The human species was designed for movement. Until the mid-19th century, humans lived as gatherers, scavengers, toolmakers, hunters, farmers and artisans. For 99.9% of human history, physical demands were typical of daily life and an expected part of the everyday world (Astrand, 1986). Our species not only survived but flourished for several thousand generations prior to the advent of the automobile, television, video games and the Internet. Within only a few generations, the physical activity demands of work, domestic chores and leisure time have decreased so dramatically as to be nearly non-existent in industrialized and urbanized environments.
However, it has also become increasingly clear that many of the chronic diseases we face today are associated fundamentally with the pervasive sedentariness of modern life. A case can be made that habitual physical activity has a biological basis with a central control, and that physical inactivity disturbs normal function and contributes to chronic energy imbalance (Rowland, 1998). This is not a plea to return to the physical toil that our ancestors endured. Rather, it is a reminder that that our bodies have an inherent need to be exercised. If our overall health and functioning are to be optimized, we need to be physically active on a regular basis