Using self-determination theory to understand and improve recruitment for the Coaching for Healthy Ageing (CHAnGE) trial.

Background: Intervention trials promoting physical activity among older people frequently report low and unrepresentative recruitment. Better understanding of reasons for participation can help improve recruitment. This study explored why participants enrolled in the Coaching for Healthy Ageing (CHAnGE) trial, including how their decision was influenced by recruitment strategies. CHAnGE was a cluster randomised controlled trial testing the effectiveness of a healthy ageing program targeting inactivity and falls. Seventy-two groups of people aged 60+ were recruited from community organisations via informal presentations by the health coaches.

Methods: We conducted a secondary thematic analysis of interview data from our wider qualitative evaluation in which 32 purposively sampled trial participants took part in semi-structured interviews about their experiences of CHAnGE. Data relating to recruitment and participation were analysed inductively to identify themes, then a coding framework comprising the core constructs from self-determination theory-autonomy, competence and relatedness-was used to explore if and how this theory fit with and helped to explain our data.

Results: Recruitment presentations promoted the CHAnGE intervention well in terms of addressing value expectations of structured support, different forms of accountability, credibility, achievability and, for some, a potential to enhance social relationships. Participation was motivated by the desire for improved health and decelerated ageing, altruism and curiosity. These factors related strongly to self-determination concepts of autonomy, competence and relatedness, but the intervention's demonstrated potential to support self-determination needs could be conveyed more effectively.

Conclusions: Findings suggest that recruitment could have greater reach using: 1. Strengths-based messaging focusing on holistic gains, 2. Participant stories that highlight positive experiences, and 3. Peer support and information sharing to leverage altruism and curiosity. These theory-informed improvements will be used to increase participation in future trials, including people in hard-to-recruit groups. They may also inform other physical activity trials and community programs.