The title of this post is an homage to the wonderful Katy Bowman's post R U A Rib Thruster. As she mentions, people tend to hide their hunched upper backs (kyphosis it's called) by thrusting (or popping, or shearing, it's all the same thing) their ribs forward at just one joint.
Here. I'll show you me doing it in 2008:
It's like I live to embarrass myself by showing you my past poor alignment.
But hey, I've gotten way better at the whole functional movement thing, and at least this way I'm not picking on some random stranger off the internet eh? Also, I KNOW I was in pain back in 2008 and I know I am not now, so...
Ever wonder why so many bridges contain arches?
It's because a well-constructed arch can hold SO much weight, and also adjust to changing conditions.
See: our spines.
In the photo on the left, these pencils might not all be the sharpest in the box (because I was too lazy to sharpen them pre-photo) but it doesn't matter: spines have lots of redundancy built in. They're amazing structures really!
In the photo on the right, they're STILL not the sharpest pencils in the box, but now it matters because instead of a functional arch, there's only movement/articulation between those two pink pencils.
Those of us (like, pretty much all of us) who thrust our ribcages forward thinking that's how you 'stand up straight' are doing this to our spines - often the joint between T11 & T12 - ALL the time.
If you think 'lifting your chest' or 'sticking your chest out' is what standing up straight is, you are misinformed. Pretty much everyone is - see these VERY educational photos.
Wearing away at one joint like that?
Also, you don't stack your top over your bottom and that means the bones lower down don't receive enough pressure to get the signal that they need to build mass.