Low back pain from sitting is due to mechanical stress on the body. When the body isn't well-aligned, your posture and therefore, balance, is weak. When you stand up with weak posture, the simple act of balancing will overwork some muscles and cause stress on joints. The key to reducing this strain is to
improve balance, the ability to control how you balance, and to retrain muscles and nerves for less pain and better function.
The first step towards stronger posture is improving the symmetry of how your body moves on each side. In fact, just changing the position from which you move can help free up locked and stiff joints, resulting in stronger posture and less pain.
A good stretch, The Sitting Leg Cross Stretch, is an easy back and hip stretch you can do at your desk. You can use your office chair or, if you want to challenge yourself, do the stretch while sitting on an exercise ball.
How to perform the Sitting Leg Cross Stretch:
Sit tall and strong on the front edge of a chair or ball, and cross your left leg over the right knee. Pull your belly in to brace your core. As you breathe out, keep your head and shoulders aligned as you pull your body forward. Take 2-3 breaths, and come up with your posture still strong. Repeat on the other side.