For Exercise to Be Effective, Do I Have to Do Several Hours a Day, Seven Days a Week? Dr. Rebecca Manno busts this misconception by letting us know the benefits of any amount of exercise. In This VideoRebecca Manno, MD, MHSDr. Manno is an Assistant Professor of Medicine in the Division of Rheumatology. The focus of her research is the effect of inflammatory arthritis and vasculitis on muscle, strength, and function; particularly in older patients.