Lee Boyce has been going on and on (in several Tnation articles) that in order to do a pull up/chin up properly you need to FIRST retract and depress your shoulder blades whilst in the dead hang before pulling yourself up.
He says that this is the way to properly engage the back in the movement (instead of 'arming it'), and you should be humbled by how little weight you're able to use when doing this strict form.
However, why would being able to use your back properly result in being able to use less weight? Your back is a bigger and stronger muscle group than your arms, so if you're able to engage your back properly, shouldn't you be able to use more weight, not less?
Basically, all these years, I've been trying to retract and depress my shoulder blades at the same time as pulling myself up (I like to try to let the shoulder blades move naturally as the arms move instead of separating the movements out like Lee Boyce indicates you should do). Does that mean I've been doing it wrong?
Lee Boyce also says that if you're doing chin ups properly you should get sore deep in the mid-back (almost lumbar back). I get sore around the arm-pit area moving across to the lower shoulder blades.