None of the 21 interview participants were aware of physical activity guidelines for dementia risk reduction, and most lacked detailed procedural knowledge about the type, amount or intensity of activity required. Many assumed incidental activity was sufficient. This gap highlights the need for interventions to provide specific, accessible knowledge — including conceptual and procedural information from trusted sources — as a foundation for behaviour change.

In contrast to existing published literature on physical activity behaviour change, emotional regulation emerged as a particularly prominent theme in interviews. Participants described how depression and anxiety symptoms directly undermined their capacity to act on intentions, even when motivation and knowledge were present. Negative emotions, difficulties with emotional self-regulation and low confidence in psychological self-management skills created a vicious cycle of inactivity that is specific to this population and requires deliberate targeting in intervention design.

While participants broadly valued avoiding dementia, their commitment to personally adopting recommended physical activity was closely tied to their individual risk appraisals and beliefs about personal benefit. Many underestimated their own dementia risk, which was associated with reduced urgency to change behaviour. Interventions need to actively support realistic personal risk appraisal and help participants understand how physical activity can benefit them specifically, including for mood and anxiety symptoms.

Participants who were already active attributed their success to specific self-regulation skills: making activity habitual, monitoring their own behaviour, noticing immediate emotional and physical benefits, and adapting when health problems or life disruptions arose. Those who were inactive described low confidence in these same skills as a key barrier. Interventions should explicitly build behavioural regulation skills, particularly strategies to manage the cognitive and emotional difficulties common in this population.

Access to social opportunities — particularly a sense of accountability to a health professional, coach or peer — was consistently identified as a powerful facilitator of physical activity engagement. Professional support was additionally linked to overcoming fears of injury or health deterioration. Many participants also valued technology-based tools for self-monitoring and accountability. Interventions should provide structured opportunities for social connection, professional guidance and accessible accountability tools.

The final model, organised by the COM-B framework's three domains of Capability, Motivation and Opportunity, identifies five key mechanisms of action: being informed to enable change; individual attitudes and urgency for change; skills and confidence to make and enact intentions; access to social opportunities; and access to reliable and flexible resources. Importantly, these mechanisms interact and reinforce each other, meaning interventions that address multiple areas simultaneously are likely to be more effective than single-focus approaches.