Me: Your elbows need to be under the bar. Keep the chest out and drive the elbows forward as you rise out of the hole.
Internet Acquaintance: Under the bar? I thought the cue was elbows up! isn't elbows under the bar referring to a High-bar squat?
Me: I can only guess what you mean by "elbows back and up", and if you're like most people who I've seen doing this (and like the pic above), you are cranking the elbows skyward behind you, internally rotating the crap out of your shoulders, and making it a lot harder to maintain proper thoracic spine extension. If so, watch my video again, then reread Rip's chapter on the squat, paying closer attention to elbow positioning in the pictures.
I get this a lot. The problem is that these people get stuck on Coach Rippetoe's phraseology of "lift the elbows", which is NOT the same thing as internal rotation. People relatively new to the squat think that raising the elbows skyward is a good idea, because it creates a larger shelf for the bar to sit on. Unfortunately, this just encourages poor bar positioning in general and, in addition to setting yourself up to dump the bar over your head, leaves the bar fully supported by the arms and rear delt strength instead of the skeleton (where it should be). We are NOT trying to hold the bar up with the arms (See Wrist Pain When Squatting for more on bar positioning).
Thoracic extension is what we want and that is the purpose of driving the elbows forward. The shoulders do not rise like a shrug ("the ears are shoulder poison" - Jeff O'Connor). The upper back contracts like a rear double biceps pose or bent-over laterals, and the arms are simultaneously wedging the bar into place by exerting forward pressure, engaging the lats as the upper arm and elbows maintain an angle close to the upper body.
The pic below is Wade Hooper. He has a low bar positioning. Notice his elbow positioning:
Nobody does it better.