The general public often like to use the expression ‘crack bones’ but we like to say ‘click joints’. 
Time and time again I hear from a patient “it’s just muscular” and time and time again the reason why the area in question is sore is because the spinal mechanics (the joints) are not moving how they should.
Both the muscles and the bones work in unison in any part of the body.
Has your back ever popped when you’ve lifted something heavy, or awkwardly? This is usually the facet joint (the joints between the vertebrae) cavitating and locking in position. When this happens, the surrounding muscles will go into spasm to protect the area. Usually the day after, things can be much worse. Any movement will cause pain in the area, especially the muscles that are guarding the area affected. This is the reason why people think that it is just a muscular pain.
Alternatively, you may lift something heavy and indeed strain the muscles of the lower back. This will cause them to tighten. Because muscles attach to the spine, the spine will be indirectly affected as the muscle contraction will be pulling on the attachment to the spine thus causing a spinal restriction.
I like to use this analogy so patients can better understand the issue:
Think of a tent. The pole is the spine and the sheet is the muscles. If the pole is not positioned correctly the sheet will not fit correctly. This is kind of what happens when the spinal mechanics are altered; the muscles will tighten as they won’t be able to move normally due to the restriction in the movement of the spine.
Hopefully this demonstrates why it’s important to treat all the area in question when an injury occurs. We treat the muscle spasm/contraction and also release the joints where these muscles attach to. In my experience, this treatment gets the quickest resolve to the majority of mechanically lower back injuries, therefore saving you both time and money.