Lower back ache the day after squatting

[Mr.City]

For me, it's been letting my chest collapse on the final reps of a set and loosing my grip on the bar, letting my elbows drop.

[StickFigure]

WTF is PNF, please?

PNF=Proprioceptive Neuromuscular Facilitation

How to do it: Stretch a muscle for 15 seconds against an unmovable object (wall, post, etc..)...then while stretching flex that muscle for 10 seconds, as if trying to move that bodypart through it's ROM against the immovable object.....as soon as you relax the muscle, stretch just a little deeper and further and hold for another 15 seconds.

How it works: You go down to max stretch then you flex the muscle that your stretching, this causes your muscle to focus on the flex more than the stretch-reflex response. As soon as you stop flexing you have a 2-3 second window where you body still has its guard down in reference to the stretch-reflex response, this allows you to go into a deeper stretch that you initially could.

[Geezer]

I have just finished watching the SS video, It´s got me thinking that I may have been so concerned about rounding my back that I was overcompensating and therefore over-extending(???I think thats the term, the opposite of rounding).

Does that sound like the likely culprit? I gave my back a rest from squats for a week and ache has completely gone away.

Stickfigure: interesting stretching info, thanks.