[quote]Massthetics wrote:
Lorez, I still don’t quite see how rounding your back can be okay even if your the most muscular person on the planet. Our spines are designed to handle large compressive forces, which is its very hard to injure your back doing squats. However SHEAR forces are what they are NOT designed to handle and its very easy to snap your shit up. This is why dead lifting can be dangerous and you need to keep your spine in a natural position. If you are rounding your lower back, like klokov for example, you are putting an immense amount of shear force on that spine. I don’t care how strong you are, load is load. Correct me if im wrong though but thats my understanding…[/quote]
You have the right basic idea.
To your first point, the amount of shear force experienced is very much dependent on the angle. Looking at things in a very isolated and simplified sense… if the force is in line with the spine, it experiences 100% compressive force and 0% shear force; if it’s perpendicular, it’s 100% shear force and 0% compression.
Then there’s basically a threshold that defines “how much shear force is too much”. The spine can handle some shear force; too much and you have a problem.
Putting those two ideas together, that gives you a range of angles where the shear force is within the threshold, and a range where it’s not. Hence the “some rounding is ok, too much is bad”.
To the second point, you’re oversimplifying. The weight that’s lifted is not being supported entirely by the spine. There’s a complex system of tendons, ligaments, fascia, muscle, and bone that work together to share the load. On top of that (or, underneath), you have additional systems of gases and fluids that also are able to share the load.
You hold a book out and let it go, and the air doesn’t support it… but if you put that air inside of a container like a balloon or air mattress, it’s capable of supporting quite a bit of weight. This is basically what happens when you take a breath and hold it. It’s also why your blood pressure shoots up when lifting a heavy weight.
So taking all of that and applying it to reality. If you take someone completely inexperienced with lifting, they don’t know how to use (or can’t use) intra-abdominal pressure nor create tightness with the muscle and fascia structure. So when they deadlift with a round back, a lot of that force is actually borne by the spine itself.
But you take someone who has the ability to do all of that, their spine bears much less of that load even with much heavier weights. The spine is still part of the whole system, but it’s not supporting much of the weight at all.