The Incredible Human Foot Dissected

We're about to embark on something

most of us have never witnessed before.

It will take us inside two of the most extraordinary

structures in the natural world.

Our feet and hands.

Two parts of our body that make us who we are.

I'm George McGavin, and as a biologist, I think that

to truly understand our feet and hands, we need to look inside them.

To do this, we've created our own dissection lab.

We've brought together the tools, the technology

and leading experts in human anatomy.

Over two programmes, we're going to dissect a human foot and hand,

to discover what makes them unique.

And this time, we're looking at feet.

We're going to reveal them as you've never seen them before.

We'll take the foot apart systematically...

We have to take the plantar fascia here and pull it back.

..to uncover the incredible natural engineering

that carries our weight and drives every step we take.

That is the first time I've seen...inside the foot.

Beyond the lab, I'll look at other animals whose feet give us

clues to the origins of our own.

So, my right foot is slightly more orang-like than my left foot?

-Absolutely, yeah.

-That's fantastic.

And I want to discover exactly how our feet give us

something that's rare in the animal kingdom, yet vital to our lives -

the ability to balance on two feet.

Oh, Jesus!

I do...I don't want to move my legs.

Taking a foot apart will be challenging,

and it might provoke a strong reaction.

But it will reveal how this extraordinary

part of our anatomy has allowed us to stand

and walk upright - fundamental abilities that define us as human.

Of all life on our planet, no other animal has feet like ours.

They allow us to walk on two legs -

possibly the most significant step in our evolution.

Our feet made us mobile and freed up our hands

to use tools - skills that allowed us to dominate the planet.

Our feet bear the weight of our body

and propel our every step and stride -

all the while performing a perpetual

act of balance that keeps us upright.

Yet we rarely think about them.

What we consider to be our greatest physical achievements

depend on our feet.

How fast we run, how high we jump, our agility,

our balance, all depend on the remarkable capabilities of the foot.

To discover how our foot makes all this possible,

we've set up our dissection lab

in the Anatomy Museum of Glasgow University.

And to perform the delicate operation of dissecting

a real human foot, we've brought together an expert team.

Dr Kartik Hariharan is one of the country's leading foot surgeons.

Feet have always fascinated me. They're unique organs.

They're very complex.

And if you look at it, we place very conflicting demands on feet.

We want them to be soft and supple and mobile,

whilst on the other hand, we want them to be rigid and strong,

so that we can push off and propel ourselves.

And it's only because of the finesse of the foot,

its technical complexity, that it is able to offer

both of these functions to you, without too much effort.

Well, I think it's about time

-we actually saw how it all worked.

-Absolutely.

Anatomy expert Dr Quentin Fogg is going to lead our dissecting team.

He has carefully prepared our specimen,

following the strict medical

and ethical protocols that govern the dissection of human tissue.

-Hi, Quentin.

-Hi, George.

-So, this is the foot

-that we're going to dissect?

-Yes. This is the foot and the lower limb

of a person who donated themselves

for anatomical research and education.

Now, to some people this might seem

quite a shocking thing, almost bad taste.

But how would you answer that?

It's quite a commonplace thing in your world, isn't it?

It is, and it's a real opportunity for us to explore

the body in a way that you don't really get in any other format.

You can look at the internet, you can look at amazing drawings

and wonderful photos in books, and you don't really get an

understanding of how it works to the same level as we're going to get.

Our team is ready,

and the moment has come to make the first incision.

It's something few people ever get to see.

I'm fascinated, but also a little apprehensive.

We're going to start off by looking at the sole of the foot,

by cutting the skin here and removing this,

to see the layers directly underneath that.

So I'm going to get started.

And then just going down the side of the foot...

Now, that skin at the heel is pretty tough, isn't it?

Yeah. It's many layers thick,

and a lot of these layers are actually dead skin cells.

The body heaps it all up simply to thicken it up,

so that can act as a shock-absorbing pad.

Ooh, now, the skin's coming right off the heel.

I have to confess, I'm...I'm feeling slightly queasy about this,

and nu...not in a severe way, but it's quite a disturbing view.

That is the first time I've seen...inside the foot.

There's a huge amount of fat there -

just masses of it!

That's fat that's packaged in a very special form to maximise

the shock-absorbing capabilities of the heel.

How is it arranged, though?

Because it looks almost, erm,

-like a, you know, a sponge. Is that fair to say?

