The Role of Flexibility in Predicting Health and Disease Progression in Patients with Chronic Health Conditions: A Systematic Review and Meta-Analysis​

Background Flexibility is widely recognised as a core component of health-related physical fitness, yet its value as an independent predictor of future health outcomes remains uncertain. Objective To systematically review and meta-analyse prospective cohort studies examining associations between flexibility and future health outcomes in adults with chronic conditions, emphasising clinically meaningful applications and identifying research gaps. Methods We systematic searched MEDLINE, Embase, Emcare, CINAHL Complete, and SPORTDiscus (January 2005–April 2025). Eligible studies were prospective cohorts assessing objectively measured flexibility or joint range of motion (ROM) against subsequent health or disease-specific outcomes in adults (≥18 years) with diagnosed chronic conditions. Risk of Bias was assessed using the CLARITY Group tool, and certainty of evidence was evaluated using GRADE, focussing on clinical relevance. Results Thirty-five studies (n=19 239; 53% female, mean age 55.7±14.5 years, median follow-up 2.0 years [range 0.25 to 15 years]) across 14 conditions were included. Substantial heterogeneity precluded pooling of results. A single meta-analysis in patients with hip and/or knee osteoarthritis (OA) provided moderate certainty of evidence of no association between flexibility and pain, stiffness, or physical function ( r =0.14; 95%CI: -0.03–0.29, p = 0.09). Narrative synthesis indicated that reduced knee extension ROM predicted radiological disease progression and total knee replacement in knee OA, while the Bath Ankylosing Spondylitis Metrology Index (BASMI) reliably tracked disease progression in axial spondyloarthritis. No longitudinal evidence was identified for major chronic conditions such as cardiovascular disease, diabetes, cancer, chronic respiratory diseases, obesity, or osteoporosis, highlighting critical research gaps. Conclusion Current evidence offers limited support for flexibility as a prognostic marker in chronic conditions. Condition-specific, multi-joint assessments (e.g., BASMI or joint-specific ROM) may provide greater clinical utility, but high-quality longitudinal studies are urgently needed to determine whether flexibility can meaningfully guide prognosis and inform clinical decision making. Trial Registration PROSPERO CRD420251029178.