Strengths and limitations
Previous studies applying the TFA to explore intervention development have primarily been qualitative studies [Increasing acceptability is important when developing interventions iteratively, and in line with recognised guidance for intervention development. We present an experimental approach that allows researchers to target specific TFA domains in future iterations of interventions (e.g. addressing perceived effort to engage with interventions). Another strength of our process is the involvement of stakeholders in the design and modification of interventions, allowing participants to provide specific feedback on an existing intervention with the overarching aim of increasing intervention acceptability and feasibility [