The electrical impulses to the leg muscles for their action come from your back. Any disruption in these impulses may cause weakness to appear. Weakness in your legs may range from subtle weakness in rising up your toe or moving your ankle, to more severe cases with difficulty in walking. Sometimes this may occur due to pain instead of any compression over the nerves at your back. You may need some sort of assistive devices to help you in walking in cases of profound weakness. So it is advisable to consult your specialist immediately if you seem to have any of these leg weakness symptoms associated with your back pain.