It's to throw your back out so that you cannot hunch over paint without mortal agony. Suddenly, as the stabbing between your vertebrae kicks in like a small, angry mouse with an acid-coated rapier on your back, the Muse is revitalized. She leaps into action. She had IDEAS. For big paintings. Cool paintings. Fantastic paintings. Paintings that you can't possibly hope to do, 'cos you can just about manage to sit upright without screaming.
The really obnoxious thing about this is that I managed to throw my back out while standing upright, carrying nothing, lifting nothing, gazing straight ahead, not twisted, not ginked, in as close to an approximation of normal human posture as my slouchy form can manage. And something went "twiiiingoink!" and now it hurts like blazes.
Were I back in AZ, I'd limp over to my folks' place and use their weird gyroscopic rack thing, which looks like an ancient torture device but is surprisingly effective at de-agonizing the back. However, now I just have to limp through finishing up a Digger to meet deadline, and then I'll lay on the couch and contemplate raiding the stash of Vicodin I had laid in against this sort of eventality.