In Part 2 of the study, a portion of participants from Part 1 of the study who are infected with HIV will be randomly assigned to take part in a 12-week exercise program or a control group. At a baseline study visit, all participants will undergo a medical history review, fitness testing, body measurements, muscle and fat measurements, blood collection, echocardiogram, questionnaires to assess quality of life and activity levels, and an ultrasound of the brachial artery (on the upper arm) and carotid artery (on the neck) to measure artery size.