While there are many physical culprits that we can identify in cases of back pain - sprains, strains, discs, etc. - the biggest culprit that causes pain to flare up are our habits. In sport, at work, during life, certain ways that we move (or don't move) can be the determining factor pain-onset, whether x-rays show structural defects or not.
Allow me to be clear in that "bad posture" does not cause back pain. New studies now find that poor posture, in fact, correlates quite poorly to future pain.
I read an excellent quote, however, stating this:
In reality, the fact that we sit or stand a certain way does not result in us experiencing pain. Rather, it's the fact that we hold those idle positions for too long. The body craves movements, and so delivering on this can have great results. Regular breaks from sitting at work, for instance, has excellent benefits on preventing pain.
Solution: Move more.
As another clarification, repetition, inherently, is not bad for you. Our hips move in a forward-and-backward motion to allow us to walk all day, every day, and you don't see the majority of the walking population collapsing due to overuse hip injuries.
The problems arise when the body is not properly conditioned for the particular movement being repeated.
Many runners perform fine without injury occurrence, but the one's that are not properly trained to drive strength from their hips will encounter problems.
As a non-sport example, many housekeepers won't be bothered by the amount of windows they clean. Just the ones that overuse their wrists and elbows instead of utilizing the large muscles from their shoulders.
In short, the body is able to handle just about any repetitive activity. However, depending on the volume and frequency of those movements, a certain level of strength and endurance may be needed.
Solution: Move differently.