Habitual Cross-legged Sitting Increases Lumbopelvic Rotation Asymmetry

Background: Cross-legged sitting posture (CLSP) is common in daily life but may cause asymmetrical loading of the pelvis and spine, potentially leading to postural imbalance and musculoskeletal problems. Although short-term effects of CLSP have been reported, the longterm biomechanical consequences of habitual CLSP remain unclear. Objects: This study compared lumbopelvic alignment and rotational asymmetry between individuals with and without habitual CLSP. Methods: Thirty healthy adults were classified into CLSP (n = 15) and non-CLSP (NCLSP; n = 15) groups based on self-reported sitting habits. Transverse plane pelvic rotation angle (TrPRA) in the supine position and during active straight leg raise (ASLR) was measured using a Smart KEMA motion sensor system, and side-lying lumbopelvic rotation range of motion (SLRR) was assessed with a custom device. Asymmetry index (AI) was calculated for left–right differences. Group comparisons were analyzed using independent t-tests (p < 0.05). Results: Intra-rater reliability of SLRR was very high (intraclass correlation coefficient = 0.958–0.986). No significant group differences were found in TrPRA in the supine position (p > 0.05) or AI of TrPRA during ASLR (p > 0.05). However, the CLSP group demonstrated significantly greater AI in SLRR than the NCLSP group (13.21% ± 6.64% vs. 7.06% ± 4.90%, p = 0.008, Cohen’s d = 1.05). In 10 of the 15 CLSP subjects, the direction of lumbopelvic rotation corresponded to the preferred leg-crossing side. Conclusion: Habitual unilateral CLSP is associated with significantly greater lumbopelvic rotational asymmetry during active side-lying movement, which may contribute to functional imbalance and increased injury risk. Preventive and corrective strategies should include limiting prolonged CLSP, adopting ergonomic seating, and implementing bilateral mobility, rotational control, and core stability exercises. Postural retraining with visual feedback and task-specific practice may further promote symmetrical sitting habits in clinical and occupational environments.