Ideally this exercise should be done on the floor, with you on your hands and knees. But since you probably can't even see your floor for all the tax return folders, this variation allows you to stay off the floor but still get some stretching in your lower back.
Step 1: Stand up from your desk chair and take two steps back from your desk.
Step 2: Separate your legs so they are shoulder-width apart.
Step 3: Lean forward and place your hands on your desk, palms down, arms straight, and keep your back straight.
Step 4: Pull in your stomach muscles, arch your spine, lower back, shoulders, neck, and let your head drop.
Step 5: Hold for 15 seconds.
Repeat 20 times.
See the complete library of Workplace Fitness exercises.