Subjects of the proposed research will be between 21 and 80 years of age and living within a reasonable travel distance from the greater Washington D.C. area. Subjects will be recruited from the NIH/NIAMS IRP Lupus Clinics. All tests and exercise training will be conducted at the NIH Clinical Center. There will be a single treatment condition consisting of 12-weeks of supervised treadmill walking, three times a week, for 30 minutes per session, at an intensity of 70-80% of the subject s heart rate reserve.