Part of the difficulty in investigating the epidemiology of physical activity has been the lack of a framework to examine the relationship of physical activity to heart disease and health. In the current report, an overview of the spectrum of physical activity is presented to provide a basis for understanding the epidemiology of activity, cardiovascular disease, and health as well as a discussion of major methodological issues associated with investigating the activity spectrum. First, it is necessary to examine what is meant by physical activity and fitness.
Physical activity is a concept that is well known, yet it is difficult to explain.
Typically, epidemic logic studies have not defined activity. Instead, the researchers assumed that physical activity was what the assessment tools were measuring. Other approaches have used a restricted definition of physical activity by examining the amount of time in vigorous activity. Active individuals have also been defined as individuals with an increased rate of body movement. It is interesting that in the more than 50 articles on activity and heart attack, at least 25 different measuring tools and, therefore, definitions of activity have been employed.