High-intensity Exercise After Treatment

Inclusion Criteria: * Adult female (aged 19 or older) * First, primary diagnosis of Stage I-IIIa breast cancer * Hormone receptor positive (ER+ and/or PR+) diagnosis * Human epidermal growth factor receptor 2 negative (HER2-) diagnosis * Completed primary adjuvant treatment (i.e., surgery, chemotherapy, and/or radiation therapy) * Currently prescribed an aromatase inhibitor * No evidence of possible cognitive impairment as assessed using the Telephone Interview of Cognitive Status (TICS-M; score \>21) * Sedentary except for casual lifestyle recreation. This is defined as self-reporting 20+ minutes of exercise physical activity on 2 or fewer days per week within the previous six months. * Receive physician's clearance to participate in an exercise program * Agree to be randomized * Fully vaccinated for COVID-19 ≥2 weeks prior to participation * Provide written informed consent to participate in study Exclusion Criteria: * Males. * Stage 0 breast cancer diagnosis or metastatic disease * Currently receiving chemotherapy or radiation therapy for any cancer * Scheduled to receive breast surgery (e.g., mastectomy, reconstructive surgery) during the study period * Second cancer diagnosis (excluding non-invasive skin cancers; including breast cancer recurrence) * Self-report an 20+ minutes of exercise physical activity on 3+ days per week for the previous 6 months * Pregnant or plan to become pregnant during study period. * Is not cleared to participate in exercise by a physician. * Enrolled in another physical activity program * Unable to cycle on a stationary bike * Unwilling to complete study requirements * History of stroke, transient ischemic attack, other neurological disorders, or brain surgery involving tissue removal * Clinically significant TICS-M score (\<21) during baseline procedures * Not fully vaccinated for COVID-19