The 3 positions in this stretch really loosen up your hip flexors and let your hips get back to their natural alignment, check out this post for the full details: http://woldfitness.com/2011/07/one-exercise-to-end-lower-belly-pooch/
If you're using this to help relieve back pain, check out these other tips: http://woldfitness.com/2011/02/17-ways-to-fix-back-pain-bootcamp/