In my twenties and thirties I commonly "pulled my back." My lower back would seize up. The muscles I now know as the QL and lumbar paraspinals would go into very painful spasm, and I could barely walk. I could be out of commission for days. Heat and cold; lying flat on the floor with my knees up; nothing was terribly effective. Finally I went to a chiropractor. I don't recollect his treatment doing me any good, but he handed me a sheet of paper with "back exercises" on it, to take home. Mostly they were a few simple, easy yoga positions. I started doing them. Gingerly, at first. (You become very reluctant to do anything that will set off spasm again, when you have back trouble, which generally compounds the problem, adding immobility to the list of your back's difficulties.) But they felt really good. I had no theory to account for it, in those days, but it soon became apparent to me that they worked. In fact, I rapidly became aware that if I skipped them one day, I would start experiencing warning twinges. If I skipped them two, I was at high risk for "pulling my back" again. If I skipped longer, I was asking for trouble, and usually got it.
So, after a few painful lessons, I almost never skip, and never skip more than one day. Even I respond to as clear-cut a punishment-and-reward training system as that. And I haven't had that sort of serious, debilitating back spasm for fifteen years. I had thought it was simply going to be the way life was: that it happened in response to stress, and the idea that the stress of my life was going to suddenly go away was laughable.
Which brings me to stress. Now, it's true that these seize-ups usually happened at times of high stress. The last one I remember was when I was studying for the final exam in a wickedly difficult computer science class on compilers. I was very wrought up about it. I was studying long hours, and spending a lot of stressed time at the computer. When I thought of why my back seized up, "stress" was the answer that came to me.
I am a great fan of getting stress out of one's life; of tackling it directly, by meditation, and by simply getting out of situations in which one is subject to impossible demands. And the correlation between stress and myofascial pain is beyond doubt. However. There's a certain irreducible amount of stress involved in being alive. And there is considerable stress involved in delightful, even ecstatic events: ask anyone who's ever had a wedding. A life without stress would probably not be worth living. And moreover, as science professors keep forlornly saying (knowing that no one will pay attention to them), "correlation is not causation."
The problem with attributing my back spasms to stress is that "stress" is an amorphous condition, and one that responds slowly to direct attack. Meditation and yoga and so forth do make one much better at letting go of stress -- but they do so slowly, over weeks and months and years, not in days. In general the only way out of overstressful conditions -- bad jobs, bad marriages, financial scrapes -- involves incurring even more stress, for some time. Your back is not going to wait that long.
And fortunately, it doesn't have to wait that long. Getting rid of the stress is an admirable goal, but you can stop abusing your body without getting rid of the stress. In fact, the sequence may work better in reverse: you may have more luck reducing your stress by stopping the abuse of your body, than vice versa. I don't believe worrying about my compiler exam brought my back to spasm. Sitting motionless in a badly designed chair with no lumbar support, under a blasting air conditioner, with my shoulders hunched and my head thrust forward -- that's what brought my back to spasm. Not taking the trouble to ensure a dark, quiet place to get a full night's sleep, and staying up too late, night after night. Going for weeks without aerobic exercise.
None of this is rocket science: and all of it can be dealt with by a stressed person nearly as well as by a relaxed person. The body, fortunately for us, is a physical object, and it responds beautifully to physical interventions.