INTRODUCTION: The rising incidence of chronic nonspecific low back pain (CNLBP) is placing an ever-growing burden on healthcare systems. This study aims to investigate the multidimensional impairment characteristics of core muscle structure and function, neuromuscular control, and psychological status in patients with CNLBP and to analyze the correlations among key indicators, thereby providing a basis for individualized clinical assessment and targeted intervention. METHODS: A total of 56 CNLBP patients from the outpatient department of Rehabilitation Medicine at Xijing Hospital of Fourth Military Medical University were enrolled between June 2024 and January 2025. Additionally, 30 healthy volunteers were recruited as controls. Demographic data were collected. Assessments were conducted across four dimensions: pain and function, muscle morphology, neuromuscular control, and sleep and psychological status. Differences in indicators between groups were compared, and correlation analyses among indicators were performed within the CNLBP group. RESULTS: In the CNLBP group, the pressure pain threshold (p = 0.012), maximum voluntary extension of back extensors (p < 0.001), cross-sectional area (CSA) of the multifidus muscle (p < 0.001), thickness change rate of the multifidus muscle (p < 0.001), and flexion-relaxation ratio (FRR) (p < 0.001) were significantly lower than those in the healthy control group. In contrast, the finger-to-floor distance (p = 0.040), Pittsburgh Sleep Quality Index score (p = 0.004), Generalized Anxiety Disorder-7 score (p = 0.005), and Patient Health Questionnaire-9 score (p = 0.021) were significantly higher. Correlation analysis within the CNLBP group revealed that the FRR was negatively correlated with the NRS score (r = -0.283, p = 0.038) and the Oswestry Disability Index (ODI) score (r = -0.345, p = 0.011). The thickness change rate of the multifidus muscle was negatively correlated with the ODI score (r = -0.285, p = 0.037), but its correlation with the Numeric Rating Scale (NRS) score was not significant (r = -0.172, p = 0.214). The CSA of the multifidus muscle showed no significant correlation with the FRR (r = 0.061, p = 0.655). In contrast, a significant positive correlation was identified between the FRR and the rate of thickness change in the multifidus (r = 0.301, p = 0.024). CONCLUSION: This study confirms that CNLBP involves multidimensional impairments, including pain perception and function, multifidus muscle morphology and activation function, neuromuscular regulation of the erector spinae, and sleep quality and psychological status. The identified correlations between FRR and both NRS and ODI scores provide a crucial basis for formulating individualized rehabilitation plans and for subsequent longitudinal research. TRIAL REGISTRATION: Chinese Registry of Clinical Trials: ChiCTR2400093968.
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