Does Change in Isolated Lumbar Extensor Muscle Function Correlate with Good Clinical Outcome? A Secondary Analysis of Data on Change in Isolated Lumbar Extension Strength, Pain and Disability in Chronic Low Back Pain

Purpose: Secondary analysis of data from studies utilising isolated lumbar extension exercise interventions for correlations among changes in isolated lumbar extension strength, pain, and disability. Materials and methods: Studies reporting isolated lumbar extension strength changes were examined for inclusion criteria including: (1) participants with chronic low back pain, (2) intervention ≥ four weeks including isolated lumbar extension exercise, (3) outcome measures including isolated lumbar extension strength, pain (Visual Analogue Scale), and disability (Oswestry Disability Index). Six studies encompassing 281 participants were included. Correlations among change in isolated lumbar extension strength, pain, and disability. Participants were grouped as “met” or “not met” based on minimal clinically important changes and between groups comparisons conducted. Results: Isolated lumbar extension strength and Visual Analogue Scale pooled analysis showed significant weak to moderate correlations (r = −0.391 to −0.539, all p < 0.001). Isolated lumbar extension strength and Oswestry Disability Index pooled analysis showed significant weak correlations (r = −0.349 to −0.470, all p < 0.001). For pain and disability, isolated lumbar extension strength changes were greater for those “met” compared with those “not met” (p < 0.001–0.008). Conclusions: Improvements in isolated lumbar extension strength may be related to positive and meaningful clinical outcomes. As many other performance outcomes and clinical outcomes are not related, isolated lumbar extension strength change may be a mechanism of action affecting symptom improvement. Implications for Rehabilitation: Chronic low back pain is often associated with deconditioning of the lumbar extensor musculature. Isolated lumbar extension exercise has been shown to condition this musculature and also reduce pain and disability. This study shows significant correlations between increases in isolated lumbar extension strength and reductions in pain and disability. Strengthening of the lumbar extensor musculature could be considered an important target for exercise interventions.