Every day, your spine gets compressed with the natural forces of gravity. Under normal circumstances throughout the day, you sit, stand, then sit again changing the angles and amount of compression that is forced onto the lumbar.
However, if you stand for a long period of time (say for several hours at work) the amount of compression that is forced on the lumbar is extreme and can cause excessive force on the lumbar. This can cause the spine to either to have too much curve (a condition called Lordosis) or have too much force placed on the discs. can cause additional pain and exacerbate the problem.