ObjectiveTherapeutic exercises are a core treatment for low back pain (LBP), but it is uncertain how rehabilitative exercise facilitates change in outcomes. Realist reviews explore how the context (C) of certain settings or populations and underlying mechanisms (M) create intended or unintended outcomes (O). Our objective was to explore and understand the behavioural mechanisms by which therapeutic exercise creates change in outcomes of adherence, engagement and clinical outcomes for patients with LBP.MethodsThis was a realist review reported following the Realist and Meta-narrative Evidence Syntheses: Evolving Standards guidance. We developed initial programme theories, modified with input from a steering group (experts, n=5), stakeholder group (patients and clinicians, n=10) and a scoping search of the published literature (n=37). Subsequently, an information specialist designed and undertook an iterative search strategy, and we refined and tested CMO configurations.ResultsOf 522 initial papers identified, 75 papers were included to modify and test CMO configurations. We found that the patient–clinician therapeutic consultation builds a foundation of trust and was associated with improved adherence, engagement and clinical outcomes, and that individualised exercise prescription increases motivation to adhere to exercise and thus also impacts clinical outcomes. Provision of support such as timely follow-up and supervision can further facilitate motivation and confidence to improve adherence to therapeutic exercises for LBP.ConclusionsEngagement in and adherence to therapeutic exercises for LBP, as well as clinical outcomes, may be optimised using mechanisms of trust, motivation and confidence. These CMO configurations provide a deeper understanding of ways to optimise exercise prescription for patients with LBP.