I've searched for a topic like this but couldn't find one.

Whenever I'm doing exercises that are supposed to be working the back like 1 arm dumbbell rows or pull ups, I only feel stress on my biceps and not my back. I've read that when doing pull ups, you're supposed to try to imagine your elbow is lifting you up but I'm not really understanding what that means. I know when doing these, you're also supposed to feel it in your biceps as well as your back but I only feel it in the biceps.

Any strategies you guys know of that help you isolate the back area when doing these exercises?