Planning Actions for Consistent Engagement

The goal of this clinical trial is to evaluate whether different approaches to action planning can promote physical activity (PA) habits, increase PA behavior, and improve cognitive functioning in older adults who are currently inactive or insufficiently active. The main questions it aims to answer are: 1. Does a trial-and-error approach to PA action planning lead to greater improvements in PA habits, PA behavior, and cognitive functioning compared to standard PA planning or non-PA planning? 2. Does greater consistency and successful enactment of action plans result in more substantial changes in PA habits, behavior, and cognitive functioning? Researchers will compare three groups to determine which planning approach yields superior outcomes.: 1. Non-PA planning (generic weekly planning) 2. PA planning (weekly planning for PA) 3. PA trial-and-error planning (weekly PA plans followed by preferred plan adoption) Participants will: 1. Wear Fitbit monitors continuously for 9 months to track PA behavior 2. Complete mobile cognitive assessments daily for 7 days before the intervention, monthly during the intervention, and at follow-up 3. Create action plans and report on PA habits, intentions, and plan enactment weekly during the intervention and at follow-up