and indirect medical costs in the United States. Even small increases in regular moderate-to-vigorous physical activity, especially if made by the least physically active individuals, would appreciably reduce the nation’s direct and indirect medical costs. Quantification of the costs attributable to insufficient physical activity was beyond the scope of this Committee. It is clear, however, that the cost reductions would be large by any standards. More difficult to quantify, but equally as important, are the benefits associated with how individuals feel every day and the energy and vitality they have to carry out their daily lives. Placing dollar estimates on improved cognition across the full life span, better quality of life, fewer symptoms of depression and anxiety, enhanced quality of sleep, and improved physical function is difficult. In addition, monetizing Part A. Executive Summary 2018 Physical Activity Guidelines Advisory Committee Scientific Report A-7 these benefits likely cannot adequately describe the intangible societal benefits that derive from a happier and more energetic population. THE FUTURE The field of physical activity and public health has matured markedly in the past 10 years, and it will continue to develop at a rapid pace. Using the existing extensive scientific foundation and aided by recent technological advances, increases in knowledge about the relationships between physical activity and a wide variety of health and quality of life outcomes will surely continue. The Committee has described current evidence and recent gains in knowledge, but recognizes that in the near future, the field will generate more information about the benefits of physical activity and the types and volumes that provide those benefits. In addition, gains in the area of physical activity promotion are accumulating rapidly. Transferring this new knowledge into public health practice has the potential to improve the health of the American public to an unprecedented level. At the same time, the Committee recognized that important gaps in knowledge still remain. It prepared a substantial list of topic-specific research recommendations. Six overarching recommendations are provided here. • Determine the independent and interactive effects of physical activity and sedentary behavior on multiple health outcomes in youth, adults, and older adults. • Determine the role and contribution of light-intensity physical activity alone or in combination with moderate-to-vigorous physical activity to health outcomes. • Identify effective intervention strategies for increasing physical activity through actions in multiple settings in youth, adults, and older adults. Determine how the effectiveness of interventions differs by sex, age, race, ethnicity, socioeconomic status, and other factors. • Strengthen the understanding of dose-response relationships between physical activity and multiple health outcomes in youth, adults, and older adults, and especially during the life transitions between these categories. • Expand knowledge of the extent to which the relationships between physical activity and health outcomes are modified by demographic factors, including sex and race/ethnicity. • Develop instrumentation and data collection systems that will enhance physical activity surveillance systems in the United States. Part B. Introduction 2018 Physical Activity Guidelines Advisory Committee Scientific Report In 2008, the U.S. Department of Health and Human Services (HHS) released the first edition of the Physical Activity Guidelines for Americans. 1 The Guidelines provides science-based advice on how physical activity can help promote health and reduce the risk of chronic disease. The Guidelines serves as the benchmark and primary, authoritative voice of the federal government for providing sciencebased guidance on physical activity, fitness, and health for Americans. It provides a foundation for federal recommendations and education for physical activity programs for Americans, including those at risk of chronic disease. The Guidelines were developed using information from a Physical Activity Guidelines Advisory Committee,2 similar to the expert committees formed for the Dietary Guidelines for Americans3 process. This committee mechanism was recognized as an effective approach to obtain a comprehensive and systematic review of the science, which contributes to successful federal implementation as well as broad public acceptance of the Guidelines. Part B. Introduction 2018 Physical Activity Guidelines Advisory Committee Scientific Report B-2 In 2013, five years after the Guidelines was released, HHS developed the Physical Activity Guidelines Midcourse Report: Strategies to Increase Physical Activity Among Youth. 4 This report built on the 2008 Guidelines1 by focusing on strategies to help youth achieve the recommended 60 minutes of daily physical activity in a variety of settings, including school, preschool and childcare, community, family and home, and primary care. The 2008 Guidelines 1 was developed because of strong evidence that regular physical activity promotes health and reduces risk of many chronic diseases, including heart disease, diabetes, and several cancers. This evidence base continues to grow; thus, in December 2015 HHS began the process of developing the second edition of the Physical Activity Guidelines by calling for nominations to the 2018