As clinicians, we are often required to fill compensation forms. We are asked to identify the event that caused the injury.
Often, the culminating event that people associate with the pain onset is wrongly considered as the main cause of it. Efforts are now focused on that event.
There are in fact 2 main mechanisms leading to mechanical back pain.
A load that exceeds the failure tolerance of the tissue, applied once, can produce injury - think of trying to beat your PB at deadlifting.
Cumulative trauma from repetitive subfailure magnitude loads can also produce injury. In that case, pain is due to either repetitive application of relative low load - think of gardening - or the application of a sustained load for a long time - think of sitting -.
To sum it up, you can injure your back through high load, repetitive low load or sustained low load.