-Yeah, well,

Well, it is anything but a sponge, because its strength is phenomenal.

It's almost like a hydraulic pad, where you've got these fat

packets arranged in little discrete sections, with little fibrous walls.

So, they work in a fashion,

so that your weight is distributed quite evenly.

So it's not one big lump - it's not like a cushion.

-It's more like bubble wrap...

-OK, yeah.

..where you've got multiple sections

of fat, so it's able to dissipate

shock and forces that go through it in a much more efficient fashion.

So, in this first stage of our dissection, we've already seen

two vital parts of the foot.

The tough outer skin, and a thick layer of fat beneath,

that combine to act as a shock-absorber.

But our skin has another important function.

To see what that is, there's no way around it -

I'm going to have to bare my own feet.

I'll make an exception! Ha-ha!

-Right, there you go.

-OK.

Now Hari can get his hands on my bare feet,

he can show another crucial role that the skin performs.

A very important function is that of sensitivity -

the ability to perceive touch.

And a very simple example is tickling.

-Yeah!

-Ha-ha-ha!

-He-he(!)

-So, you can see how,

as soon as I put my fingers to your...

to the soles of your feet, you try and retract them away.

So, that is a very important protective mechanism,

so that you don't step on something sharp without recognising it.

Now, it's not just sensation which is

flat and equal across the whole of the foot.

Different parts have different sensations,

and let me try and illustrate that to you.

OK, what I want you to do is, I want you to close your eyes,

so that you can't see what I'm doing.

I want you to tell me how many points you can feel, OK?

-How many points can you feel on that?

-One.

And there?

One.

-And there?

-One.

-There?

-One.

One?

Two.

That's a beautiful illustration of how

the acuteness of sensation changes.

So at the back, in the region of the heel,

where the skin is very thick, it's important to feel pressure.

But as you come towards the toes, your toes will have to do more.

They'll have to be able to feel the shape of things,

the sharpness of things, and so, as I got towards the toes, you were able

to perceive that I was touching you with two points as opposed to one.

Elegant!

So, the soles of our feet have two important functions -

to sense the ground below them and support the weight above them.

But what actually happens when we walk and run?

How do our feet perform these movements

that are so fundamental to our lives?

STARTING PISTOL FIRES

To understand this, we need to take a closer look at our feet in action.

So I've come to Dundee to meet Professor Rami Abboud.

He's an expert in biomechanics - the science of how our body moves.

And he's been researching exactly what our feet are doing

when we walk and run.

We can run a series of tests to show you what happens with the foot

and leg when we walk and run.

Rami is investigating how much pressure

the weight of our body puts on our feet.

So he has assembled an arsenal of technology - cameras,

pressure pads, movement sensors,

all set up to analyse what happens with each footstep.

First, Rami wants to show me what happens when we walk.

As you can see, she hits the ground at the heel, moves forward to the

forefoot, comes off the ground, and this is the normal way we walk.

We all walk in this fashion.

This is the data from the pressure pad.

Red areas show where the pressure on the foot is highest.

We can see this happen when the heel hits the floor.

In fact, up to twice the volunteer's weight

goes through her heel as she lands.

It's why the tough skin and the pad of fat we saw

in our dissection are so important - they help absorb this shock.

And as the rest of the foot comes down,

we can see how the pressure shifts.

You can notice here that most of the pressure that we saw under

the heel is now localised under the ball of the foot -

and we're ready to push forward.

And the last point of contact will come with the toes,

and mainly the big toe.

So that's a complete movement, from heel strike to leaving the ground.

Absolutely.

We take thousands of steps every day,

and each one puts the pressure of twice our body weight on our feet.

Next, Rami's going to show me what's different when we run.

As you can see now from the pressure patterns on the screen,

there is an impact of the forces from heel to toes again,

and the striking point here is that the pressure that you see under the

heel, which is reaching sometimes up to three times your body weight...

-So that's very high.

-That's extremely high.

And the heel will have to try to absorb that.

So, landing on our heel when we run

sends a force three times our body weight up our leg.

And Rami's computer shows us

the direction that the force of the impact travels in.

You can see this massive force that is going through

the system from the ankle all the way to the hip.

The arrow shows that the force from the heel strike is going right

through all the major joints in the leg - the ankle, knee and hip.

And this puts enormous pressure on these vital joints.

What's really obvious is, if you compare this to walking,

there's a point where both feet are clearly off the ground.

