Over the last twenty plus year in this industry I have seen more magazine covers and now internet headlines than I can count (now my clients will say that’s not hard to do!) touting something about a tight core or six-pack abs. The truth (and problem) is many are heavily focused on crunches and crunch variations. Crunches done in large numbers can be bad for the lumbar spine (low back); there are only so many flexion (crunch action) movements our back can take before there is a structural breakdown. Disk herniation is a common result from this breakdown. Dr Stuart McGill uses a video in his lectures of a dissected rat spine that is put through large numbers of crunch movements until the spine breaks down and disk herniations occur.
Better options for a healthy core:
Plank varieties (regular, single leg, single arm, opposite arm/leg, side, etc.); these can be performed for time or breaths. It is not about the length of time, think quality of position. If you are doing a two minute plank, but only have the ability to hold proper position for thirty seconds, then you will have spent one-minute thirty training the body in a bad position.
Rotations/Anti-rotations (chopping, diagonal lifting and pallof pressing performed in the following positions: kneeling, ½ kneeling, lunging or standing); biggest key is to keep the low back stable (do not twist or rotate through this area).
Carries (farmers walk, suitcase carries, front rack, overhead); this is a great way to work the core and grip strength. Maintain good posture, do not lean to one side, forward or back (over extension).
Low Back (hip hinge work using the following actions; extensions, reverse extensions, deadlifts); movements are done bending (hinging) at the hip not by bending at the lumbar spine (low back).
For a complete core pick one movement from each type of action one to two times per week.