So much of writing is sitting, sitting, sitting. But it doesn't have to be that way. No, it really doesn't.
I, perhaps like many of you, am a very stubborn person. When I start on something (creative writing, work writing, any project) I get very focused. I don't want to give it up until the project is done. This can be a great quality, and it can be very hard on the body.
Add into that all the time that a person can spend at a computer all day (work, business, administration, whatever) and it all adds up to a lot of sitting.
Give yourself permission to get up and move. You really will feel better. You'll think better, too. The body and the mind inform each other. Don't ignore your body. Let it inform you. Everything will feel better.
Ask yourself — do we want to end up like the humans in WALL-E? (Kidding, sort of, but the movie is marvelous social commentary. If you haven't seen it, view it. It's well well worth it!)
Remember to move — whatever that means for you! (Hint: remembering to breathe while you're sitting is a really good idea, too. Try it. You may be surprised to learn that you are holding your breath.)