-As you see here.

-But every time

the heel comes down and you've got the full body weight

-plus times three, banging away at your joints.

-Absolutely.

This is a repetitive movement that you do during running,

so it's not happening once or twice.

Every year, it's estimated that

up to 75% of regular runners suffer an injury.

Some research suggests that the impact

generated by heel-striking could be a contributing factor.

And Rami's research has revealed something surprising.

It seems the pressure caused by the heel strike could be

a relatively new problem that we humans have inflicted on ourselves.

To see why, we're repeating the running experiment,

but this time, with a difference.

Now this is really interesting.

We've asked Charlotte to run with no shoes on,

and, that's remarkable, there is no heel impact at all.

It's very normal. This is how most of us run.

When we run bare feet, we never land on the heel like we do

when we're walking, we will only run on the ball of the foot.

If you actually try to tend to run heel-to-toe,

you'll be in deep pain, and, if you look at the actual screen there,

all the impact is being taken by the ball of the foot.

You're landing instantly on the most stable position

and structure of the foot.

Landing on the ball of the foot instead of the heel completely

changes the way the force of the impact passes through our body.

As you can see, the actual force is not going through the ankle,

it's actually in front of the ankle, pointed

backwards behind the knee. This force is now absorbed by the calf muscles.

It's not going through the joint.

So, when the ball of the foot strikes the ground first,

our calf muscles are able to take some of the strain off our joints.

So your research is actually indicating that

when we run with shoes on, we're actually running in the wrong way?

Well, absolutely.

As human beings, I think we are born to run, and that goes back

to our ancestors when they used to chase game over long distances.

And they've done that without shoes, or any cushioning material.

Wearing shoes encourages you to land on your heel,

and that might cause serious injury.

Today, it's hard to imagine going about our lives without shoes on.

But although they make our feet feel more comfortable,

it seems wearing them might have an unwelcome consequence.

So it looks like we're not using our feet in the way that

evolution shaped them.

Keeping them warm and protected in shoes

has added to the strain we put on them.

So, with every step we take, our feet cope with huge forces.

But what is it inside the foot that makes this possible?

That's what we're looking for in the next part of our dissection.

Right, where have we got to?

We've just removed the layer of fat, and then we've got

a really important tissue hiding right underneath that.

This is a special layer of tissue, just really like a bunch of strings,

known as the plantar fascia, which is a really important

layer for adding mechanical strength to the sole of the foot.

So you've removed the whole of the sole of the foot, plus all that fat.

Hari, what does that actually do?

This is probably one of the most important structures, particularly

in trying to understand the complex biomechanical workings of the foot.

It connects the heel or the hindfoot to the toes which form the forefoot.

So you've got three structures - the plantar fascia, the heel

and the toes - forming this wonderful weight-bearing system.

The bones of the foot form a familiar structure -

an arch, particularly good for bearing weight.

Its two pillars are the heel and the ball of the foot.

But what's less familiar is the tissue that binds them -

the plantar fascia.

It's a part of the foot most of us

know very little about - yet it's crucial to the way our feet work.

So, you can see this very elegant structure,

taking a point of attachment to the heel,

and then moving forward, very thick to begin with, and bunched up,

and then separating out into many strands like a fan.

This works by tensioning and de-tensioning as you put weight

and you take weight off.

You can actually see this as I put

the foot into a standing position.

-You can see...

-Ah, yeah.

..the thing tenses, and as I relax it,

it becomes a bit looser and floppier.

So, that's a very unique function

of this particular structure,

and it works almost like a spring,

-but a very, very taut and tight spring.

-Wow.

As Quentin continues the dissection,

I want to learn more about how this spring-like mechanism works.

To help me is Dr Niall Macfarlane,

an expert in the biomechanics of the human body.

So, Niall, can you explain to me

some of the essential elements of the physics of the foot?

Yeah, I've got a simple model here that might help.

So, obviously, this part represents your toe.

This is the ankle and this is the heel.

So, the first thing that's important for our gait, for walking,

is to lift our toe.

That muscle action to lift the toe

puts some stress onto the plantar fascia.

I can actually feel that.

As I lift my toe up, my arch is becoming, you know, stretched.

-Yes, that's right.

-Strained.

And that is really important to the physics,

the biomechanics, of the action of the foot.

When we hit the ground and your heel strikes...

So, when we hit the ground, your weight presses down your ankle.

