Accumulating data from both human and animal research exists demonstrating positive health outcomes associated with physical activity across lifespans. It becomes clearer that physical activity plays a critical role in preventing a number of chronic diseases, such as cardiovascular disease, type 2 diabetes, obesity, osteoporosis, and cancer, as well as premature mortality. To date, unfortunately, only a small proportion of population in developed and/or developing countries is physically active enough to achieve the associated health benefits, placing physical inactivity (i.e., lack of physical activity) as one of the major public health concerns worldwide. Further, more recently, there is growing evidence concerning sedentary behavior, independent of physical inactivity, as an emerging health risk behavior in contemporary societies. Recent studies showed that not only the total volume of time spent being sedentary, but also the manner in which sedentary time is accumulated is associated with health outcomes. However, available data are limited and sometimes inconsistent, leaving a gap in understanding the role of sedentary behavior on health in various population groups.

As part of continuous efforts to extend our understanding of two of the most influencing lifestyle factors on human health, physical activity, and sedentary behaviors, this special issue focuses on a broad range of topics in epidemiological research on physical activity and sedentary behavior within a behavioral epidemiology framework. We invite investigators to submit original research articles as well as review articles addressing recent advances in epidemiological studies defining physical activity and/or sedentary behavior as either an exposure or an outcome variable. More specifically, this special issue is dedicated 1) to understand how physical activity and/or sedentary behavior independently and/or jointly influence the risk of developing adverse health outcomes and longevity in various population groups, 2) to explore the factors at various levels (e.g., individual, environmental) influencing physical activity and sedentary behavior , 3) to improve physical activity and sedentary behavior assessments in epidemiological research, and 4) to explore the evidence-based intervention strategies to modify the behaviors at various population groups. We encourage investigators to submit studies employing methodologies in epidemiology such as randomized controlled trials, community-based interventions, observational study designs, and systematic reviews. Potential topics covered in this special issue can be found below. Submitted manuscripts should not have been previously published, nor currently under review for publication elsewhere.

Potential topics include but are not limited to the following:

• Observational epidemiological studies describing the levels and/or trends of physical activity/sedentary behavior across populations with diverse geographic, race/ethnic, demographic, and socioeconomic backgrounds
• Prospective or cross-sectional epidemiological studies examining the independent or joint relationships of physical activity and/or sedentary behavior with chronic health conditions (e.g., cardiovascular and cerebrovascular diseases, diabetes, cancer, osteoporosis, and premature death) in diverse population groups
• Prospective or cross-sectional epidemiological studies examining the influences of physical activity and/or sedentary behavior on healthy growth and development of children and youth
• Experimental epidemiological studies examining the effects of interventions to promote physical activity and/or reduce sedentary behavior in diverse populations (e.g., children and youth, patients, pregnant women, and older adults)
• Methodological studies examining the validity and/or reliability of physical activity and sedentary behavior assessment methods
• Ecological studies examining social and environmental determinants or correlates of physical activity and/or sedentary behavior in diverse population groups