I hate to suggest this (well, maybe I don't), but I don't see a pure straight-body vault when I see this film of Warmerdam. If he was the best of the best stiff pole vaulters, then where's the straight-body swing?
He does do a two-legged swing, but after that, he bends at the hips and at the knees - to varying degrees in various jumps. This is contrary to what Launder suggests he does in Chapter 5 of BTB2. On page 23, where he states:
BTB2 wrote:
... while the stiff pole vaulter did break at the hips to speed up the rotation of the body about the hands, they did not flex markedly at the knees or go into a tight tuck.
Maybe "markedly" is the key word here, but I could quote several other sentences in that chapter that also infer that stiff pole vaulters swing to an invert in a straight-body motion. And I think that Agapit also mentioned that in his Pole Vault Manifesto thread. Not so, from what the film shows us. And Figure 5.7 on page 23 (probably traced from film) show his hips and knees bent too, and his legs flailing awkwardly over the bar.
I think that all altius was trying to get at was that in stiff poling there is a long swing to cover the pole, that it was NOT just a jump and then ride on the pole (especially in a tight tuck/ball). I don't think that he meant that the best stiff polers swung to cover the pole with an ENTIRELY straight body, or even with just a little bend in the hips. Try to swing like that from just running up to a high bar. It's basically impossible (even with the fabulous 'jump-split'
).