Differences in Psoas Major Muscle Properties Between Elite Athletes with and Without Chronic Low Back Pain

Background: Despite the proposed link between psoas major (PM) muscle dysfunction and low back pain (LBP), the relationship remains unclear. This study aimed to investigate the association between PM muscle properties, particularly stiffness, and chronic LBP in elite athletes. Methods: Ninety-nine elite athletes (age: 10 to 32 years) from gymnastics and wushu (kung fu) teams were recruited. Fifty-three had chronic LBP. PM muscle stiffness (measured by ultrasound shear wave elastography), strength, and flexibility were measured on both sides. LBP severity was assessed with the Numeric Pain Rating Scale and Oslo Sports Trauma Research Center Questionnaire on Health Problems. ANCOVA and partial correlation were conducted to analyze the association between included outcome measures and LBP, with regression analysis identifying confounding factors. Statistical significance was set at P ≤ 0.05. Results: Increased PM stiffness of the affected side was significantly associated with LBP, especially when the pain was on the dominant side (17.2% increase; mean difference [MD] = 3.21 kPa; P < 0.001) and to a lesser extent on the non-dominant side (8.7% increase; MD = 1.65 kPa; P = 0.009). Higher PM stiffness correlated with greater LBP-related dysfunction (r = 0.349, P = 0.020). No associations were found between PM strength or flexibility and LBP (all P > 0.05). Conclusion: PM muscle stiffness, but not strength or flexibility, is associated with chronic LBP and related dysfunctions. These findings highlight a potential link between PM stiffness and LBP in high-risk sports. Further longitudinal research is warranted to clarify the temporal and causal relationships.