Selection and justification of performance-related measures in exercise trials for people with chronic low back pain: A scoping review and content analysis

BACKGROUND: Chronic low back pain (CLBP) is the leading cause of years lived with disability worldwide. Although exercise is a first-line, cost-effective treatment for CLBP, no single exercise modality has proven superior, suggesting uncertainty around the mechanisms linking exercise to clinical outcomes. AIM: To identify the performance-related measures used to assess physical and physiological characteristics (including strength, endurance, mobility, stability, motor control, and muscle morphology) in exercise trials for chronic low back pain, and to examine the rationales and proposed mechanisms used to justify their selection. DESIGN: Scoping review with content analysis. METHODS: We identified relevant clinical trials from a Cochrane review of exercise for CLBP and updated their search to identify newer trials. Eligible randomised controlled trials reporting both performance and clinical outcomes were synthesised using content analysis. FINDINGS: Across 223 trials, 150 unique performance measures were identified, demonstrating substantial theoretical and methodological heterogeneity. Rationales provided were organised into 5-themes (posture and positional, stability and control, fitness properties, psychosocial, and other) with 17-sub-themes. Rationales were mapped against the 17 sub-themes in 1706 unique combinations across all included studies, highlighting a lack of consistency with the proposed mechanisms for how/why exercise may address key clinical outcomes for CLBP. CONCLUSION: The findings highlight a lack of theoretical coherence in how performance-related measures are conceptualised and measured in exercise trials for CLBP, highlighting the need for more theory-informed study designs.