Human behaviours such as lifestyle habits are challenging to change and complex to study. Whether implementing interventions in health care settings or using digital platforms a thorough planning phase including an underpinning programme theory and undertaking a process evaluation are key phases for a better understanding of what works. 

I will present some of my experiences from behavioural intervention research. We followed the Medical Research Council guidance for evaluating complex interventions to undertake a process evaluation of a two-year pedometer intervention with or without counselling in primary care. The process evaluation included the delivery of the interventions, intervention dose, and patterns of behavior change. Further, we studied intervention mechanisms as perceived by the participants through qualitative interviews. For an upcoming real-world study, we have performed a formative research phase, including focus group interviews, a systematic review, and co-development of the intervention in close collaboration with a tech company.