OK. This is turning into an Abs tutorial. The abs, rectus abdominis is one muscle, but two set of nerves, an upper, and a lower set. Some people think that doesn't make a difference. They're totally wrong. If you make a top down exercise movement, then the upper nerves trigger the RA. If you make a bottom up movement, the lower nerves trigger the RA. Whichever set of nerves triggers the movement, the bottom or top, indicates which part of the RA gets worked the hardest, and the other part just goes along for the ride. Hint: the lower nerves get triggered the least. Note: hanging upside down, will trigger the lower nerves first. Guys, such as Sandow, and Grimek, would exercise their abs in a hanging upside down position.