.05). Conclusion Isometric strength testing using an HHD and certain endurance tests are reliable, valid and feasible for use in athletes with and without LBP. Isometric extension strength and endurance can discriminate between those with and without LBP.