The back, neck and shoulders can suffer if a static position is held for a long time. If you have to spend hours at the desk, protect your back by moving, stretching and changing position as frequently as possible - set an alarm if necessary to remind you.
The following sequence of stretches can be done at the desk, moves the spine in all directions and mobilises the neck and shoulders. It can be done all in one go, or spread through the day, one stretch/movement at a time. Every minute spent moving or stretching will help to keep your back happy.