There's not so much you can do about it at work, but at home make sure you have a decent chair to sit in. Don't sit on the floor if you can avoid it (occasionally is fine, of course). It's well worth buying a chair that is comfortable and fits your body size.* Having just a week ago been to visit a carpenter and discussing chairs (and tables) I can confirm that Japanese chairs are 3cm shorter than British ones. That doesn't seem a lot, but long term it'll screw up your back. Not lugging around huge great gaming bags helps, too
*where to buy such a thing: Nitori, Furniture Dome and other such emporia all sell adjustable office chairs. Cheap ones are rubbish, but a decent one can be damn comfy. Eg my games-room/painty chair was bought in Nitori for about 2man or so, I think.
Ps - exercise is a good idea, too. The back is basically a whole passel of muscles and ligaments and other such technical gubbins. Like the brain, if you train em, they get better at what they're supposed to do and less likely to stall when called upon.
Most of it due to travelling with parents in golden week and general life stress I'm sure. It's got to be about the 4th or 5th time I've done this since coming to Japan. Floors, small chairs etc, painting and Internet use take their toll after a while. Low calcium in the diet?
