There is a lot of articles out there on how to build core strength to prevent back pain. For me the vast majority needs to be working on core stabilization vs just strength. I have seen a ton of guys at the gym that do massive amounts of situps and crunches but still complain about back pain.
The problem is 3-fold.
- The core is made up of a lot more than just the 6-pack (rectus abdominus). There is the obliques and transverse ab muscles, the low back extenders (QL and paraspinals) and the gluteal muscles. They are addressing only 1.
- They are working the muscle primarily for strength when shortening the muscle (concentric) while most low back injury prevention needs lengthening control and strength (eccentric contractions).
- The are seeing how much the muscle can move rather than how much stress on the muscle can you have without moving the spine out of optimal position.
Planks are a great exercise. Side planks will get the sides of the abs as well. I do like ball knee tucks. Because you are further from the 2 points of contact, you get good eccentric work bringing the knees back. You are directly in a plank position and can work that in with the workout.
Finally, Single leg dead lifts are a great exercise. Please make sure to hip hinge and see the previous post on it.