Skeletal Muscle Energetics and Fatiguability in Older Individuals

This study is examining how muscles use energy and how quickly they get tired in older adults, including both people living with HIV (who are on stable treatment) and HIV-negative people, using MRI imaging. **You may be eligible if...** - You are 60 years old or older - If HIV-positive: you are on stable antiretroviral therapy with an undetectable viral load (less than 100 copies) - If HIV-negative: you are otherwise healthy and eligible **You may NOT be eligible if...** - You have contraindications to MRI (e.g., certain implants or pacemakers) - You have significant heart, lung, muscle, bone, or joint conditions that seriously limit your ability to exercise - You have significant vascular disease in the legs - You weigh more than 350 lbs - You have cognitive or speech difficulties that would prevent you from completing questionnaires or reporting fatigue Talk to your doctor to see if this trial is right for you.