Alright now I'm thinking and here's what I've got:
Right now we're talking long, full body swing right? I was NOT talking about tuck and shoot, I was talking about what we consider a full swing, but it is still not full body, because it bends at the waist/hips. This is what I assumed we were supposed to get out of this; that a longer, completely straight body swing is better because it puts more energy into the pole. However, I was going to say that it is necessary to keep the hips loose and be able to bend at the hips during this swing, instead of swinging with the whole body straight. The entire body swing would put in a lot of energy, but it would also be very slow, and I dont think that the vaulter would be able to catch the ride in time. Aside from this, moving from
http://putfile.com/pic.php?pic=7/18723103144.jpg&s=f10
to
http://putfile.com/pic.php?pic=7/18723114073.jpg&s=f10
with a completely straight body (no pike at the hips) would take a lot more energy, thus wasting the additional energy that would be gained by a full body swing.
BTW Bethel, Agapit asks if the swing should be shortened by bending at the HIPS, which is what I believe most people will do during what I consider a swing and not a tuck and shoot. Note the bend at Bubka's hips, while he is doing the swing. I'm pretty sure you'll agree that bubka was not a tuck and shoot vaulter during his career.
http://putfile.com/pic.php?pic=7/18723214841.jpg&s=f10