I was watching standup of the comedian Bryan Callen on YouTube and his set was about how he always wanted to be a hero. He described what heroes are like and one of the aspects of them was the fact that all heroes have very muscular backs. He was making jokes by giving reasons that account for this fact. One of them was the fact that they are saving children by "pulling them out of wells all day". He mimicked a movement of someone reaching down and pulling something up as if he was taking a child out of a well and said:
"This movement right there, gets your back"
What does "get" mean in this context?
I'm supposed to provide some research but no definition really fits for this context even though there is a plethora of them for this word. The only thing I suspect this could be is that this really is a shortening of "this movement really gets your muscles big". The rest of the sentence is implied here. Plz, help guys.