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The number one cause of lower spine problems is too much gravity, although you could throw in inertia, too. There would be no inertia without gravity, I guess. Anyway, the constant downward force of our upper body's weight on our lower spine squeezes discs, causing them to bulge. No gravity, no squeezing, except for trauma caused by changes in inertia, changes in direction, and sudden stops. Obviously, if you fall from a height, come to a sudden stop, or change direction violently in an accident, your spine can also be compressed, and the discs will bulge then also. However, gravity is also a necessary part of normal disc function.
There is no escaping gravity, unless you have millions of dollars and can pay your way into space as a tourist or you are an astronaut, cosmonaut, or taikonaut. But even space travelers have back pain. Their back pain is caused by the lack of gravity. This situation also occurs on planet Earth, when you lie down for too long. Gravity no longer compresses your spine. The lack of compression allows the discs to expand. This expansion is necessary on Earth because it allows nutrients to enter the disk. Compression pushes waste products out of the discs. In the outer space, zero-g environment (and if you lie in bed for too long) there is no compression of the spine to relieve the expansion of the discs. Then expansion leads to pain.
The take home message here is that your spine needs active compression (standing or sitting in a gravitational field) and expansion (which occurs at rest). Without both phases you decrease the well-being of your discs. Be active. Also, rest when needed. Your lower back will thank you, and hurt much less often.