This is an excerpt from Introduction to Exercise Science With HKPropel Access by Duane V. Knudson.
By Duck-chul Lee
Physical activity and exercise play key roles in physical, mental, and social health; help prevent, delay, and treat chronic diseases (e.g., cardiovascular disease, diabetes, obesity); and contribute to healthy aging and longevity throughout the life span. How do we know this? Physical activity epidemiologists have been trying to find the answers to the following common questions about physical activity and health: “Who is active?” “Do active people get sick less often and live longer?” “What is the minimum and optimum amount and kind of physical activity for maximum health benefits?” and “How can we promote physical activity at the population level?” To investigate these important topics and produce evidence-based scientific data and knowledge, physical activity epidemiologists conduct large human research studies using various epidemiological research methods and statistical analyses. They also systematically collect data and contribute to developing physical activity recommendations in various populations for disease prevention and health promotion. Most exercise science professionals help their clients and the family and friends of that client, but physical activity epidemiologists in exercise science positively influence the health and longevity of whole populations of people throughout the world.
Epidemiology is “the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems” (Last, 1988, p. 141). A recent branch of epidemiology aligned with kinesiology and exercise science is called physical activity epidemiology. In a foundational study Caspersen described physical activity epidemiology as a two-part field:
- First, as a science, “it studies the association of physical activity, as a health-related behavior, with disease and other health outcomes; the distribution and the determinants of physical activity behavior(s); and the interrelationship of physical activity with other behaviors.”
- Second, as a practice, “it applies that knowledge to the prevention and control of disease and the promotion of health.” (Caspersen, 1989, p. 425)
Based on these descriptions and concepts, Lee and Brellenthin concisely defined physical activity epidemiology as “the study of the distribution and determinants of physical activity, its associations with health-related outcomes, and the application of this study to disease prevention and health promotion” (Lee & Brellenthin, 2023, p. 324).
Physical activity and exercise can be either an exposure (independent variable) or outcome (dependent variable) depending on the study design and purpose of a study. When studying the associations of physical activity with disease and other health outcomes, physical activity is considered an exposure. When studying the determinants of physical activity, physical activity is an outcome. However, the associations of physical activity with various health-related outcomes (e.g., heart attack, cancer, mortality) are the central part of physical activity epidemiology. Findings from these health-related studies provide important data to develop effective public health strategies and policies. From both clinical and public health perspectives, physical activity epidemiology is an important growing area of science and practice for the prevention of disease and health promotion.
What Do Physical Activity Epidemiologists Do?
Epidemiology is a cornerstone of public health, which promotes and protects the health of people and provides the scientific backbone to quantify health problems; identifies and monitors disease risk factors; designs and conducts human research projects; measures the strength of the associations between risk factors and health outcomes; and produces evidence-based data.
Although epidemiology is a longstanding central component of public health research, physical activity epidemiology was not born from public health; rather, it established its own research area. Researchers in medicine and kinesiology (e.g., Drs. Morris, Paffenbarger, and Blair) who were interested in physical activity, fitness, and health adopted epidemiological research methods (e.g., prospective cohort study) and established the new field of physical activity epidemiology over the last half century (see History of Physical Activity Epidemiology section below). Physical activity epidemiology recently contributed to expanding the scope of public health by adding physical activity as a relatively new and powerful lifestyle risk factor in addition to the traditional risk factors such as diet, smoking, and alcohol abuse. Physical activity epidemiology is also a growing subdiscipline of exercise science because of increasing emphasis on improving health of the general population and not just performance in sport. Physical activity epidemiologists actively collaborate with investigators from various related disciplines including exercise physiologists, sports medicine doctors, cardiac rehabilitation specialists, other epidemiologists (e.g., in diet, cancer, cardiovascular disease), public health scientists and practitioners, psychologists, physicians, transportation engineers and city planners, policy makers, and community advocates.
Most physical activity epidemiologists have a doctoral degree in kinesiology, epidemiology, or medicine. In addition, most physical activity epidemiologists have completed a postdoctoral research fellowship after their doctoral studies. It is common that physical activity epidemiologists have different backgrounds for their doctoral program (e.g., exercise physiology, exercise psychology, physical activity measurement, or epidemiology from public health). They then develop skills, experience, and knowledge of physical activity epidemiology (e.g., how to conduct epidemiological research, analyze large cohort data, and design and execute clinical trials) during their postdoctoral training on a specific research topic such as cardiovascular disease, cancer, diabetes, or obesity.
Although primary interests are different between physical activity epidemiologists, they all have physical activity at the center of their research, which is one of the key behavior components of chronic disease prevention from a public health perspective, in addition to diet, cigarette smoking, drug and alcohol use, and sleep. One example of the relationship between physical activity epidemiology and public health is Healthy People 2030, which was first developed by the USDHHS in 1979 and is updated every 10 years (USDHHS, 2020). Healthy People 2030 sets data-driven national objectives to improve health and includes physical activity objectives for 2030 focusing on reducing inactivity and increasing physical activity to levels recommended in the U.S. Physical Activity Guidelines.
As scientists, physical activity epidemiologists investigate the distribution and determinants of physical activity and its associations with health-related outcomes. For example, they look around at the various environmental factors from natural environment to individual determinants that influence physical activity such as weather, air, parks, transportation, culture, income, gender, age, and beliefs. They also study how much risk of developing chronic diseases (e.g., cardiovascular disease) could be prevented by being physically active and fit in various populations (e.g., individuals with overweight or obesity). As practitioners, they work to prevent and control the disease by promoting physical activity in populations. Thus, physical activity epidemiology is considered a habilitative or preventive science rather than laboratory or rehabilitative science. As public health workers, physical activity epidemiologists not only conduct physical activity and health research, but also produce important scientific data to develop and enhance national physical activity guidelines and plans for public health policy makers, health professionals, and individuals.
Physical activity is one of the key behavior components of chronic disease prevention from a public health perspective, in addition to diet, cigarette smoking, drug and alcohol use, and sleep.