Nope. I ain't crunching. Cuz I wanna strengthen the muscles underneath, which are the transversus abdominus and the aponeurosis which it attaches to. It doesn't cross any joints, so all it does is tighten the aponeruosis (supporting your back and aligning lumbar spine to pelvis) and flatten your stomach. It also cues in the multifidi (along the spine) and the pelvic muscles which help stabilize to a lesser extent.

The "six pack" is rectus abdominus. That's the muscle that bends you forward into a crunch. That one isn't going to help your back, and in fact patients who only do crunches end up with pretty hefty back problems because rectus overwhelms the "core" muscles. If you think about it, walking around hunched forward (overdeveloped rectus) will give you quite a backache!

Obliques have two functions: they bend you forward and twist you, and they can also help transversus during extreme effort by locking down the entire abdomen. (think side planks) Again, you don't want to walk around all the time bent forward and/or twisted to one side, and if you lock down the abdomen all the time you won't be able to breathe deeply.

If you absolutely feel you MUST crunch, please do diagonal crunches. Better to do planks (prone and side) if you want stability, because then you are training your obliques to stabilize.

If your lower abs aren't strong enough to hold your belly flat, no amount of weight loss is gonna give you a flat gut. I've seen plenty of patients with almost no fat who pooched out because they lacked muscle tone. I even worked with a patient who'd had a tummy tuck, but looked quite fat because her muscles were on a slack all the time.

That one was a real challenge! Her skin was tight enough from the tummy tuck that she felt like she was holding it "in". Teaching her was difficult because the usual cues I use for folks just didn't work. (I eventually had to use a weighted ball and a lot of ingenuity!)