The Effect of Theory-driven Physiotherapy on Physical Activity in Knee OA.

Knee osteoarthritis (OA) is a leading cause of pain, disability, and reduced physical functioning worldwide. Although physiotherapy and physical activity are recommended as first-line treatments, many individuals with knee OA do not achieve or maintain recommended levels of physical activity. As a result, the benefits of evidence-based physiotherapy are often not fully realized. To improve physical activity participation, effective behaviour change interventions are needed. Theory-informed interventions have the potential to enhance physiotherapy outcomes by targeting the psychological determinants that influence physical activity behaviour. One well-established framework is the Theory of Planned Behaviour (TPB), which proposes that behaviour is primarily influenced by behavioural intention, attitude, subjective norms, and perceived behavioural control. To translate these determinants into intervention content, behaviour change techniques (BCTs) can be systematically selected using tools such as the Behaviour Change Intervention Ontology (BCIO), Mechanisms of Action Ontology (MoAO), and Theory and Techniques Tool (TaTT). This approach may improve the effectiveness and sustainability of behaviour change interventions. The present study therefore aims to evaluate the potential of a TPB-based behaviour change intervention as an addition to guideline-recommended physiotherapy for individuals with knee OA. The primary objective is to determine whether this theory-driven intervention can improve physical activity levels and reduce sedentary behaviour. A secondary objective is to explore the behavioural mechanisms through which these changes occur. The study will employ a randomized, concurrent, multiple-baseline single-case experimental design (SCED). Participants with knee OA will receive a six-week physiotherapy intervention consisting of usual guideline-based care supplemented with a TPB-based behaviour change component. Physical activity and sedentary behaviour will be continuously assessed using ActiGraph accelerometers. In addition, behavioural determinants, pain, and functional limitations will be repeatedly measured to evaluate potential mechanisms of action and clinical effects. Findings from this study may contribute to the development of more effective, theory-informed physiotherapy interventions aimed at promoting sustainable physical activity behaviour in people with knee OA.