STICK2IT - Understanding Why People Do or Do Not Stick With Exercise Treatment for Achilles Tendinopathy

Achilles tendinopathy (AT) is a common musculoskeletal condition characterised by pain, stiffness and impaired function of the Achilles tendon. Although progressive tendon-loading exercise is recommended as first-line treatment and has demonstrated efficacy in controlled research settings, outcomes in routine clinical practice are often slower, incomplete and variable. A key explanation for this discrepancy is that the effectiveness of loading-based rehabilitation depends on sustained engagement over time. In real-world NHS care, where treatment is largely delivered through supported self-management with limited supervision, patient adherence to prescribed exercise programmes becomes the primary mechanism through which treatment benefit is realised.

Adherence to rehabilitation is a complex behaviour influenced by interacting psychological, social and environmental factors. Existing research in Achilles tendinopathy has identified a range of commonly reported challenges, including fear of causing harm, uncertainty about exercising in the presence of pain, low confidence in performing or progressing exercises, competing life demands, and fluctuating motivation. These determinants are likely to be further shaped by contextual factors such as multimorbidity, socioeconomic constraints, cultural influences and health literacy. Despite this, current evidence remains largely descriptive and lacks a systematic, theory-informed structure that explains how these factors influence behaviour or how they might be targeted in intervention development.

This study addresses this gap by applying a behavioural science approach to understanding adherence. Specifically, it uses the Theoretical Domains Framework (TDF), an integrative framework that synthesises constructs from multiple behaviour change theories into a comprehensive set of domains. The TDF provides a structured method for identifying the underlying mechanisms that influence behaviour and is widely used in implementation and intervention development research. In this study, the framework will be used to organise behavioural determinants influencing engagement with progressive tendon-loading exercise and to support identification of modifiable targets for intervention.

A qualitative design using semi-structured interviews has been selected to enable in-depth exploration of participants' lived experiences of rehabilitation. This approach allows for the capture of nuanced accounts of how individuals interpret their symptoms, respond to exercise-related pain, integrate rehabilitation into daily life, and interact with healthcare services. It is particularly suited to investigating complex behaviours such as adherence, where individual context and meaning play a central role.

Data will be analysed using an abductive thematic analysis approach, combining inductive and deductive processes. Initially, an inductive analysis will identify patterns of meaning within the data, generating themes that reflect barriers and facilitators to adherence as described by participants. This stage ensures that findings remain grounded in lived experience rather than being constrained by pre-existing theory. Subsequently, these themes will be mapped onto the domains of the TDF to provide a structured, theory-informed interpretation of the behavioural determinants identified.

The use of an abductive approach enables both discovery and explanation: it allows new insights to emerge from the data while also situating those insights within an established theoretical framework. This is particularly important for translating qualitative findings into actionable intervention components. By linking identified determinants to theoretical domains, the study will support identification of potential mechanisms of action that can be targeted through behaviour change strategies.

Following mapping, determinants will be prioritised based on their perceived importance, frequency, and relevance to behaviour change. This prioritisation process will involve interpretive discussion within the research team, incorporating clinical expertise, methodological input, and perspectives from patient and public contributors. The aim is to identify a subset of key domains that represent meaningful and potentially modifiable influences on adherence in the context of NHS physiotherapy.

The study places particular emphasis on understanding adherence within the context of underserved populations. Behavioural determinants are not experienced uniformly across populations, and factors such as socioeconomic deprivation, multimorbidity, cultural context, and access to resources may shape both the nature and impact of barriers to engagement. By ensuring that these perspectives are represented and considered in analysis, the study aims to produce findings that are relevant to real-world service delivery and that support more equitable approaches to rehabilitation.

The outputs of this study will provide a structured, theory-informed understanding of the behavioural determinants that influence adherence to progressive tendon-loading exercise in Achilles tendinopathy. This will form the foundation for subsequent intervention development work, in which identified determinants will be translated into targeted strategies to support engagement with rehabilitation. These strategies may include educational, behavioural, and service-level components designed to address identified barriers and enhance facilitators within routine care pathways.

Importantly, the study is designed as an early-stage component within a broader programme of research. Its primary function is to generate the behavioural evidence required to inform intervention design, consistent with guidance for developing complex interventions. As such, it does not seek to test effectiveness but rather to establish what needs to change, for whom, and through which mechanisms, in order to improve adherence.

In the longer term, improving adherence to evidence-based rehabilitation has the potential to enhance patient outcomes, reduce persistence of symptoms, and improve efficiency within musculoskeletal services. By grounding intervention development in both behavioural theory and lived experience, the study aims to contribute to the design of more effective, acceptable and equitable approaches to supporting patients with Achilles tendinopathy in routine NHS practice.