Reliability and concurrent validity of the bubble inclinometer for visual estimation of straight leg raise in asymptomatic individuals

Introduction The straight leg raise (SLR) test is commonly used to investigate neurodynamic problems or hamstring muscle length. Visual estimation can be used to identify the degrees of hip flexion during the SLR test. However, intra-tester and inter-tester reliability, as well as concurrent validity, await formal investigation. Methods This study was an experimental study. Two testers, a novice and an experienced physical therapist, measured hip flexion angles during the SLR test using visual estimation for two sessions and the bubble inclinometer method during the first session in 31 asymptomatic participants, in random order. Intra-tester reliability (intraclass correlation coefficient, ICC<sub>3,3</sub>), inter-tester reliability (ICC<sub>2,3</sub>), concurrent validity (Pearson correlation with bubble inclinometer), and measurement error was represented as standard error of measurement (SEM) and minimal detectable change (MDC), were calculated. Results The concurrent validity and intra-tester reliability of visual estimation for both testers were good (ICC<sub>3,3</sub> = 0.885 with 95% confidence interval = 0.775–0.943, <i>p</i> < 0.001) and excellent (ICC<sub>3,3</sub> = 0.904 with 95% confidence interval = 0.810–0.952, <i>p</i> < 0.001), respectively. Inter-tester reliability of visual estimation was poor (ICC<sub>2,3</sub> = 0.373 with 95% confidence interval = 0.027–0.639, <i>p</i> = 0.018). Conclusions Although the concurrent validity of visual estimation with the bubble inclinometer was good, and intra-tester reliability was excellent, the inter-tester reliability was poor. Therefore, caution should be exercised if more than one tester is involved in visual estimation.