Most people don't think to train their lower backs. If you are working your abs, you should also be working your lower back. If your abs become stronger that your lower back, it could cause problems.

If you do have lower back problems or to prevent problems, here are a couple exercises that will help you strengthen those muscles.

* Plank - This can be done on elbows or on hands (like in push up position)
http://youtube.com/watch?v=ftA7H-VM4fc
*Superman
http://youtube.com/watch?v=8szJuzPt-sg
*Bird Dog
http://www.acefitness.org/getfit/exercise_display.aspx?pageID=687&Catego...