Sitting for hours is bad ok...
For a long time I was a smoker, I would often walk out of the building with others, and take a break. Talking about their or my problem of the minute.
One of the other engineers who DIDNT smoke started coming out with us when we went. After a few weeks he noted out loud how his productivity had been UP since he started taking the journey with us.
It seems counter intuitive that getting up and moving around (even to do something bad) is good for you.
If your not a smoker, go hang out with them a few times a day (or use their smoke breaks to take your own break away from your desk).