system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is lifting items “with your back” dangerous? Why can’t back muscles be strengthened?
gpt
While you sure can injure your back muscles and that is a significant risk (due to the leverage disadvantages of your back muscles vs. your arms when pivoting on the spine), the main issue is your spine. It's very easy to slip a disk, or otherwise onjure your spine, when trying to lift a heavy load with your back.

And "very easy" here is not a hyperbole. It really is VERY easy. People have thrown their backs out trying to lift trivial weights, usually specifically because the object was so light that they didn't even consider it "lifting". It's usually due to repeat strain.

If you lift with your legs, back straight, that force is supported vertically, which is the direction your spine is strongest. It also means your back muscles don't have to do such a disproportionate amount of work.