Step 1: Sit on your desk with your knees over the edge.
Step 2: Lean back to a 45-degree angle, or as far as you can while maintaining a neutral spine (no arch). Proper technique is essential in this exercise. If you can get to that 45-degree angle without arching your back, great; if not, don't. The moment your back begins to arch, you need to come forward to a point where you can hold the angle.
Step 3: Rotate your torso and touch the desk beside your right hip with both hands.
Step 4: Repeat to the left.
Step 5: Do 8-10 repetitions to each side.
Put together your own office fitness routine by reviewing the exercises in our Workplace Fitness Library.
Source: Discovery Fit and Health