Reliability of flexion rotation trunk endurance test in patients with chronic non-specific low back pain

Background: Non-specific low back pain is a prevalent condition often associated with impaired core muscle function; particularly diminished endurance of trunk muscles essential for spinal stability. Effective assessment tools are vital for treatment and rehabilitation. Purpose: To evaluate the intra-rater and inter-rater reliability of the Flexion Rotation Trunk Endurance Test in assessing oblique abdominal muscle endurance in chronic non-specific low back patients and to determine the impact of pain distribution on test outcomes. Methods: This cross-sectional study involved 51 patients diagnosed with chronic non-specific low back (24 males, 27 females; aged 20–45 years). Participants underwent two sessions of the Endurance Test, separated by two days, with two trials per rater in each session. Pain intensity and functional impairment were also evaluated. Reliability analyses included Cronbach’s alpha, Intraclass Correlation Coefficients, and F-tests. Results: The Flexion Rotation Trunk Endurance demonstrated excellent intra-rater reliability (Cronbach’s alpha: 0.884 -0.906; ICCs: 0.792–0.828, p < 0.001) and inter-rater reliability (Cronbach’s alpha: 0.918–0.954; ICCs: 0.849–0.912, p < 0.001). Pain distribution was observed 45.1% bilateral, 23.5% right-sided, and 31.4% left-sided, with no significant difference (χ² = 3.647, p = 0.161). Conclusion: The Flexion Rotation Trunk Endurance Test is a reliable and practical tool for assessing core endurance in patients with chronic nonspecific low back pain, whether the pain is on the right or left side or bilateral. Its simplicity and reliability make it ideal for clinical and research use.