Well-defined abs are common in bodybuilding, but few people actually have a tight, "vacuumed waist" – one that doesn't just look like a thick wall of bricks. Fortunately, there's one movement that develops this look more than any other.
The Pulldown Crunch
Seat yourself in a pulldown machine and grab the bar overhead as if you were going to do pulldowns.
Inhale very deeply and suck in your stomach as hard as you can. Try to push your abs against your spine.
Next, blow all your air out as you crunch down. Contract hard and really try to "cramp" your abs. Hold that bottom position for a beat or two and squeeze. It's a small movement, but do it right and your abs will be on fire.
Do sets of 10 to 12 reps as often as you like.
These are excellent for gaining control of your abs and for those who suffer from abdominal distention.