Step 1: Sit on the edge of the chair seat and lean back until your upper back touches the back of the chair.
Step 2: Tuck your tailbone under, and hold onto the arms of the chair for support.
Step 3: Bring your knees up – with your shins parallel to the floor – so that your torso and thighs make an "open suitcase."
Step 4: Close the "suitcase" by bringing your chest and knees toward one another.
Step 5: Open and close for 10 to 20 repetitions.
Step 6: Do 2 to 3 sets.
Put together your own office fitness routine by reviewing the exercises in our Workplace Fitness Library.
Source: Discover Fit & Health