I messed up my back last week. It wasn't terrible, but I endured five days of wincing every time I tried to bend over or straighten up. Naturally, this happened just before I had to move every single item in our attic in preparation for an insulation and air sealing project plus carry a bunch of stuff down the stairs and out to the alley.
It wouldn't be a big deal—I've had minor backaches occasionally and this one wasn't really any different—except for the way I hurt myself. Lifting something too heavy? Not bending my knees? Nope. Actually, it did not involve lifting at all. I hurt my back by sitting down on the couch. I don't know; I guess my butt didn't land in quite the right spot and my back got jammed up somehow. Anyway, the point is that people in their 20s don't injure themselves so casually. But apparently 40-somethings do.