Recently, the US Department of Health and Human Services issued its first ever physical activity guidelines, which were developed because ‘‘we clearly know enough now to recommend that all Americans . . . engage in regular physical activity to improve overall health and to reduce risk of many health problems.’’1 The current weekly recommendation (2.5 hours of moderate aerobic physical activity, 1.25 hours of vigorous aerobic physical activity, or an equivalent combination of moderate and vigorous aerobic physical activity plus additional muscle strengthening activities on 2 or more days) has increased from the 1995 recommendation issued by the American College of Sports Medicine and the Centers for Disease Control and Prevention of at least 30 minutes of moderate physical activity on most days of the week. The Mayo Clinic lists several medical benefits of regular physical activity on its Web site, including weight management, increased cardiovascular function, prevention and control of chronic diseases, and improvement in sleep.2 Number 1 on its list is the positive effect of physical activity on psychological well-being. Major depressive disorder (MDD) is characterized by periods of depressed mood and/or anhedonia (ie, loss of interest or pleasure) that last at least 2 weeks in combination with several somatic symptoms (changes in appetite, sleep, energy level, and psychomotor function) and cognitive disturbances (feelings of worthlessness or inappropriate