Abstract-In this review, our first purpose is to provide an overview of existing physical activity intervention research, focusing on subpopulations and intervention modalities. Our reviews within each area are not exhaustive or quantitative, as each area has been reviewed in more depth in numerous other reports. Instead, our goal is to provide a single document that provides a qualitative overview of intervention research that emphasizes selected topics of particular importance for improving the population-wide impact of interventions. Therefore, in synthesizing this vast literature, we begin with existing reviews of physical activity research in each area and incorporate in our discussions recent reports of well-designed individual physical activity intervention studies that expand the existing research base and/or target new areas of research. Our second purpose is to offer new ideas and recommendations to improve the state of the science within each area and, where possible, to propose ideas to help bridge the gaps between these existing categories of research. Key Words: AHA Scientific Statements Ⅲ exercise Ⅲ health behavior Ⅲ intervention studies Ⅲ metabolism Ⅲ motor activity S edentary behavior has been identified as one of the leading preventable causes of death, 1 and an inverse linear relationship exists between volume of physical activity behavior and all-cause mortality. 2 Moreover, participation in regular physical activity decreases the risk of cardiovascular disease, 3 type 2 diabetes mellitus, 4 osteoporosis, 5 depression, 6 obesity, 7 breast cancer, 8 colon cancer, 9 and falls in older adults. 6 Given the numerous health benefits of physical activity participation, various public health guidelines have been published on the recommended volume and intensity of physical activity for healthy adults. The American Heart Association, the US Surgeon General, the Centers for Disease Control and Prevention (CDC), and the American College of Sports Medicine recommend at least 30 minutes per day of at least moderate-intensity physical activity on most, and preferably all, days of the week. 10 -12 Similar guidelines have been adopted for children, 13 although other consensus panels have recommended one 14,15 or more 16 hours of physical activity per day for children. The CDC, American College of Sports Medicine, and Surgeon General further state that physical activity may be incorporated into one's everyday lifestyle and that the daily physical activity requirements may be accumulated over the course of the day in short bouts of 10 to 15 minutes. Finally, the US Department of Agriculture hasThe American Heart Association makes every effort to avoid any actual or potential conflicts of interest that may arise as a result of an outside relationship or a personal, professional, or business interest of a member of the writing panel. Specifically, all members of the writing group are required to complete and submit a Disclosure Questionnaire showing all such relationships that might be perceived as real or pote...