Inclusion Criteria:

• * Aged ≥ 50years,
• * Sedentary lifestyle, defined by self-reported physical activity that breaks a sweat \<3 days/week, with no regular resistance exercise for 3 months preceding study,
• * Fatigued (≥2.0 on either of the first two screening items on the HIV-Related Fatigue Scale),
• * HIV infection, on prescribed HIV antiretroviral therapy for ≥ 12 months, with no current use (within 1 year) of older drugs with established mitochondrial toxicity (i.e., D4T, DDI, ZDV),
• * HIV-1 RNA level \< 200 copies/mL, for a minimum of 12 months prior to enrollment, with an allowed blip to 500 copies/mL presuming repeat assessments are below 200 copies,
• * Willing to participate in either assigned arm of a 16-week supervised exercise intervention 3 times weekly,
• * Thyroid Stimulating Hormone (TSH) within normal lab limits-Cell phone with ability to receive text messaging in order to participate in the biobehavioral maintenance intervention or ability to access to email daily
• * Ability and willingness of participant to provide informed consent and consent for access to medical record
• * COVID-19 vaccination and appropriate boosters received

Exclusion Criteria:

• * Weight over 450 pounds (due to limitations of the DXA machine)
• * Use of sex hormone therapy, if on for ≤3 months (stable doses for \>3 months will be permitted)
• * Use of other hormone replacement, if on for ≤ 3 months (stable doses \>3 months will be permitted)
• * Anemia (Hemoglobin ≤9 g/dL for women or ≤10 g/dL for men) due to contribution to fatigue,
• * Diagnosis of mitochondrial disease For participants undergoing the muscle biopsy only, use of anticoagulant therapy other than low dose aspirin that cannot be held for at least 7 days for the muscle biopsy. Aspirin and non-steroidal use will be permitted but will be held for 7 days prior to the muscle biopsy, and can be resumed following the biopsy.
• * Due to the expected fatigue associated with COVID-19 and potential infection risk, anyone with a diagnosis of COVID will not be eligible for enrollment until at least 30 days after symptom resolution and return to baseline level of function.
• * Active substance abuse or other factors that could prevent compliance or safety with study visits, at the discretion of the site investigator,
• * Reasons for medical exclusion, as determined by study PIs:
• * Uncontrolled hypertension defined as resting systolic blood pressure \>150 mmHg or diastolic blood pressure \>90 mmHg; participants who do not meet these criteria at first screening will be re-evaluated, including follow-up evaluation by their primary care provider with initiation or adjustment of anti-hypertensive medications,
• * Unstable ischemic heart disease (e.g., angina, ST segment depression) or serious arrhythmias at rest or during the graded exercise test without negative follow-up evaluation will be cause for exclusion; follow-up evaluation must include diagnostic testing (e.g., thallium stress test) with interpretation by a cardiologist,
• * New York Heart Association Class III or IV congestive heart failure, clinically significant aortic stenosis, uncontrolled angina, or uncontrolled arrhythmia,
• * Pulmonary disease requiring the use of supplemental oxygen at rest or with physical exertion,
• * Malignancy requiring chemotherapy or radiation therapy within 24 weeks prior to enrollment,
• * Poorly controlled diabetes, as evidenced by hemoglobin A1c \> 8.0, documented within 6 months of study visit,
• * Surgery/trauma/injury/fracture within 24 weeks prior to enrollment that, in the opinion of the study physician, may impact a subject's baseline functional testing and ability to exercise,
• * Balance impairments that may impact functional testing and ability to safely exercise as reported by the participant or in their medical record,
• * Orthopedic problems (e.g., severe osteoarthritis, rheumatoid arthritis) that greatly limit the ability to perform moderate intensity resistance exercise (e.g., unable to be properly positioned in exercise equipment or to have severely restricted range of motion even after modifications have been made),
• * Persons who, in the judgment of the study physician, appear to have unstable health or are incapable of safely participating in the exercise intervention.