What is a reverse crunch? Reverse crunch is where you are lying down on a floor and instead of doing a crunch with the upper body what you do is you lift your butt up off the ground so it reversing the motion.
Reverse crunch is where you are lying down on a floor and instead of doing a crunch with the upper body what you do is you lift your butt up off the ground so it reversing the motion. That would engage the lower ab more than the upper abs. But another thing to keep in mind is that when you contract one muscle in the musculature rectus abdominus you contract the other and you really can't separate the two. Even if somebody wanted to do crunches they will still strengthening the lower ab musculature.
But all of the ab exercises on the ball will work the whole ab musculature. Not just only the rectus abdominus but also the internal, external obliques and the transverse abdominus which is a deep stabilizing muscle of the core. It works the whole system much more complete than doing crunches. One of the problems with crunches in working rectus abdominus ironically is that it's not teaching core stability because of the way it's supposed to work when the body needs to stabilize the core. It first needs to fire the intrinsics muscle that would be the transverse abdominus, multifidus and then internal external obliques. Let's say someone does 150 crunches a day for four or fives days a week. What they are doing is retraining the nervous system. So when people do a lot of crunches what they are doing is re-teaching the system to work backwards.
It's better to teach the core to work in a stabilizing sense. So once again that doesn't mean not to do crunches but it does mean to do a whole lot less crunches and to work on the more routine for the core.
