Abstract
<p>Background: Physical activity (PA) counselling and sports coaching are more effective when professionals use self-determination theory-based need-supportive interaction. Existing interventions generally involve information provision and practical exercise, and show modest, short-term effects. Behaviour change science has rarely been incorporated, despite its potential to support sustainable change. Aims: This study systematically applies behaviour change science to develop an intervention to train professionals in motivational interaction behaviours. Methods: A four-step mixed-methods design included a needs assessment questionnaire (n=203), and pre-test acceptability questionnaires and group interviews (n=15). Systematic intervention development involved, 1) identifying target behaviours, determinants and behaviour change strategies, 2) formulating theory of change, 3) co-development of intervention materials, and 4) acceptability evaluation. Qualitative data were content analysed and means and medians of quantitative data (58 items, scale 1-5) were explored.Results: 1) We selected nine motivational interaction behaviours (e.g., open questions, clarifying expectations) alongside seven determinants (e.g., self-efficacy) and intervention strategies. 2) Habit and control theories informed self-monitoring, action and coping planning, and habit formation/disruption activities. The intervention was delivered via 3) an online platform, slide shows, videos and homework. 4) Overall acceptability was high after iterative optimisation. Prior to optimisation, self-insight maps had low overall acceptability (M = 2.8). Implementation intentions were rated acceptable (M = 3.6), but qualitative data revealed substantial misunderstandings concerning intervention coherence, perceived effectiveness, and self-efficacy.Conclusion: Quantitative-qualitative divergence in implementation intention data underlines the value of mixed-methods evaluation. Habit theory-based exercises show promise but feasibility and effectiveness testing are needed before conclusions about behavioural impact</p>