Why is lifting items “with your back” dangerous? Why can’t back muscles be strengthened?
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Your spine is like a stack of Jenga blocks connected by a string running down the middle.
The string down the middle allows you to push the Jenga blocks over, but in such a way that the tower doesn’t collapse. It simply curls over as the string is pulled taught.
When sitting vertical, the stack of Jenga blocks is pretty strong. An adult human can easily stand on it, if they could keep their balance. It’s not going to get crushed, because the Jenga blocks are really strong. The string doesn’t really come into play here.
But flex the tower over into a crane-like shape, and now the string becomes vitally important. It’s the only thing holding the tower together. If that string broke, the whole thing would come apart. And the string isn’t nearly as strong as the blocks are, so snapping the string isn’t exactly that hard to do.
When you “lift with your back”, you’re bending your spine over like the Jenga tower, and trying to not only hold up your body like that, but also pick up an unbalanced load like a crane, and hoist all of that load to an upright standing position. The connective tissues between your vertebrae are strained doing this, like the string. Continuously straining them like this can lead to long-term damage and back pain.
When you “lift with your knees”, what you’re *really* doing is trying to keep your back straight and vertical. Keep the Jenga blocks stacked in that really strong configuration. This minimizes damage to your spine, as you are putting loads on it that it is far better equipped to handle.
There’s nothing wrong with lifting with your back *per se*, and in fact it can be good for you… If done properly. The problem is that most people don’t know proper technique. Broadly speaking, if you lift properly you can distribute the load evenly across your back. If you lift improperly the load will be focused on individual discs, and can also place the load on various discs as you go through spinal flexion (which you shouldn’t with a load). Lifting poorly is a recipe for causing back injury, since you are essentially sliding a load across your spine, basically like scanning for the weak point and causing damage there. Imagine your spine as a stack of jenga bricks and you go through hitting all of them in sequence. That’s what you do when you lift poorly. When you lift properly it’s more like putting a weight on the top of the tower.
Assuming you have deadlifted consistently for some time and are familiar with the required form there is no issue lifting your back. The vast majority of people deadlift much more than they squat and the incidence of injury during a squat is marginally higher than that of the deadlift (link below).
This is untrue for the untrained lifter as they will arch their lumbar spine without stabilizing it, injuring themselves.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6059276/
As some have mentioned, proper technique minimizes damaging vertebral discs (rubbery discs between each bone in the spine) but also you minimize damage to the muscles that allow movement and spinal support. Unfortunately, back muscles are relatively small and weak (biceps vs thumb muscles would be analogous to legs vs back muscles). So, lifting heavy objects with small muscles invites injury.
Also, rotation can have a huge impact on how forces are distributed and absorbed (or not). Lifting with your back, you can introduce a rotational movement while picking up or carrying. If lifting with legs, hopefully keeping that in the front of your mind reduces any tendency to rotate your spine and instead use legs and hip girdle to rotate.
Your spine is [chunks of bone strung together with discs of jelly inbetween](https://www.builtlean.com/wp-content/uploads/2016/04/Herniated-Disc.jpg).
The jelly is tough, but not indestructible.
When your spine is upright, the bones remain parallel, the weight is distributed evenly all the way around the discs, and they can cope with that easily. Even if you lift more than your own weight, it’s nicely spread out.
If you put strain on it while it’s bent, however, it pinches the shit out of those discs. Imagine sticking your fingers in the hinge-gap of a door – how hard would someone have to push it, to mash your fingers to hamburger?
And once you fuck up a disc, it *stays* fucked.
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