Background and Objective: Previous studies demonstrated that the prevalence of lumbar disc herniation (LDH) is relatively high. This investigation aimed to evaluate the size of lumbar multifidus (LM) muscle in patients with different degrees of LDH compared to healthy group, during rest and contraction, using ultrasonography. Materials and Methods: In this non-experimental, analytic, and case control study, ultrasound imaging was used to assess cross-sectional area (CSA) and thickness of the LM muscle in 15 healthy subjects and 60 patients with different stages of LDH (bulging group = 15, protrusion group = 15, extrusion group = 15, sequestration group = 15). Measurements were taken bilaterally at the L4–L5 level, during rest and contraction and results were compared between groups. Results: There was a significant difference between healthy subjects and the extrusion and sequestration groups during rest and contraction for LM muscle CSA and thickness (p = 0.001), as LM muscle CSA and thickness were significantly smaller in extrusion and sequestration patient groups compared to healthy subjects. LM atrophy was greater in patients with extrusion and sequestration groups than in patients with bulging and protrusion, both at rest and during contraction. Significant correlations were also observed between functional disability and intensity of pain with LM CSA and thickness measurements. Conclusions: Patients with extrusion and sequestration LDH had smaller LM muscle at rest and during contraction compared to healthy subjects. Larger LDH lesions were associated with decreased LM muscle size. Patient with more pain, disability, and extrusion and sequestration LDH had greater LM size changes. LM muscle size was not correlated with symptom duration. Further investigation with greater sample size is warranted.

Low back pain (LBP), a globally widespread and persistent musculoskeletal disorder, benefits from exercise therapy. However, it remains unclear which type leads to greater changes in paraspinal muscle health. This study aimed to (1) compare the effects of a combined motor control and isolated lumbar extension exercise (MC+ILEX) versus a general exercise (GE) intervention on paraspinal muscle morphology, composition, and function, and (2) examine whether alterations in paraspinal muscle health were correlated with improvements in pain, function, and quality of life. Fifty participants with chronic LBP were randomly assigned to each group and underwent a 12-week supervised intervention program. Magnetic resonance imaging and ultrasound assessments were acquired at baseline, 6 and 12 weeks to examine the impact of each intervention on erector spinae (ES) and multifidus (MF) muscle size (cross-sectional area, CSA), composition, and function at L4-L5 and L5-S1. Self-reported questionnaires were also acquired to assess participant-oriented outcomes. Our findings indicated that the MC+ILEX group demonstrated greater improvements in MF and ES CSA, along with MF thickness at both levels (all p < 0.01). Both groups significantly improved in pain, function, and quality of life. This study provided preliminary results suggesting that an MC+ILEX intervention may improve paraspinal morphology while decreasing pain and disability.

Purposes: While lumbar multifidus (MF) muscle alterations are linked to low back pain (LBP), the structure-function relationship is not fully understood. This study aims to evaluate the relationship between fatty degeneration of the lumbar MF muscle and its function in individuals with and without LBP. Methods: The study included 25 participants with chronic nonspecific LBP and 25 age- and sex-matched healthy controls. Participants underwent MRI assessment for MF fat infiltration, utilizing IDEAL fat-water images. Ultrasound measures evaluated MF function, including shear-wave elastography (SWE) for stiffness/elasticity and thickness ratio from rest to submaximal contraction. All measurements were acquired at L4/L5 and L5/S1 spinal levels, bilaterally. Bivariate and multivariable linear regression models were used to assess the relationship between morphology and function, while age, sex, body max index (BMI), physical activity levels, and LBP status were considered as covariates. Results: Fifty participants (26 females) were included (mean age: 39.22 ± 11.67). Greater % MF fat at L4/L5 was significantly associated with greater MF SWE ratio (p = 0.002). No significant bivariate or multivariable relationships were found between MF fat infiltration and MF thickness ratio. Participants with LBP exhibited lower contraction ratios (p = 0.017) and higher SWE during contraction (p = 0.03) at L4/L5 compared to controls. Conclusion: This study highlights a positive association between MF fat infiltration and SWE-based stiffness measures at L4/L5, suggesting altered muscle composition may impacts MF function. However, no relationship was found between MF fat infiltration and contraction. Participants with LBP demonstrated distinct deficits in muscle activation, supporting the need for targeted rehabilitation strategies addressing these functional impairments.

Purpose The purpose of this study was to investigate the relationship between different characteristics of the Thoracolumbar Fascia (TLF) (e.g., length, epimuscular fat distribution) with pain status and lumbar extension strength in a sample of participants with and without chronic low back pain (CLBP). Methodology This cross-sectional study included 27 individuals with CLBP (10 males, 17 females; mean age 41.45 ± 11.21 year) and 25 healthy controls (12 males, 13 females; mean age 36.56 ± 11.43 year). The length of the posterior (pTLF), middle (mTLF), and anterior (aTLF) TLF layers, the TLF circumference, and the distribution of epimuscular fat around the paraspinal muscles were assessed at L4 and L5 using MRI. Pain severity was collected using a visual analogue scale (VAS), and lumbar extension strength was measured using the MedX lumbar extension machine. ANCOVA testing and multiple regression models were used to assess possible differences in TLF characteristics between participants with and without CLBP, and partial correlations were used to assess the relationship between TLF characteristics and extension strength. Results We found no significant differences in TLF morphological characteristics between participants with and without CLBP. None of the TLF characteristics or epimuscular fat characteristics investigated were correlated with pain severity. Participants with CLBP showed no correlation between pTLF length and strength (r_avg = 0.276, r_max = 0.421, p > 0.05) contrary to healthy controls (r_avg = 0.527, r_max = 0.554, p < 0.05). The TLF circumference (r_maxL4 = 0.495 r_maxL5 = 0.571, p < 0.05) and fat surface of contact (r_avgL4 = 0.709, r_maxL4 = 0.596, p < 0.05) in CLBP participants were significantly correlated with back extension strength, contrary to healthy controls. Conclusion Future studies investigating TLF characteristics at multiple spinal levels while also considering the multidirectional and multilayered implications of the TLF are needed to better clarify the role of TLF morphology in spine biomechanics.