Improving the Reproducibility of the Standing Forward Flexion Test After Specific Training: A Cross-Sectional Study

The standing forward flexion test (SFT) is commonly used in osteopathic and manual therapy practice to assess sacroiliac joint mobility, yet its reliability has long been questioned due to inconsistent inter- and intra-examiner agreement. This cross-sectional study evaluated whether a structured palpatory training program could improve the reproducibility of the SFT and analyzed which phase of the test-trunk flexion or standing contributes most to variability. Two senior osteopathy students independently assessed the posterior superior iliac spines (PSIS) of 72 asymptomatic participants across three sessions: baseline (T0), after 25 hours of specific training (T1), and final assessment (T2). In addition to the classical SFT, separate measurements were performed for each phase, allowing phase-specific comparison and the development of a "reverse SFT" procedure, in which palpation is executed first in flexion and then in standing. Agreement was quantified using weighted Cohen's κ, Gwet's AC2, and Brennan-Prediger κ. At baseline, reliability was poor (κw ≈ 0.14), consistent with previous literature. After training, both intra- and inter-examiner reproducibility increased substantially (κw = 0.60-0.83; AC2 = 0.60-0.82; Po = 0.81-0.92), with slightly higher agreement in flexion than in standing. These results demonstrate that palpatory variability is not an intrinsic limitation of manual assessment but reflects insufficient training and methodological inconsistency. A structured 25-hour consensus-based program can markedly improve diagnostic reproducibility, and the reverse SFT may represent a more stable and standardized approach for both educational and clinical use.