When I was 23 and in grad school I would blow off steam by going to the batting cages and whaling away on 55 mph meatballs (didn't have a jam space to DOOOM, what could I do?). It was also a period of substantial weight gain. Anyway, the pitching machine broke while I was in the cage... it kept giving me freebies- it just didn't stop. "Woohoo! Free batting practice!" I thought and I gleefully hacked away for the next 20 minutes, wearing holes in my batting gloves, blistering my fingers, finally leaving with exhaustion with the machine still pitching.. oh yeah and my lower back was a bit sore..
The next day I literally COULD NOT WALK. I do believe I herniated a disc in that cage. Ever since, it's been prone to aggravation. If I tweak it, I'm hobbling for a week or more. It's especially vulnerable if I've been putting on the pounds.
I hate to admit it, but the best cure I've found is this guy:
Diamond Dallas Page
his "red hot core" workout on the first DVD is the quickest fix to the tweaked lower back I've found.
And yes, @askrere, before you mention it, those AARP discounts are sweet. They got a special on NOS carbon comp resistors and nixie tubes this week!