Morphological and Compositional Features of Lumbar Multifidus in Athletes with Chronic Non-specific Low Back Pain: A Systematic Review and Meta-Analysis.

Background: Chronic non-specific low back pain (CNSLBP) is highly prevalent in athletes, causing significant time loss up to one year. In the general population, CNSLBP is associated with morphological and compositional changes in lumbar multifidi, a key spinal stabilizer group, including reduced cross-sectional area (CSA), muscle thickness (MT) and increased echo intensity (EI). Whether these differences exist in athletic population is unclear. Hypothesis/Purpose: This systematic review and meta-analysis examined the morphology and composition of the lumbar multifidi at two levels in athletes with and without CNSLBP. Study design: Systematic review with meta-analysis. Methods: Following PRISMA guidelines, four databases (PubMed, CINAHL, Embase, and Web of Science) were searched from inception to May 2025 using a brief string of search terms (e.g., "athletes" OR "sports" AND "low back pain" AND "multifidus" OR "paraspinal muscles", see Supplementary Table 1 for the full search strategy) for studies comparing lumbar multifidus features in athletes with and without CNSLBP. Studies were included if they: (i) compared athletes with CNSLBP (pain >3 months) to asymptomatic athletes; (ii) measured CSA, MT, or EI of the lumbar multifidus; and (iii) were observational or interventional studies. Exclusion criteria were non‑athletic populations, specific spinal pathologies (e.g., radiculopathy, infection, tumor), and non‑original articles (reviews, case reports, editorials). Study quality was assessed using the Newcastle-Ottawa Scale (NOS) and Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. Data were pooled using a random-effects model. Results: From 850 records, 18 studies (n=1142 subjects) were included. NOS and GRADE assessments revealed poor methodological quality of the included studies on lumbar multifidus assessments. Meta-analysis revealed no statistically significant differences between athletes with and without CNSLBP in CSA at L4/L5 (MD = -0.21; p = 0.34) or L5/S1 (MD = -0.25; p = 0.19), MT at L5/S1 at rest (MD = -0.05; p = 0.62) or contracted (MD = -0.05; p = 0.47), or EI at L5/S1 (MD = 2.24; p = 0.07). Conclusion: This review found no significant differences in morphology and composition of lumbar multifidus between athletic groups. Findings were constrained by heterogeneous methodologies, imprecise reporting, and suboptimal study quality. Despite these limitations, ultrasound technology remains a promising tool for soft tissue assessment in athletes. Level of Evidence: 2 (Systematic review of observational studies).