Stuart McGill

Imagine if I took a thin willow branch. I could bend that willow branch back and forth over and over and it wouldn't accumulate stress. But if I took that same willow branch and loaded it top to bottom like an I-beam, It would just bend and break. So it supports bending cycles, but it doesn't support compression. Now I'm going to change that willow branch into a thicker stick.

And I bend the stick once and it shatters. In other words, the... Thickness and radial diameter being larger means the stress is bigger in bending. However, let's compress the same stick. It can bear tremendous compression. So there's a very fast example on spines. There's a fellow who has the world record in consecutive sit-ups, thousands of them.

And I bend the stick once and it shatters. In other words, the... Thickness and radial diameter being larger means the stress is bigger in bending. However, let's compress the same stick. It can bear tremendous compression. So there's a very fast example on spines. There's a fellow who has the world record in consecutive sit-ups, thousands of them.

And I bend the stick once and it shatters. In other words, the... Thickness and radial diameter being larger means the stress is bigger in bending. However, let's compress the same stick. It can bear tremendous compression. So there's a very fast example on spines. There's a fellow who has the world record in consecutive sit-ups, thousands of them.

Given what I've just said, what's your prediction? Do you think he has a big strong fellow with a thick spine? Or do you think he's a very slender man with a willowy thin spine?

Given what I've just said, what's your prediction? Do you think he has a big strong fellow with a thick spine? Or do you think he's a very slender man with a willowy thin spine?

Given what I've just said, what's your prediction? Do you think he has a big strong fellow with a thick spine? Or do you think he's a very slender man with a willowy thin spine?

Bingo. He has to be. There's no option. So there's a start on the genetics. Not everybody can play offensive tackle and not everybody can be a gymnast or not everybody can simply tolerate sitting in a chair being a computer operator.

Bingo. He has to be. There's no option. So there's a start on the genetics. Not everybody can play offensive tackle and not everybody can be a gymnast or not everybody can simply tolerate sitting in a chair being a computer operator.

Bingo. He has to be. There's no option. So there's a start on the genetics. Not everybody can play offensive tackle and not everybody can be a gymnast or not everybody can simply tolerate sitting in a chair being a computer operator.

Absolutely, yeah. So the knee width, the bialio-crystal width, which is the width of your iliac crests, hip width are all surrogates to indicate general heaviness of the skeleton. So yes, that's one good marker. But there's more to the story for genetics and how bendy a spine can be. The shape of the disc matters.

Absolutely, yeah. So the knee width, the bialio-crystal width, which is the width of your iliac crests, hip width are all surrogates to indicate general heaviness of the skeleton. So yes, that's one good marker. But there's more to the story for genetics and how bendy a spine can be. The shape of the disc matters.

Absolutely, yeah. So the knee width, the bialio-crystal width, which is the width of your iliac crests, hip width are all surrogates to indicate general heaviness of the skeleton. So yes, that's one good marker. But there's more to the story for genetics and how bendy a spine can be. The shape of the disc matters.

So if you take, on average, a group of top golfers, you'll notice that their spines, that the disc shape, if we were to cut through, which is a transverse scan on an MRI, the discs are more ovoid. if you take someone who can bear a lot of compressive load, the discs look more like a lima bean, and that's called a limacon-shaped disc.

So if you take, on average, a group of top golfers, you'll notice that their spines, that the disc shape, if we were to cut through, which is a transverse scan on an MRI, the discs are more ovoid. if you take someone who can bear a lot of compressive load, the discs look more like a lima bean, and that's called a limacon-shaped disc.

So if you take, on average, a group of top golfers, you'll notice that their spines, that the disc shape, if we were to cut through, which is a transverse scan on an MRI, the discs are more ovoid. if you take someone who can bear a lot of compressive load, the discs look more like a lima bean, and that's called a limacon-shaped disc.

Yeah. We evolved discs and there really is no other better architecture. People say, well, why don't we have ball and socket joints in our spine? And the reason is this. Can you imagine stacking five oranges, one on top of the other, and then you could make them mobile by putting a ball and socket joint in between them. The amount of control that you would need on every single orange is

Yeah. We evolved discs and there really is no other better architecture. People say, well, why don't we have ball and socket joints in our spine? And the reason is this. Can you imagine stacking five oranges, one on top of the other, and then you could make them mobile by putting a ball and socket joint in between them. The amount of control that you would need on every single orange is

Yeah. We evolved discs and there really is no other better architecture. People say, well, why don't we have ball and socket joints in our spine? And the reason is this. Can you imagine stacking five oranges, one on top of the other, and then you could make them mobile by putting a ball and socket joint in between them. The amount of control that you would need on every single orange is

You move one orange, you have to control all the others. It's mission impossible. I would do an experiment with students in my lectures. I would take four coffee cans and put a tennis ball between each coffee can. And then I would put a rope at the front and the back of each coffee can and then one on the side. And I had four students take those four ropes.