Improvement in multifidus muscle quality following a 12-week exercise program in patients with chronic low back pain: a randomized controlled trial

Abstract

Background: Paraspinal muscle fatty infiltration is elevated in people with chronic low back pain (LBP) compared to healthy matched controls and is associated with higher levels of disability, LBP severity and muscle dysfunction. Exercise therapy is well recognized to improve pain and disability in patients with chronic LBP, but its effect on paraspinal muscle composition remains unclear, particularly at the upper lumbar levels. We investigated the effect of a combined motor control and isolated lumbar strengthening exercise (MC+ILEX) versus general exercise (GE) on upper lumbar paraspinal muscle fatty infiltration in individuals with chronic LBP. Methods: Participants with chronic LBP were randomly allocated to each group (MC+ILEX, n = 25; GE, n = 25) and completed a 12-week supervised intervention program (2 sessions per week). IDEAL (LAVA-flex, 2-echo) fat and water magnetic resonance imaging (MRI) was acquired at baseline, 6 weeks and 12 weeks to examine the impact of each intervention on multifidus and erector spinae muscle fatty infiltration (% fat signal fraction) at L1–L2, L2–L3 and L3–L4. Results: A mixed-model analysis of variance with repeated measures revealed no significant time*group interaction for multifidus or erector spinae fatty infiltration at L1–L2, L2–L3 or L3–L4 (all p > 0.05). Both groups showed a significant decrease in multifidus fatty infiltration at L1–L2 (MC+ILEX: –4.38, 95% confidence interval [CI] –6.07 to –2.70; GE: –3.23, 95% CI –5.00 to –1.47), at L2–L3 (MC+ILEX: –3.78, 95% CI –5.52 to –2.04; GE: –2.55, 95% CI –4.30 to –0.81) and at L3–L4 (MC+ILEX: –3.71, 95% CI –5.27 to –2.14; GE: –3.07, 95% CI–4.74 to –1.39) after the intervention. A significant erector spinae fatty infiltration decrease was also observed at L1–L2 in both groups (MC+ILEX: –3.98, 95% CI –6.58 to –1.38; GE: –5.10, 95% CI –7.82 to –2.38), with no significant changes in erector spinae fatty infiltration at L2–L3 or L3–L4. Conclusion: This study provided preliminary evidence suggesting that both MC+ILEX and GE interventions included in this trial may help improve multifidus muscle quality at the upper lumbar levels in participants with chronic LBP. The effect of fatty infiltration on muscle functional capacity is understudied and warrants further investigation.