This is one of my favorite ways of reducing pain and staying fit. Apparently it's called "microworkouts"... I try to add several short 3 minute workouts throughout the day to get my blood circulating and keep my muscles happy. If you want some professional instruction and a private trainer right there with you by your desk, you can register for a free subscription to breakpal, where this woman pops up on your screen and brings you through an exercise program (kind of like Harry).
Or just improvise! Very many catchy tunes last around 3 minutes, so crank up the volume and dance, squat or do your favorite aerobic disco moves for as long as the song lasts. If you manage to get your blood pumping it is guaranteed to release endorphins and reduce muscle pain.