You're quite right, I read "not just for beginners" as "just not for
beginners".

And you've correctly identified that I am a little worried about this
sort of thing, since I read an article about preventing shoulder
injuries, where the author said this rolling up off the bottom is one
way to dislocate a shoulder. He said he would write another article
about how to prevent that, but it hasn't appeared yet. I really really
don't want to dislocate a shoulder.

Bernie