That puts much more energy into that plantar fascia.

It acts like a spring - stores the energy -

and when you lift your foot off the ground to take the next step,

lo and behold,

it springs you in the air

and gives you some energy to take your step forward.

It's essentially an energy store,

-and it's what put's the spring in your step.

-It does, yeah.

So, the foot is an extremely efficient energy converter -

storing energy that comes down through the ankle,

then releasing it to help propel us forward.

But where does power to drive this action come from?

OK, so let's make this incision...

To find what powers our foot, we

need to look beyond the foot itself,

beneath the skin of the lower leg.

We're going to uncover something that's key to our movement -

the calf muscles.

When we open this up, we'll see different types of tissue.

We'll see the yellow tissue that looks like little

collections of sponges - more fat.

How is the power produced in the calf transferred

all the way to the foot?

OK, this is a very good example of probably the biggest muscle

that has its influence in the foot.

This is the muscle in the calf, which then works on the bone.

That is the end point of where this muscle works.

And the conduit for the transfer of that

energy into the heel would be the Achilles tendon.

The Achilles tendon is something I've often heard about.

But now I can actually see why it's so important to how we use our feet.

It's bigger than I imagined - it emerges from the calf muscle

and attaches it to the heel bone.

So if we looked at the tendon

slowly transforming from the muscular structures.

So the muscle ends roughly about here,

and slowly, you find this wonderful tubular structure.

Let me show you how it actually works.

So, at this point, I've let the foot dangle down,

and I'm going to hold the calf muscle here,

and I'm going to squeeze it.

And you can immediately see how, by contracting

and shortening this muscle, you can see the front of the foot

move down, and conversely, the heel actually lifting up.

So that's what happens when you go up on your toes.

That's correct.

If you look at this now, you can

see the anatomic definition very, very nicely.

You've got these two big bellies of muscle that are going down

to attach onto the tendon.

The tendon is very broad here - much narrower further down,

but much thicker, much more concentrated fibres.

You can now appreciate that this tendon is responsible

for us walking, standing, jumping -

-all of the things that we take for granted...

-Mmm.

..in our day-to-day lives.

So, our leg muscles and our Achilles tendon are working together

to provide the power we need for movement.

And this propels our every step and stride,

every jump and leap.

It's what takes us to the pinnacle of our physical achievement.

The deeper we delve into the workings of the foot, the more

it becomes apparent that nature has come up with some incredibly

complex engineering to support our weight and allow us to move around.

We humans move in a way that's

extremely rare in the animal kingdom -

we have four limbs, yet we only use two of them to walk.

So what is that makes our feet different?

To answer that, I've come to the Natural History Museum at

St Andrews University to look at the feet of other four-limbed animals.

Now, in order to move around,

all animals need feet that can perform two basic functions.

They've got to achieve stability AND mobility at the same time.

For some animals, you have to trade off one against the other.

Take the elephant. An adult male can weigh a colossal seven tonnes.

And just to support that enormous weight, their feet have evolved

in particular ways - some of them surprising.

Well, this is the hind foot of a young elephant, and you can see

the bones are extremely strong and thick - this is the heel bone here.

When the elephant moves around,

its foot is actually in this position, and that's because

this space here at the back

is occupied by a massive pad of very specialised fat.

The result of this is that elephants

when they walk are actually walking on tiptoes.

It's a bit like they're wearing high heels, but in this case, the

high heel is formed by this enormous

pad of specialised fat that helps to bear

the enormous weight of the animal and spread it out over a large area.

An elephant is definitely not built for speed.

This is an example of animal

that has had to trade off mobility for stability.

But for other animals,

the ability to run fast is a matter of life and death.

Take the horse or the zebra.

In the wild, these animals evolved for life on the plains.

They needed to cover long distances and outrun their enemies.

For them, mobility is the greater priority,

and their feet look very different to the elephant's,

as we can see when we look at their skeleton.

This is the hip girdle or pelvis.

Here's the femur, the thighbone of the leg.

Kneecap. Here is the lower bone of the leg.

But the really interesting stuff happens further down.

A full one third of the length of a horse's leg is made up by its foot.

This is the ankle joint here, here is the heel bone,

and this is the long bone of the foot.

And if I can compare this to my hand,

we have of course five fingers and toes. In a horse, all that

remains is the middle toe, that runs right the way back up here.

In essence, horses are running on their middle toe.

But running is just one way to cover great distances.

