Let me try to explain what is happening.

The sequence of events in the production of symptoms of back pain

The result of the "repetitive strain", whatever its cause, is local pain which causes muscle tightness, usually one sided. Because muscles attach to bones this increased tension pulls the bone(s) out of alignment with its neighbours.
All bones, particularly the spine, have a natural range of movement that is normal and comfortable, but once that movement is compromised, and the bone is "jammed against the backstops" then further pain arises from the capsule, or covering, of the facet joints.

Pain from the facet joints causes more local muscle spasm and initiates a vicious cycle. Further pain arises from joints at either end of the jammed segment of spine - they have to move more to make up for their neighbours' limited movement.