I still haven't found a precise description of what the shoulder blades should do during the overhead press.
About the sagittal plane, should they be retracted (pinched together), neutral or protracted (and why)? The stronglift guide says that you don't have to squeeze the shoulder-blades, so it looks like they should be neutral. However, sometimes many people suggest me they must be absolutely retracted the whole time (for instance I've received this advice here). Where is the truth and which is its bio-mechanical reason?
About the vertical plane, should they be depressed, neutral or shrugged? Plenty of sources (Stronglift Guide, Pheasyque Sketches etc) say it is crucial and good to "shrug at the top" to create space in the AC Joint for the arm raising. My question is about if we have to shrug only at the top (so: depressed shoulder-blades the whole time and final shrug at the lockout) or gradually during the execution. And if such a shrug must be performed only by the upper trap or also by the serratus anterior.