Part G. Needs for Future Research. At least two Committee members who were not members of the drafting Subcommittee and federal staff liaisons reviewed each chapter. Report Structure Reflecting the Subcommittee and Work Group structure, the bulk of the report consists of 11 sciencebased chapters that summarize the evidence assessed and evaluated by the Committee. Ten chapters correspond to the work of the nine Subcommittees—the Exposure Subcommittee’s findings are split into two chapters—and one chapter covers the work of the Pregnancy and Postpartum Work Group. In addition to summarizing the evidence relating physical activity to individual health outcomes, one of the Committee’s major goals was to integrate the scientific information on the relationship between physical activity and health and to summarize it in a manner that could be used effectively by HHS to develop the Physical Activity Guidelines and related statements. This information is contained in Part D. Integrating the Evidence. Part B. Introduction 2018 Physical Activity Guidelines Advisory Committee Scientific Report B-7 CONTENTS AND ORGANIZATION OF THE SCIENTIFIC REPORT The report starts with a Membership List of the Physical Activity Guidelines Advisory Committee members, consultants, and federal staff to acknowledge the individuals involved in the development of this report. There are four major components in the report. The first component provides essential background and synthesis information and includes: • Part A. Executive Summary provides an executive summary of the entire report. • Part B. Introduction provides a brief background on the rationale for updating the Physical Activity Guidelines for Americans and an explanation of the Committee’s formation, structure, and process to develop its report. • Part C. Background and Key Physical Activity Concepts explains the concepts and terminology that provide the foundation for the report’s content and framing, including those relating to physical activity, sedentary behavior, dimensions of physical activity, physical fitness, and measurement. • Part D. Integrating the Evidence synthesizes the Committee's findings about the relation of physical activity to a broad array of health outcomes. • Part E. Systematic Review Literature Search Methodology explains the process used to systematically review the literature review questions. The second component, Part F. The Science Base, includes 11 chapters organized into four sections that review and summarize the scientific literature relating physical activity to individual health-related outcomes and populations: New Issues in Defining Physical Activity • Chapter 1. Physical Activity Behaviors: Steps, Bouts, and High Intensity Training • Chapter 2. Sedentary Behavior Physical Activity and Selected Health Outcomes • Chapter 3. Brain Health • Chapter 4. Cancer Prevention • Chapter 5. Cardiometabolic Health and Prevention of Weight Gain • Chapter 6. All-cause Mortality, Cardiovascular Mortality, and Incident Cardiovascular Disease Physical Activity Considerations for Selected Populations Part B. Introduction 2018 Physical Activity Guidelines Advisory Committee Scientific Report B-8 • Chapter 7. Youth • Chapter 8. Women Who are Pregnant or Postpartum • Chapter 9. Older Adults • Chapter 10. Individuals with Chronic Conditions Promoting Physical Activity • Chapter 11. Promoting Regular Physical Activity The third component, Part G. Needs for Future Research provides the Committee's collective recommendations about key areas of research that could address gaps they encountered and further enhance the science base on physical activity and health. The fourth component, Part H. Appendices, includes 1) glossary of terms, 2) list of Subcommittee and Work Group assignments, 3) biographical sketches of Committee members, and 4) description of the public comment process with a link to the public comment database. REFERENCES 1. U.S. Department of Health and Human Services. 2008 Physical Activity Guidelines for Americans. Washington, DC: U.S. Department of Health and Human Services; 2008. https://health.gov/paguidelines/guidelines. Published 2008. Accessed September 22, 2017. 2. Physical Activity Guidelines Advisory Committee. Physical Activity Guidelines Advisory Committee Report, 2008. Washington, DC: U.S. Department of Health and Human Services; 2008. https://health.gov/paguidelines/guidelines/report.aspx. Published 2008. Accessed September 22, 2017. 3. U.S. Department of Health and Human Services; U.S. Department of Agriculture. 2015–2020 Dietary Guidelines for Americans. 8th ed. http://health.gov/dietaryguidelines/2015/guidelines. Published December 2015. Accessed January 11, 2018. 4. Physical Activity Guidelines for Americans Midcourse Report Subcommittee of the President’s Council on Fitness, Sports & Nutrition. Physical Activity Guidelines for Americans Midcourse Report: Strateg The field of physical activity and public health has been developing at a rapid pace during the past several decades. During the 1950s and 1960s, two scientific areas – exercise science and epidemiologic Part C. Background and Key Physical Activity Concepts 2018 Physical Activity Guidelines Advisory Committee Scientific Report C-