Abstract
The 20th century in the United States has experienced a dramatic increase in life expectancy among adult men and women, an increase unprecedented in the history of this country. As a result, the pattern of disease and conditions most responsible for death in the United States shifted during the past century from infectious diseases and unintentional injuries to the current array of the leading causes of mortality dominated by the chronic diseases. During this same period, daily lifestyle dramatically shifted from a life full of active living to one of inactivity. The argument has been made that in the case of human beings, there has been little or no change in our genotype within the past 50 years. However, there have been major changes documented in the living environment among economically developed societies during this same time period. Through the collection of epidemiologic, clinical, and experimental findings, evidence suggests that physical inactivity is associated with the onset of chronic diseases of our day. Trends in physical inactivity, evident through the monitoring of transport, recreation, sport, and purposeful activity, have demonstrated that the current lifestyle of the 21st century has contributed substantially to the chronic disease burden in the United States and elsewhere. By addressing the domains that influence physical activity behaviors including the environment (both physical and social/cultural), health systems access, and behavioral correlates of physical activity and inactivity, the current chronic disease crisis potentially can be addressed.