Physical Exercise and Health, 1: An Overview of Terminology, Guidance, Benefits, and Risks

Regular physical activity in any form is important for health; nevertheless, more than a quarter of adults and more than four-fifths of adolescents do not meet recommended thresholds for exercise. This article outlines the magnitude of the global problem. It discusses terms such as physical activity, aerobic exercise, muscle strengthening exercise, weight-bearing exercise, sitting time, and sedentariness. It presents and explains current guidance on physical activity, averaged across a week, for adults as well as special populations, including adolescents, the elderly, and pregnant women. It notes that immediate, short-term, and long-term benefits of exercise have been identified in thousands of randomized controlled trials (RCTs) and cohort studies, and pooled in hundreds of meta-analyses, for a wide range of neuropsychiatric and medical conditions. It explains the strengths and limitations of the RCT and cohort study data as well as explains how some of the limitations can and have been addressed. It demonstrates how the Bradford Hill criteria can be applied to support the credibility of the research findings. It outlines immediate as well as long-term risks associated with exercise, as well as factors associated with these risks. In summary, the benefits of exercise outweigh the harms, especially when exercise is performed in moderation and within the individual's comfort zone. Although any physical activity is better than none, individuals should attempt to reach the currently recommended thresholds for exercise. There is little additional benefit associated with exceeding the guidance, and there may be immediate as well as long-term risks associated with overexercising. Finally, sitting time and sedentariness are constructs that are independent of physical activity; greater sitting time and greater sedentariness are both associated with poorer health outcomes and should therefore be discouraged at the same time that physical activity is encouraged.