Abstract Background Non-specific chronic low back pain (NSCLBP) is a prevalent clinical condition often associated with impairments of the lumbar motor control (LMC). A test battery of 13 tests has been developed to evaluate LMC. However, the flexion-specific items demonstrated low item difficulties, limiting their diagnostic utility. Consequently, four new items for flexion were included and assessed for inter-rater reliability. The aim of this study was to evaluate and compare the item difficulty of both the original and newly proposed flexion-related LMC tests. Methods This cross-sectional observational study included 69 participants (45 with NSCLBP, 24 without). Mean age was 50.5 years (SD 16.8) in the NSCLBP group and 45.9 years (SD 20.4) in the control group; the proportion of females was 73% (NSCLBP) and 62.5% (controls). Each participant completed eight flexion-specific LMC test items, rated as correct or incorrect by a blinded physiotherapist. In addition, participants completed questionnaires collecting demographic data and NSCLBP-specific information. Descriptive statistics were calculated, and group comparisons were performed with t-tests or Mann–Whitney U tests (significance level p < 0.05). Item Response Theory (IRT) analyses employing a one-parameter logistic model (1-PL) were carried out to estimate item difficulty. The test characteristic curve (TCC) and test information function (TIF) were computed for the full test battery. Results Item difficulty of the flexion-specific items ranged from − 3.15 (easiest: forward bend) to -0.17 (most difficult: box lift). Two of the four new items exhibited higher difficulty than the existing tests. Participants with NSCLBP performed fewer flexion-specific tests correctly (mean: 5 out of 7) compared to those without NSCLBP (mean: 6 out of 7). The test battery was most informative for individuals with average to below-average LMC ability (θ range: 0 to -2.9). Conclusion Although the newly introduced flexion items showed slightly higher difficulty, they remain insufficiently challenging to discriminate LMC deficits in individuals with mild impairments. Future research should focus on developing flexion-specific LMC tests with greater difficulty levels to improve clinical discrimination in athletic people. Trial registration At OSF: https://doi.org/10.17605/OSF.IO/GR2WZ .
Hoffmann et al. (Thu,) studied this question.