It's part of a muscle if you think you can activate individual heads by doing stupid shit then you are fucking dumb. Anybody that says they are doing "rear delts" are newbies in BB world. It's the same when people write out their meal plan: 1. meal one 10:am 1 cup of brown rice 2 cups broccoli etc I don't expect you to understand it. It's funny hearing you talk about the rear deltoid like that though. Do you believe you can activate the individual heads on the bicep and triceps as well? What about the quads? There are tons of muscle inserts that go into the humerus. The deltoid is one of them. Googling for 10 seconds to try to say something about the humerus isn't going to impress me. If you want to learn about the AI, I wrote exactly why it is used. Diuretics aren't used by BB and if you use them that means you are an idiot. You use any type of AI to get the last bit of water out of the body pre-contest. You still didn't say what you meant by "secondary mover" what is a primary mover? Keep going if you want.