this is more or less the message that Lou Schuler and Alwyn Cosgrove convey in the recently published book “The New Rules of Lifting for Abs” (Avery, 2010). A very interesting one if you’re looking for an entertaining reading.
Schuler, an award-winning fitness journalist and one of the authors of the book, confessed that he hasn’t done a single crunch in at least ten years "The idea of doing crunches and sit-ups is to make the abdominal muscles bigger," he told.
"But we all have muscles there. My son had a six-pack for most of his childhood, without doing a single sit-up. He was just a skinny, active kid."
We all know that diet is far more important than exercise if you want a six (or even eight) pack. Most guys also probably don't realize that the most effective moves for chiseling the belly aren't crunches or sit-ups (which can actually do more harm than good). In fact, the best exercise to target your gut does the exact opposite of a crunch, and that is a plank!
What’s the difference?
In a crunch, you bend your spine. In a plank, you brace it. That makes all the difference. Exercises that stiffen the abdominals generate greater forces in your hips, which allows you to move with more explosiveness and efficiency. They also make you look better.
Two studies from 2006 and 2008 show that moves like the rollout, work the upper and lower abs, and are about 25% more efficiently than a crunch or a sit-up. How's that for maximizing your gym time?
According to a study (published in the Journal of Orthopaedic & Sports Physical Therapy in May 2011) the Swiss ball rollout - in which you place your fists on a ball and extend your body like a bridge - is much better than the crunch for creating a ripped stomach and building strong lower-back muscles to support your spine.
The rollout isn't some newfangled exercise invented in a laboratory; it's simply a dynamic tweak of the plank, one of the oldest exercises in the book.
Planks are also safer
Thanks to Stuart M. McGill, Ph.D., an influential kinesiology researcher at the University of Waterloo in Ontario, we now know that crunches do a number on your spinal discs, which are parts of your body that do not heal. McGill measured the forces placed on the spine by sit-ups and crunches. He found that the compression created by a crunch is so high that if you knocked out a set on the job and the Occupational Safety and Health Administration was there to measure the load, your employer could be charged with violating workplace-safety laws. In other words, if you're looking for a herniated disc, look no further than the crunch.
The basic plank (toes and forearms on the floor, shoulder blades pulled and down, butt down, body straight) is harder than you might realize.
Once you can hold it for 60 to 90 seconds with ease, move on to a more challenging version of the classic. Do them in front of a mirror so that you can monitor your form, and be sure to break when it goes off.