 One of the heads of the bicep attaches over the shoulder. When you lift your arm up above your head, the biceps in a shortened position. And so then you curl from there and you get this really gnarly squeeze. If you've never done it before, try it and you'll see what I'm talking about. Now on the opposite end, you want to talk about the stretch position, attach a band behind you, walk away from it, allow your bicep to stretch and then curl from there. That, that one's gnarly. That, that makes things hurt.