The most common exercises seen in the gym involve various bending and curling motions of the abdominals. Crunches, side bends and sit-ups are the most popular examples. This trend has continued in spite of the fact that top fitness professionals - like Mike Boyle, strength and conditioning coach for the Boston University hockey team - have moved away from abdominal bending exercises in favor of ab stability techniques.
Stability exercises for the abdominals would include exercises like planks and half-chops. The chief purpose of the muscles of the midsection is to resist movement - in order to spare the spine the shearing and compressive forces that can lead to herniation. According to world-renowned back specialist Prof. Stuart McGill, The National Institute for Occupational Safety and Health set the action limit for low back compression at 3300 N for manual laborers. Repeated action at this compression level leads to a much higher rate of worker injury. A sit-up imposes between 3200-3400 N of compression on the spine.... every repetition.
According to Boyle, McGilll and others, movement should come from the hips and upper back, not the lower back or abs. Not that the midsection should be completely immobile: there must be some give and range of motion; but motion should not originate there.
When the various abdominal muscles are weak, they do less work. The over-active lower back muscles tend to take over, get overly tight - and then the pain sets in. Training the muscles on the sides and front of your core to resist movement will allow your lower back to do less work, and will also relieve your spine.
Have a knowledgeable trainer show you how to do front and side planks. Begin with a round-robin of 8 seconds on each side. Do two or three rounds a couple of times per week, until you feel comfortable and strong. Then add a couple of seconds to each side. And drop the bends and crunches!