Previously I showed an exercise called abdominal hollowing, which as I explained is essential for strengthening the abdominal core. A strong core leads to stabilization of the low back through a tightening of the musculature surrounding the area, as well as through the tightening of the thoracolumbar fascia.
Another exercise to help strengthen the abdominal core, as well as assist in stretching the hip flexors, is called pelvic tilting. A pelvic tilt is bringing the pubic bone and belly button closer together. It essentially engages the psoas major muscles to either pull them out of the equation as a contributor to abdominal crunches, OR to get a better psoas stretch during the hip flexor lunge or runners stretch.
Watch the video below to get a handle on pelvic tilting.