Kangaroos and wallabies do it differently.

And to achieve this, they have evolved very unusual feet.

An animal like a wallaby gets around by hopping, and

so not surprisingly, its hind legs make up about half of its height.

The long bones of a wallaby's foot give it a great

deal of leverage against the ground,

and a second toe off the side here gives it a bit more stability.

But stability can be achieved by other means,

because not all four-limbed animals walk on the ground.

A chameleon is a highly-specialised sort of animal.

It doesn't need to be terribly fast.

What it DOES need to do is hang on to branches very tightly indeed.

And its foot is highly-specialised.

It's called a zygodactyl foot.

Two of its toes go in one direction and three go in the other,

so they can wrap around the branch very tightly indeed.

So, all these animals evolved their own solutions to the

trade-off between stability and mobility.

And this allows them to move around in their different environments.

But although their feet appear very different,

if you look carefully, you can see intriguing

similarities between these diverse animals and us.

If I take as an example the long bone of the middle toe,

it varies a lot from species to species.

Here it is in the wallaby, tiny and slender.

Here it is in the horse, the major bone of the foot.

In the elephant, it's here.

And in the human, here.

And the fact that all these animals have similar

bones in their feet is no coincidence.

When you look at the limbs of a tetrapod animal -

that's a four-legged animal - you see a basic plan.

There's an upper leg or arm bone,

two lower leg or arm bones,

then you get a collection of small bones

in the wrist or in the foot.

And then you've got five fingers or toes.

And that's called the pentadactyl limb.

Pentadactyl - five fingers.

All four-limbed animals today are descended from an ancestor

that lived over 340 million years ago that had a pentadactyl limb.

It's an incredibly versatile basic plan,

that nature has modified in a myriad of ways to allow animals to

stand and move around their environments.

And one of those adaptations

is our own foot, which has evolved in its own unique way.

The pentadactyl limb structure truly is a marvel of nature.

It's a blueprint that evolution has adapted in countless ways to

allow different animals to survive

and move around in all the variety of habitats on Earth.

To me as a biologist,

it's an illustration of evolution at its most elegant and awe-inspiring.

So, our hands and our feet are based on this pentadactyl structure.

And although most of us assume they have very different functions,

we can in fact use them in surprisingly similar ways.

Tom Yendell was born without arms, but that hasn't stopped him

from becoming an artist.

That is absolutely extraordinary.

I mean, I couldn't do that with my hands.

It's 51 years of practice.

When did you draw your first picture?

I think when I was about, er...

Well, I don't know.

I've always used it, so -

-when did you draw YOUR first picture?

-I can't remember.

-Probably about five, I suppose.

-Yeah.

When I was five, I had artificial arms,

and the doctors put socks and shoes on me, so I couldn't use my feet.

And I've got some film of me scribbling with this hook,

and being very frustrated, because I knew I could do it much quicker

and much easier with my feet.

And you use your feet for everything?

Everything. Yeah.

I mean, everything you do with your hands, I do with my feet.

Tom trained his feet to do the everyday tasks that we

take for granted - but he also uses them for painting.

And you're now a very well-respected artist around the world.

Well, I'm an artist!

-And you've got some images here.

-Yeah.

Yeah, I've got some pictures that you can have a look at.

This is what I'm...

What I'm known for really is very "graphicy" flowers.

And I paint for the Mouth and Foot Painting Artists.

We're a group of 800 artists around the world that all

earn their living through painting.

Seeing Tom's work, I'm intrigued by his ability,

-and I'm keen to see how much

-I

-can do with my own feet

So, I think we'll just, just write our names, really.

There you are. Tom Yendell.

Right. Right, OK.

HE HUMS TO HIMSELF IN CONCENTRATION

'As I struggle with the pen,

'I'm struck by how remarkable Tom's ability is.

'MY feet just can't seem to manage the precision

'and control that HE makes look so easy.'

Me O's gone funny.

Right.

-Give me the pen.

-Oh, sorry.

I'll show the audience how it should be spelt.

GEORGE LAUGHS

-What is it, G-E-O-R-G-E, is that right?

-Yeah.

-There you go.

-Brilliant.

Must try harder, eh?

-Must try harder. Practise.

-Yeah.

Use your feet, because they are so useful.

-Take your shoes off when you're at home.

-Yes.

-I think I will, actually.

-Yeah. Be a shoeless environment,

and you'll be amazed at how quickly you can start doing things.

