So how do you know if you're helping yourself or hurting yourself when you feel something while you're exercising?
There is a really easy rule of thumb...
If the pain is in a joint and you feel it while you're doing the motion, that is an absolute no go. You should not feel anything in any joint when you're doing an exercise, no stiffness, achiness, twingy kind of anything.
If you feel muscle fatigue, like you're going through the motion and it just feels like you can't do another repetition because the muscle has gotten really tired. That is awesome.