Sitting at a desk all day long can lead to rounded shoulders and poor posture. This hunched posture, creates a limitation in movement of the thoracic spine. Improving mobility in the thoracic spine will not only improve your posture but will help with shoulder movements.
The video below will show you how to do a thoracic spine mobilization with a foam roller.
Lie on your back with knees bent and your glutes and feet on the floor. Place a round foam roller under your upper back and clasp your hands behind your head to support you as you do this exercise. Pull your elbows close together and let your head drop to the floor. Try to wrap yourself around the foam roller extending the thoracic spine as far as you can go comfortably. Bring your upper body up to the starting position and perform 3 to 5 repetitions, Reposition the foam roller an inch or two higher or lower and perform another 3 to 5 repetitions. Be certain to keep the foam roller off your neck and lower back.