Optimization of a Behavioral Intervention to Increase Physical Activity in Older Adults Living With HIV

Inclusion Criteria: 1. HIV positive: defined by HIV antibody, detectable HIV RNA in plasma, or a note from the participant's HIV care provider. 2. Must be on continuous antiretroviral therapy (ART) for \> 3 months, as assessed via self-report. 3. Low PA: defined as self-report of \< 90 minutes of moderate-vigorous PA (MVPA) per week in the previous 3 months AND less than 14 hours per week of sustained walking in the previous 4 weeks. 4. Medically cleared for moderate PA. If participants report a) a history of cardiovascular disease including known coronary artery disease, peripheral vascular disease, heart failure, or stroke; or b) chest pain, shortness of breath, or dizziness or syncope either at rest or during activity in the past 3 months, then they must have medical clearance by a physician or primary care provider. 5. Age 50 years or older. 6. Proficiency in English: sufficient to engage in informed consent, understand assessments and materials provided, and engage and use Fitbit application (all materials provided in English). 7. Capacity to consent, documented by acceptable answers in a consent "teach-back" process. 8. Score of greater than 16 on the MOCA 9. Able to ambulate without assistive devices 10. Ability to use the FitBit application, as demonstrated to study staff. Exclusion Criteria: * Exclusion Criteria 1. Medical conditions or physical or neurocognitive limitations that interfere with PA or study participation. 2. Hazardous substance use, assessed via a score ≥15 on the Alcohol Use Disorders Identification Test (AUDIT) or ≥6 on the Drug Abuse Screening Test (DAST).