Can I have that as a souvenir?

You can.

I should get you making a paper aeroplane really, shouldn't I?

Oh, come on, Tom! Come on!

Thank you very much.

Through constant practice, Tom can use his feet to do things

that most of us could only achieve with our hands.

But what is it inside his foot that allows him to do this?

That's what Quentin's looking for next.

We're about to unveil all of the intrinsic muscles of the foot,

all the small muscles inside here that control

the toes in different ways.

To see them, we have to take the plantar fascia here,

and pull it back.

And one of the first things we'll notice is the small muscles

underneath here, the lots of little tiny tendons.

And are these ones that we're actually are able to

shift our toes individually with?

-Yeah, these...

-..and wiggle them about?

These are the wiggling muscles. Indeed!

Now, the degree to which individuals are able to wiggle their toe,

that varies quite a bit.

Yes, I think it all depends upon the flexibility of the individual

per se, and how well-developed these muscles are.

So, it's likely that the intrinsic muscles in Tom's feet

are more developed than in most of us.

And this allows him to use his feet with such precision and control.

So, if we look inside the foot here, we can see these small muscles.

And if we lift that up, we see there are these really thin,

slender tendons running down to each individual toe,

apart from the big toe. And if I pull on them as a group...

..the tendons will pull on each toe, and make them move.

If I pull on one at a time,

we don't really get a single movement from just the one toe.

The one next to it will still be working.

If you looked at it in evolutionary terms,

in the time when feet were

used as climbing organs

and grasping organs, these muscles would have been very well developed.

But, of course, the anatomy of the foot would have been different then.

The big toe would have been more like a thumb.

And you would have power and pincer grip, in order to be able to

do the finer movements that's

demanded more of a hand than a foot.

The small, intrinsic muscles in our foot are a remnant from a time

when our ancestors lived in the trees.

And just like primates today,

they used their feet

more like we use our hands -

for holding and grasping.

So what else can the feet of our close cousins tell us

about how our own feet have evolved?

I've come to Chester Zoo to look at the feet of the orang-utan.

Orang-utans are primarily tree dwellers,

just like our early ancestors.

So to find out more about how we came to have the feet

we have today, I want to compare the orangs' feet with our own.

Professor Robin Crompton is a world expert on understanding

how our ancestors walked.

Key to his research is studying modern primates.

How do orang-utans use their feet?

Very much as we'd use our hands.

They have, first of all, a big toe which is like our thumb,

and held at quite an angle to the other fingers.

So they can actually wrap their thumb around a narrow branch,

-a vine, just as we can do with our hands.

-Mmm.

Equally, the rest of the foot can curl around even very narrow

supports like vines and small branches,

to meet and grasp round in a powerful grasp like that.

High-speed cameras capture

the movement of the orang's feet.

They clearly show a distinctive bending motion -

this allows their feet to curl and grip in ways that our foot can't.

This flexibility seems so alien to us,

because our feet appear to be far more rigid.

In fact, for a long time, we thought that having a rigid foot was

a defining feature of humanity -

something that separated us from our primate cousins.

But it seems the story is not so clear-cut.

Robin's been comparing the differences in primate

and human feet when they walk.

To do this, he uses pressure pads.

As the orang-utan walks across, we can see it has an awkward gait,

walking on the side of its foot.

So, this is the classic orang-utan pattern.

We're seeing very little contact under the heel,

a large peak in front of the heel

in the middle part of the foot...

'The red areas show where most pressure is exerted on the pad.

'And Robin is particularly interested

'in this small pressure peak here.'

What's causing this peak is a small joint in the orang's foot.

It's called the mid-tarsal joint.

It's very mobile, and this is what allows the orang's foot to be

so flexible - perfectly adapted for life in the trees.

The human foot also has a mid-tarsal joint,

but it was long believed we'd lost the ability to flex

at this joint - we thought it was locked and rigid.

But Robin isn't so sure.

He's been investigating

whether OUR mid-tarsal joint can still flex today.

So, can he find any evidence of it in my footprint?

There's no sign of it in my left foot,

but in my right foot, there's a surprise.

So, George, this is the still data from your footprint record.

You can see that you produced a mid-tarsal pressure peak.

-This is my foot here? This is my right foot.

-Right there, yep.

You can see it appearing just there, right in between the heel

-and the ball of the foot - in the middle there!

-Oh, yeah, there it is!

