Inclusion Criteria:  Adult female with first-time, primary diagnosis of Stage I-IIIa breast cancer Post-menopausal at diagnosis (no menses for 12 mo.) Post-surgery and completed primary adjuvant treatments (i.e., radiation and/or chemotherapy) within 6-24 months of study enrollment (current hormonal therapy eligible) Sedentary except for casual lifestyle recreation. Sedentary will be defined as reporting 20+ minutes of exercise PA on 2 or fewer days per week within previous 6 months Physician's clearance to participate in an exercise program Agree to be randomized to exercise or control Telephone Interview of Cognitive status (TICS-M) performance above impaired range (>21) Provide informed consent Fully vaccinated for COVID-19  Exclusion Criteria:  Scheduled to receive breast surgery during study Second cancer diagnosis (excluding non-invasive skin cancers; including breast cancer recurrence) History of stroke, transient ischemic attack, neurological disorders, or brain surgery involving tissue removal Unable to walk without assistance or devices Clinically significant TICS-M Unwilling to complete study requirements Contraindications to fMRI in accordance with institutional safety protocols Enrolled in another physical activity program Not fully vaccinated for COVID-19