I don’t think it matters a lot, but I guess the way I do it is somewhere in between? I get relatively close to the end of the movement before I start to rotate, but it’s not as if it’s two distinct, separate movements. It’s also not completely fluid throughout the movement. I think the end contraction is really the most important part, and the full range of motion. How you get there shouldn’t matter much.
EDIT: I should also add, I know in the past I’ve generally advocated for fast-as-possible contractions. I don’t do that on this movement, it’s very much under control.
