Day 23: Cobra stretch
Traditionally a yoga exercise done on the floor, this Cobra Stretch has been adapted for the office. The exercise is designed to improve the flexibility of the abdominal and psoas  muscles as well as increase mobility in the low back. When doing this exercise, be sure that your chair is pushed up against a wall so that it doesn't move away from you.
Step 1: Stand, facing your chair, with your feet shoulder-width apart and about 24" to 36" away from the edge of your chair.
Step 2: Lean forward and grip the center of your chair's armrests.
Step 3: Keeping your arms and legs straight, allow your pelvis to drop toward the seat of your chair while you lift your chin toward the ceiling.
Try to hold this position for 30-45 seconds.
You can adjust the intensity of the stretch by how far you place your feet from your chair. The further away your feet are, the more intense the stretch will be on your abdominal muscles.
Reprinted from Deskercise! The Workplace Workout , by Dr. Todd M. Berntson