1) people stopped walking as much- to church, to school, to work, to the playground, etc. and started driving more, including longer commute times.
2) People came in off their porches, particularly in the South where I live where the front porch was the center of social activity, and began to watch TV in the evening instead of interacting with neighbors.
The combination of these two things contributes to isolated, stressful, and inactive lives.
In "Keeping the Faith: Ordinary People, Extraordinary Lives", a notable book by Dr. Wayne Flynt (renowned history professor from my Alma mater Auburn University) this regretable mass exodus in the 1950s and 60s off the porch and into the living room is written about in great detail.
Walking is not something most Americans do on a regular basis, unless you count walking from your car to the shopping mall, but it's the best form of exercise.
It's free, it helps build your sense of community because you meet and interact with people, it relieves stress by allowing you to free your mind, and it's interesting.
I even suggest you become a flaneur. Flaneur according to wikipedia: one who strolls, the man of leisure, the idler, the urban explorer, and the connoisseur of the street.
I'll see you on the street.