Crunches and traditional sit-ups are bad. Everyone knows that. They will turn you into a hunchback.
Combined with texting and sitting all day at computers we naturally incline forwards at the waist and roll our shoulders forward, creating this hunched position. Sit-ups reinforce this position and put a massive load of pressure on the lumbar spine.
So why do people and institutions insist on doing them? Lack of education? Old habits die hard? Put up or shut up? Almost every BJJ & MMA club i have ever been do does them as part of the warm up.
Plus I still see those have-a-go-heroes at the gym performing them all the time with beads of sweat and a Ramboesque one-last-rep look on their hardened faces.
Say what you want about science and some of it's dubious claims no one can argue about sit-ups. It just plain makes sense. Look at the picture above of the guy on the laptop. That's the position your spine takes each time you crunch.
You need something else in your routine arsenal that will fire up the abs and tone your obliques. You need a crunchless core.
6 Pack Myths
You cannot get a 6 pack or 8 pack even by doing a ridiculous amount of crunches, sit ups, or some other exercise. Being able to see your abs is a result of exercise selection, and being in a caloric deficit phase.
That's why bodybuilders don't mind ballooning up off-season as they know once they are putting in the calories and exercise regime, once they restrict calories coming up to competition time their abs will start to show.
Don't believe me? See this famous pic of Lee Priest off season and then competition prepped.
The key is a reduction in bodyfat. If you work your abs 60 mins a day every day for a month your abs will not noticeably pop until you have got your bodyfat down to 10-12% for males and 16-19% for females. Naturally the lower it goes the more defined your abdominals will be.
You of course have to develop the muscles before the abs will show. Diet and nutrition is then key for how defined they will appear. I like to think of my abs as a work in progress. Currently I am not looking to put much more muscle mass.
I like my current weight as it keeps me nimble for bjj/mma training and I feel "fit" at my current weight of 77k. Previously I was 83k and I really had to work to maintain this weight. Before I started training I was 57K. Steroid free gaining natural muscle has been a great accomplishment to me.
When I am not watching my diet to strictly my abs will slide a bit. But I'm fine with this, not obsessive. As I know once i reign in the calories and junk food my abs will become more defined. I have naturally big transverse abdominals (front and side abs) due to genetics and working them smartly.
The Abs Are Not Just One Muscle Group
Another reason crunch movements are not great ab developers is that the abs are not just one muscle group. You do not have just the front wall that everyone sees in a classic 6 pack photo. You also have obliques running down the side of your body, from just below the rib cage to your hip.
Train Your Abs For Stability & Not Just Appearance
The abs act just like a girdle in times of old, and even today as many women like to wear them to retain shape or postpartum, and men with a little too much in the midsection (remember Riggs & company giving Murtagh dogs abuse about wearing one in Lethal Weapon?).
They stabilize the pelvis keeping you taut protecting you from the g forces of physical activity and everyday bending, twisting movements. No wonder you are taught to brace your abs when squatting. Strong abs are like a protective belt that can prevent you from injury.
You need an exercise selection that addresses the entire abdominal range to not only get those abs, but to protect you from injuries. Many people with really good visual abs have the misconception that their core is strong. Unless they have trained all of their abdominal muscles their can be an imbalance which can find you out some day on a heavy squat, or even when you twist suddenly.
Then there is a really cool muscle called the serratus, that bodybuilder look amazing when it shows.
Arnold is miles ahead of me on this one