http://livefitbootcamp.com/bootcamp-fitness-blog/health-nutrition-santa-rosa/common-exercise-injuries-and-how-to-deal-with-them/
Common Exercise Injuries and How to Manage Them
If you workout, it is inescapable that injuries will occur. While you are able to do your best to avert them, they will still happen from time to time. When you work hard your body is pushed to the limits, so when fatigue sets in, it's more susceptible to harm. One of the most important things to remember during intense exercise is KIND. Our bodies can do some crazy and amazing things but that can work against us sometimes.
Ordinarily, when you start to feel pain in your lower back during center exercises, it's likely as a result of fact your abs are not in good enough shape to do the motion, or the muscles are too tired to maintain the exercise pattern. It's quite important to understand the body and to recognize the difference between a challenging exercise and a painful/harmful exercise. There are two types of soreness: the pain where you are actually hurting your-self and the painfulness where it "hurts so good." It's a superb line, but its there!