Most jobs require us to sit for prolonged periods of time. The sitting position causes a shortening of muscles along the front of the body (anterior aspect). To compensate, the back side of the body (posterior aspect) must elongate to allow for this shortening. This leads to muscular imbalance that can cause not only back pain, but pain in our limbs.
To undo this imbalance, the body must do the opposite: extension. One of the best exercises is seen below, but ideally you would avoid the issue by alternating between sitting and standing.