What kind of contortion would change the location of the center of mass?

You can't change the motion of the center of mass, but by keeping the center of mass outside the body, you could theoretically miss the board (even though your center of mass would go through it). As I said, that's the way expert pole vaulters do it. Their center of mass goes below the bar (so if the board were from the bar to the ground, it would be similar to what you've asked), but every part of their body passes over the bar. What you've asked would be much harder because a pole vaulter works at the slowest point of their path and they use the space under the bar in their contortions. The way to miss the board is, for example, to fall belly first and horizontally at the board, then, just before impact, flip your upper body, head, and arms, around under the board, and then before your legs hit, flip them around too. Another way to do it (or at least think about it) is to make your body into a rotating U, then time the rotation so that the U is pointing down when you reach the ...  more