I'm a little stuck here. My goal is to draw a samurai leaping with his katana above his head, about to bring it down on his opponent, but I'm not sure where to start.

What I need to know, specifically, is the shape of his spine and the position his legs would be in.

Also, I'm used to drawing the head first, because I don't draw action poses very often, and it's usually easier to attach a body to head than a head to a body. I'm not sure if that'd be a valid tactic here though, because of what he's doing. Can someone give any advice on this?

Thanks in advance.

Oh, and if it helps, he's descending from his jump, coming down, not ascending.