I recently saw a research article that talked about the role of exercise in managing back pain. The study was trying to determine what type of exercise is best for low back sufferers. The researchers divided the back pain folks into one group doing only general exercise such as walking, and the other group doing only very specific low back rehab type exercises.
The results of the study was that general exercise, i.e. not specific to the lower back, seemed to give more relief in the long run.
I'm not surprised that general exercise and activity help the lower back. In fact, prior research has confirmed that being fit makes you less likely to have problems with your lower back. General aerobic exercise absolutely helps the lower back.
I think the wrong take-home message from this study would be that specific low back exercises (i.e. low back extensor muscle strengthening, hamstring stretching, abdominal crunches, core work, and so on) are not useful for those with low back problems. The study really did not customize the low back exercises and that was a mistake.
Not all "low back" problems are the same, and different ones require different specific exercises.
If you have low back problems, by all means work on improving your overall fitness levels, but also get things checked out and learn the correct low back preventive exercises for you. In my experience, consistently combining the two will give you the best long-term results.