This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. An estimated 21 million people in the United States are affected by type 2 diabetes mellitus 1. In the U.S., ethnic minority groups like those served by our institution are disproportionately affected by obesity and type 2 diabetes 2, 3. Despite the wide array of pharmacological treatments now available, roughly half of all diabetic patients nationwide still have a hemoglobin A1c (HbA1c) level above 7% 4. The ADA recommends that all diabetic patients engage regularly in a minimum of 150 minutes per week of moderate-intensity aerobic activity 5. Sustained exercise trainingimproves glucose uptake and glycemic control 6, 7 in a dose-dependent and rapid fashion, demonstrable within as little as 12 hours after a single bout of intense exercise 8. However, it is also relatively transient if the exercise stimulus is not maintained, with a loss of insulin sensitization within ~72 hours after abrupt cessation of an exercise program 9, 10. The improvement in insulin sensitivity can be reproducibly demonstrated even in the absence of changes in body weight or adiposity, as shown in shorter-duration studies 11, 12. Chronic maintenance of regular physical activity not only contributes to weight loss and reduced adiposity, but also improves multiple cardiovascular risk factors 13-18, cardiovascular and overall mortality 19-24, a number of nonmetabolic \conditions 25-31, and psychosocial traits 32-35. Exercise prescriptions can be customized to suit a patient's unique preferences and lifestyle, which leads to improved long-term compliance 36. Direct costs associated with self-initiated physical activity programs may also be favorable compared to other therapies. Specific Aim #1: To compare the effects of self-initiated exergaming versus self-initiated treadmill exercise on changes in glycemic control in adult patients with type 2 diabetes mellitus. Specific Aim #2: To compare the effects of self-initiated exergaming versus self-initiated treadmill exercise on changes in body composition, aerobic fitness, cardiovascular risk factors, attendance and sustainability of physical activity, and psychological correlates of exercise behavior, in adult patients with type 2 diabetes mellitus.