I think that picture is taken from this book:
http://www.amazon.co.uk/exec/obidos/...roduct-details
I bought it a few years ago - the one in the link is the new edition. It's a wicked read and ref. book. It breaks down all the excercises for BB'ing and when it shows the pictures of the movement it shows it in see-through so you can see exactly which muscles are working. It even breaks it down in to primary and secondary involvment. Defo worth the £12 !