Exploring working mechanism of an Implementation Strategy Bundle on the implementation of a lifestyle intervention for community-dwelling older adults: Process evaluation of a stepped wedge trial

Background : A theory- and practice-based implementation strategy bundle (ISB) was developed to support physical therapists and dieticians during implementation of the combined lifestyle intervention ProMuscle for community-dwelling older adults in multiple community-care settings. Alongside a 42-week hybrid type III stepped-wedge randomized cluster implementation effectiveness trial, a process evaluation was conducted to explore possible working mechanisms of the ISB on the adoption, reach, and fidelity of ProMuscle by describing a causal pathway. Additionally, barriers and facilitators for the use of the ISB were identified. Methods : During the 6-week transitional period in which clusters transitioned from the control to the intervention group and at the end of the 42-week trial, (group)interviews were held with physical therapists and dieticians. Interview guides were informed by the RE-AIM framework and supplemented with quantitative data from surveys and ISB tracking activity. Interviews were transcribed and thematically analyzed. Insights from the process evaluation informed a causal pathway diagram and the identification of barriers and facilitators for the use of the ISB. Results : Twenty-five physical therapists and dieticians were interviewed during the transitional period, and fifteen participated in the group interviews at the end of the trial. The causal pathway diagram revealed that individual factors (knowledge and beliefs about the intervention, convincing others, and networking), and organizational- and system-level factors (facilitation, collaboration, and support) moderated the influence of the ISB on the implementation outcomes. Particularly organizational and system-level factors could not always be addressed by individual professionals. The fidelity of the ISB was low, according to HCPs, due to timing of receiving the ISB and lack of education on its use. Conclusion : The results highlight the complexity of real-world implementation in multiple community-care settings and address the need for organizational and policy-level facilitation to enhance the implementation, sustainment, and scale-up of lifestyle interventions for community-dwelling older adults. Additionally, low fidelity of the ISB probably contributed to the non-significant effect of the ISB on the adoption of ProMuscle. Future implementation studies should take the timely delivery of an ISB into account and provide adequate education to healthcare professionals about the use of implementation strategies. Trial registration: ClinicalTrials.gov (NCT05672004) registered at 12/07/2022 https://clinicaltrials.gov/ct2/show/NCT05672004