Low back pain during prolonged sitting on a sofa is associated with pelvic posterior tilt in individuals with non-specific chronic low back pain

PURPOSE: Nonspecific chronic low back pain (NSCLBP) is a prevalent musculoskeletal disorder often aggravated by prolonged sitting. Previous studies have linked trunk muscle activity and posture to pain development, but their findings were inconsistent. Furthermore, previous studies did not use a backrest, so the study conditions did not reflect real-life conditions. The present study investigated the relationship between pain intensity, pelvic and trunk alignment, and lumbar muscle activity during sofa sitting in individuals with and without NSCLBP. METHODS: Eighteen participants with NSCLBP and 19 healthy controls sat on a standard sofa for 30 min. Pelvic and trunk angles were measured using a markerless motion capture system, and lumbar longissimus and multifidus muscle activity was recorded via surface electromyography. Pain intensity was assessed using a numerical rating scale. RESULTS: Both groups showed significant posterior pelvic tilt and trunk extend after 30 min (Pelvis: mean difference [MD]: -1.64°, 95% CI: -2.64 to -0.64; P = 0.002, Trunk: MD: -3.70°, 95% CI: -6.02 to -1.37; P = 0.003). Numerical rating scale (NRS) scores increased significantly over time (MD: 1.62, 95% CI: 1.13 to 2.12; P < 0.001). No significant changes were observed in lumbar muscle activity and trunk flexion angle relative to the pelvis. In the NSCLBP group, worsening pain correlated with increased posterior pelvic tilt (r = - 0.694, P = 0.001). CONCLUSION: Prolonged sofa sitting exacerbates low back pain in patients with NSCLBP, primarily associated with posterior pelvic tilt rather than lumbar muscle activity. Postural guidance encouraging anterior pelvic tilt may help reduce pain during prolonged sitting in daily life.