Eli5: What happens when you “throw your back out”? Why does it seem to happen easier as you get older?

Question

You know, you reach down to close the cupboard, and Whamo. Shooting pain, inability to stand straight up without holding on to something. What is happening?

In: Biology

Answer 1

A lot of people are just pulling/straining a muscle when this happens too, like the multifidus. Same phenomenon causes it as causes disc herniation and some other disc issues. Basically there’s a muscle weakness (at least relative to the load applied), and if you lean or twist just a bit too far, you overdo it and have a pull. That one is easier when you’re older largely due to immobility–kids roll around and are generally limber, while over 50 you tend not to contort yourself regularly.