Walking is not something that I do as a hobby or an extra exercise, walking is part of my daily routine... My job is all physical work. I stand up and walk for 9 hours per day and that's on top of my daily bike commuting and other forms of exercise which I do. I hardly ever sit down, and a lot of my life is spend either on a bike or standing/walking. I do take some rest on the weekends, but even on the weekends I still end up doing some physical activity. I think I am getting too much aerobic exercise, but at least it keeps me trim and in great shape.