Stuart McGill

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.

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.

And then I took another four students who had the ropes on the next coffee can and then on the next coffee can. And then I'd say, okay, group, flex the spine forward. So the students on the front would pull a little bit, but the guy on top had to pull more than the next coffee can, and then the next coffee can a little bit less, vice versa.

And then I took another four students who had the ropes on the next coffee can and then on the next coffee can. And then I'd say, okay, group, flex the spine forward. So the students on the front would pull a little bit, but the guy on top had to pull more than the next coffee can, and then the next coffee can a little bit less, vice versa.

And then I took another four students who had the ropes on the next coffee can and then on the next coffee can. And then I'd say, okay, group, flex the spine forward. So the students on the front would pull a little bit, but the guy on top had to pull more than the next coffee can, and then the next coffee can a little bit less, vice versa.

The people on the other side had to pay out the rope in sequence. And then I would say, okay, now let's twist a little bit. Anyway, you could imagine it was impossible to control. And then I took out the tennis balls And I put in what was a disc, a big round cylindrical piece of foam rubber. All of a sudden that added stiffness. So now, because the body uses stiffness as the control parameter.

The people on the other side had to pay out the rope in sequence. And then I would say, okay, now let's twist a little bit. Anyway, you could imagine it was impossible to control. And then I took out the tennis balls And I put in what was a disc, a big round cylindrical piece of foam rubber. All of a sudden that added stiffness. So now, because the body uses stiffness as the control parameter.

The people on the other side had to pay out the rope in sequence. And then I would say, okay, now let's twist a little bit. Anyway, you could imagine it was impossible to control. And then I took out the tennis balls And I put in what was a disc, a big round cylindrical piece of foam rubber. All of a sudden that added stiffness. So now, because the body uses stiffness as the control parameter.

Now we've added control in that the foam rubber would create a buffer. And as the deviation in motion occurred, the foam rubber would add more resistance. So it was an automatic control. And that's what a shock absorber does on a car. It has an elastic element plus the damper, but it's the elastic element. And we're going to talk about stiffness and stability, I hope.

Now we've added control in that the foam rubber would create a buffer. And as the deviation in motion occurred, the foam rubber would add more resistance. So it was an automatic control. And that's what a shock absorber does on a car. It has an elastic element plus the damper, but it's the elastic element. And we're going to talk about stiffness and stability, I hope.

Now we've added control in that the foam rubber would create a buffer. And as the deviation in motion occurred, the foam rubber would add more resistance. So it was an automatic control. And that's what a shock absorber does on a car. It has an elastic element plus the damper, but it's the elastic element. And we're going to talk about stiffness and stability, I hope.

that really creates the control. So that's why we have evolved discs. It's highly efficient. I can bend the spine to tie my shoe, but if I have to carry home these days, heavy shopping bags, I need stiffness of that flexible rod so it doesn't collapse.

that really creates the control. So that's why we have evolved discs. It's highly efficient. I can bend the spine to tie my shoe, but if I have to carry home these days, heavy shopping bags, I need stiffness of that flexible rod so it doesn't collapse.

that really creates the control. So that's why we have evolved discs. It's highly efficient. I can bend the spine to tie my shoe, but if I have to carry home these days, heavy shopping bags, I need stiffness of that flexible rod so it doesn't collapse.

Or years ago, I might have been carrying home an animal for dinner and I needed those discs to provide the stiffness in a very economical way and in a way that didn't create stress concentrations the way ball and socket joints would. So that's an evolutionary necessity.

Or years ago, I might have been carrying home an animal for dinner and I needed those discs to provide the stiffness in a very economical way and in a way that didn't create stress concentrations the way ball and socket joints would. So that's an evolutionary necessity.

Or years ago, I might have been carrying home an animal for dinner and I needed those discs to provide the stiffness in a very economical way and in a way that didn't create stress concentrations the way ball and socket joints would. So that's an evolutionary necessity.

Also when we look at spines, there are the column of vertebrae with the intervening discs, but behind them there's two more joints and those are called facet joints and they guide motion. Those facet joints have a variety of angles. They can have open angles which allow you to twist. So if you took a group of golfers, could you imagine if they had facet angles like this, you can't twist.

Also when we look at spines, there are the column of vertebrae with the intervening discs, but behind them there's two more joints and those are called facet joints and they guide motion. Those facet joints have a variety of angles. They can have open angles which allow you to twist. So if you took a group of golfers, could you imagine if they had facet angles like this, you can't twist.

Also when we look at spines, there are the column of vertebrae with the intervening discs, but behind them there's two more joints and those are called facet joints and they guide motion. Those facet joints have a variety of angles. They can have open angles which allow you to twist. So if you took a group of golfers, could you imagine if they had facet angles like this, you can't twist.