system
Given the following post, respond as if you're commenting on Reddit:
human
What does it mean when you "throw out your back"?

I've never actually done it, and googling the question returns no useful results.

At a biological level, what happens?
gpt
It's not really a specific condition, but more so a general way of describing (typically lower) back pain. There can be a lot of things at play here. Usually it's just a strained muscle and will heal with just some basic rest, but sometimes it can be something a bit more serious like a herniated (slipped) disc. When this happens one of the discs in your (again usually lower) back has torn part of its fibrocartilage and has a bit of the softer inner squishy bits protruding from it. Usually quite painful, but will often heal on its own given enough time (occasionally requires surgical intervention).

Muscle strains are a fairly straightforward process (over exertion causes muscle tear), but actual vertebral injuries are almost always a result of prolonged "wear and tear". Too much pressure over too much time causes something to shift where it shouldn't be shifted. Pretty natural part of the aging process (but overall your lower back is a champ), but clearly doing hard physical labor can significantly speed up the process.

And that, kids, is why you always lift with your legs.