Background Exercise is a common approach for the management of patients with chronic non-specific low back pain (LBP). However, there is no clear mechanistic evidence or consensus on what type of exercise is more effective than others. While considerable evidence suggests a link between lumbar muscle health (e.g., atrophy and fatty infiltration) with functional deficits, it is unknown whether exercises targeting the lumbar spine can lead to noticeable improvements in muscle health and functional outcomes. The primary aim of this study is to compare the effect of combined motor control and isolated strengthening lumbar exercises (MC + ILEX) versus a general exercise group (GE) on multifidus muscle morphology (size and composition). Secondary aims include assessing the effect of the interventions on overall paraspinal muscle health, pain and disability, as well as psychological factors as possible effect modifiers. Methods A total of 50 participants with chronic non-specific LBP and moderate to severe disability, aged between 18 and 60, will be recruited from the local orthopaedic clinics and university community. Participants will be randomised (1:1) to either the MC + ILEX or GE group. Participants will undergo 24 individually supervised exercise sessions over a 12-week period. The primary outcome will be multifidus morphology (atrophy) and composition (fatty infiltration). Secondary outcomes will be muscle function (e.g., % thickness change during contraction), morphology, lumbar extension strength, pain intensity and disability. Potential treatment effect modifiers including maladaptive cognitions (fear of movement, catastrophizing), anxiety, depression, physical activity, and sleep quality will also be assessed. All measurements will be obtained at baseline, 6-week and 12-week; self-reported outcomes will also be collected at 24-week. Between-subjects repeated measure analysis of variance will be used to examine the changes in paraspinal muscle morphology over the different time points. Linear mixed models will be used to assess whether baseline scores can modify the response to the exercise therapy treatment. Discussion The results of this study will help clarify which of these two common interventions promote better results in terms of overall paraspinal muscle heath, back pain, disability and psychological factors in adults with chronic LBP. Trial registration NTCT04257253, registered prospectively on February 5, 2020.

Purpose The purpose of this study was to evaluate the agreement between paraspinal muscle composition measurements obtained from fat–water images using % fat-signal fraction (%FSF) in comparison to those obtained from T2-weighted magnetic resonance images (MRI) using a thresholding method. Methods A sample of 35 subjects (19 females, 16 males; 40.26 ± 11.3 years old) was selected from a cohort of patients with chronic low back pain (LBP). Axial T2-weighted and IDEAL (Lava-Flex, 2 echo sequence) fat and water MR images were obtained using a 3.0 Tesla GE scanner. Multifidus, erector spinae, and psoas major muscle composition measurements were acquired bilaterally at L4–L5 and L5–S1 using both imaging sequences and related measurement methods. All measurements were obtained by the same rater, with a minimum of 7 days between each method. Intra-class correlation coefficients (ICCs) were calculated to assess intra-rater reliability. Pearson Correlation and Bland–Altman 95% limits of agreement were used to assess the agreement between both measurement methods. Results The intra-rater reliability was excellent for all measurements with ICCs varying between 0.851 and 0.997. Strong positive correlations indicating a strong relationship between composition measurements were obtained from fat–water and T2-weighted images for bilateral multifidus and erector spinae muscles at both spinal levels and the right psoas major muscle at L4–L5, with correlation coefficient r ranging between 0.67 and 0.92. Bland–Altman plots for bilateral multifidus and erector spinae muscles at both levels revealed excellent agreement between the two methods, however, systematic differences between both methods were evident for psoas major fat measurements. Conclusion Our findings suggest that utilizing fat–water and T2-weighted MR images are comparable for quantifying multifidus and erector spinae muscle composition but not of the psoas major. While this suggests that both methods could be used interchangeably for the multifidus and erector spinae, further evaluation is required to expand and confirm our findings to other spinal levels.

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