Implementers' perceptions of barriers and facilitators in the implementation setting is associated with physical activity changes among participants of a planning intervention.

Objective: The present study applies the Consolidated Framework for Implementation Research to investigate the associations between: (1) implementation process indicators, namely implementers' perceptions of barriers/facilitators in the outer and inner implementation setting, (2) implementer self-efficacy and (3) changes in moderate-to-vigorous physical activity (MVPA) among participants of two intervention studies (physical activity planning interventions versus control [education] conditions).

Methods and measures: Data collected among 372 participants (66.9% women; 9-86 years old) were matched with implementers' data (n = 21, 100% women, 25-46 years old). MVPA was assessed with accelerometers at the baseline and 14-month follow-up. Implementation process indicators were self-reported by implementers.

Results: We found significant interaction effects of Time x Implementation Process indicators on MVPA. Participants who were supported by implementers who perceived barriers/facilitators in the inner and outer implementation setting as adequately addressed, maintained their MVPA at 14-month follow-up. A decline in MVPA was found among participants supported by implementers perceiving lower adequacy of addressing respective barriers/facilitators. Implementer self-efficacy was unrelated to MVPA of participants of intervention studies.

Conclusions: Implementers' positive evaluation of the ways barriers/facilitators were addressed in the implementation setting may protect participants (regardless of their intervention or control group assignment) from a decline in MVPA time.