Comparison of psoas major activation during standing hip flexion between chronic low back pain and healthy populations.

Background: The psoas major (PM) has been identified as a potential contributor to chronic low back pain (LBP). However, few studies have investigated the effects of upright functional movement on PM activation in cLBP individuals.

Objective: This cross-sectional study aims to compare PM muscle activation characteristics in chronic LBP (cLBP) and healthy subjects during the transition from quiet double-leg standing to standing hip flexion.

Methods: Ultrasound Imaging was used to assess PM thickness at the lumbar vertebral level of L4-5 in 12 healthy and 12 cLBP participants. The changes in thickness between the test positions were utilized as a proxy for PM activation.

Results: The cLBP group exhibited greater thickness changes on the non-dominant side PM during contralateral hip flexion but not ipsilateral hip flexion (p= 0.369) compared to their healthy counterparts (p= 0.011; cLBP: resting 27.85 mm, activated 34.63 mm; healthy: resting 29.51 mm, activated 29.00 mm). There were no significant differences in dominant side PM thickness changes between the two groups during either contralateral or ipsilateral hip flexion (p= 0.306 and p= 0.077).

Conclusion: Our findings suggest a potential overactivation of the PM in the cLBP population. This insight may aid in the development of tailored rehabilitation programs.