We're 2 legged creatures with bad habits...be more surprised when you don't have low back pain (LBP) than when you do.
That really is all I want to say about lower back pain, but of course I should elaborate. Or should I?
Ok, I will.
The spinal column is another really cool body design. It is a series of curves starting just under the base of the skull and ending deep in the folds of the buttocks. The bony structure protects the spinal cord, the large nervous system structure that sends information on an elevator of "tracts" up and down to the brain stem. The bony structure has joint surfaces just like any other joint surface in the body as well as a really cool "inter joint" bone-disc-bone system. Many people think the spinal disc is part of the spinal cord, and it is not, it is a pad between the bones of the spine and has several specific functions related to being a shock absorber. The two mechanisms combine to create a flexible structure allowing us to bend, roll and extend our appendages. Think of the spine as the core of the core, the base for our limbs, the foundation of our building. Ugh, ok I'll stop! Point is, we can only build out from the base what our foundation can withstand. Meaning many of us attempt to reach and lift what our arms can handle, not what our foundation can handle. But our foundation is also not a solid anchor. It is flexible, and as such when we bend and pick up or reach and lift the anchor yields to permit that. When the loads are heavier than the anchor can support micro stresses (or macro) occur. Why don't we fracture our spines or herniate discs on a regular basis then? Because like all of our joints we have muscles that move the spine in all of these directions, and the forces are absorbed and created by those muscles. Unfortunately like our eyes at an all you can eat buffet our arms and legs are often much stronger than our core muscles and over estimate what our spines can truly handle by way of force. When we lift more than our core can handle, or move in and out of posture extremes the weakest of the core muscles takes the stress. If they cannot handle this it goes to the ligaments, the joints, the capsule, the disc, the disc anchor points and the interfaces of these structures with one another. Pain may occur from some or several of these structures at once. Knowing exactly which structure is the source is less important than you may think since the solutions to managing the pain is relatively similar...and starts with moving, properly of course.
The value of a good physical therapy examination may be in determining which of the many choices of activities (various yoga types, pilates, Alexander technique, stretching, dance, massage, chiropractic care), are best when your back hurts acutely, and as you recover, as well as to minimize recurrence or maximize longevity without occurrence.
The bottom line should not be that back pain occurs but rather how much we can do despite it.