Understanding responsiveness to an exercise intervention for people with persistent low back pain and lateral abdominal muscle impairments. A mixed methods study.

Background: Exercise consistently demonstrates a small effect size for patients with persistent low back pain (PLBP). Determining patient characteristics that influence intervention responsiveness may improve treatment allocation and effect sizes. An exercise intervention for patients with PLBP and maladaptive changes in lateral abdominal muscle (LAM) contraction was recently trialed.

Objective: To identify factors predicting responsiveness to an exercise intervention for patients with PLBP and why.

Methods: This was a secondary mixed methods analysis of results from a feasibility randomized controlled trial with 50 participants. The 12-week program included individualized motor control and graded activity exercise. Regressions were performed to understand potential associations between characteristics (demographic, condition-specific signs and symptoms, compliance with exercise, and beliefs about exercise) and outcomes (pain, function, disability, and LAM contraction). Interview transcripts were analyzed for characteristics unique to participants that responded most and least to the intervention. Data was integrated for complementarity.

Results: At baseline, females, participants with lower BMIs, decreased chronicity, fewer areas of pain, who had less previous interactions with healthcare professionals, and who were more positive about the potential for exercise to improve their pain had greater responsiveness (Adjusted R² ranged from 0.17 to 0.66). During and after the program, increased physical activity levels was a positive predictor.

Conclusion: Responsiveness to the intervention may have been mediated by several baseline factors which may have affected participants' engagement with the intervention and continuation with exercise post intervention. Such characteristics may assist clinicians identifying whether this may be an appropriate intervention for patients with PLBP.