This is something that humans are just not supposed to have.

-So my right foot is slightly more orang-like?

-Absolutely, yes.

That's fantastic. That's really, really interesting!

Over the last few years, Robin has been gathering pressure pad

data from large groups of people.

His results challenge what we thought we knew about our feet.

They suggest that far from being locked and rigid,

our mid-tarsal joint can bend when we walk, just like the orang's.

Well, it's quite definitely shown that the human foot is just

nothing like as stiff as we thought it was.

In fact, in our data set, two-thirds of people

produce a substantial mid-foot pressure peak, on both feet,

within five minutes of walking.

Robin's work has shown our feet are not just rigid platforms.

In most of us, the middle of our foot still has a flexible

joint that we've inherited from our ancestors.

So if it isn't our skeleton that makes our foot rigid after all,

what is it?

What's very clear now is that it's primarily the soft tissues -

that is, the ligaments, the muscles and the tendons.

And what they're giving our feet is particularly an adjustable stiffness.

And that's very important, as it turns out, because it's made

a big difference in our ability to adjust to life on the ground.

And the fact that humans retained a foot that essentially

can be flexible when it needs to be, I think almost certainly is

one of the major factors which has made humans so successful

when we started to move out of forest, into open country.

So, it turns out that our feet can be both flexible AND rigid -

and that's what makes them so special.

It was this unique combination that enabled us to adjust

to different terrains, and allowed us to spread across the planet.

One of the crucial factors that gives our feet this exceptional

versatility is the soft tissues that bind our bones together.

And back at our dissection,

Quentin has uncovered some of these.

One of the key structures

in here are ligaments.

And ligaments really

just strap bone to bone.

Their job is to define the range

of movement of the joint.

So, when two bones are next

to each other, they need to be able

to move a little bit - but not

too much, or they fall apart.

-Right.

-So a ligament is

the strap that holds them together.

And in this view of the foot,

we've got lots of little bones here,

and we can see the joints between them.

And then there is one great example from the outside of your ankle

of a big ligament strapping from this bone to the next.

So the really important thing about these,

other than defining the range of motion of these joints,

is that they can help stabilise each of these joints,

make sure they're just in the right position,

and it never costs them any energy.

So we have other things that help us stabilise,

like muscles and tendons,

but to make a muscle contract,

we need to spend some energy.

And therefore it tires.

It gets tired reasonably quickly.

One of the things that makes us

a very successful upright walking animal

is that we can go for fairly long periods of time

with those muscles working,

but eventually it's going to tire.

When it tires or they're unavailable or we get surprised,

then these ligaments are the things that hold the bones together.

We know they're not perfect,

because when our foot gets into a really weird position,

these can be the things that break,

-when you sprain an ankle, for example.

-Exactly, yeah.

If you go over on your ankle, that's what you tear.

Sometimes. You can have more superficial injuries,

or less serious ones,

but the really, really severe ones are when these things break.

That's not a good situation for these joints.

'Our ligaments are vital to holding

'the architecture of our foot together.

'And as Quentin works towards the end of our dissection,

'I'm going to see how our feet perform

'when we push them to the extreme.'

PIANO MUSIC

Eve Mutso is a soloist with Scottish Ballet.

-It is quite incredible.

-Thank you!

-When did you start?

-I started when I was ten.

-Ten.

Before that, I did gymnastics, which helped,

I think, to develop the suppleness of the foot.

But with the ballet, I started when I was ten.

Every part of the foot we've seen in our dissection

is working to its very limits.

Together, they are an amazing natural machine,

tuned to perfection.

If you looked at the power behind the calf,

you can see how it's pulling her heels up

in such an extreme and remarkable fashion

so that she's able to go onto the one toe.

You can see the definition of the muscle at the back of the calf there.

At the same time, you can see how the ankle

has been bent forward in, again,

an almost superhuman fashion.

All that force has to go right down

through the foot bones,

right through the toes, in a straight line, virtually.

The foot bones are now strung

together by the powerful ligaments,

the smaller muscles of the foot,

into this incredible arched structure,

which is bearing the weight

and transferring it to the floor through a very small surface area.

She's virtually standing on her toes

at the moment, as you can see.

To make it even more complex,

she is now able to twirl around doing her pirouette,

which, again, for me, represents something so remarkable

from a biomechanical perspective.

Is Eve's foot inherently stronger than mine?

Is it more flexible, obviously more flexible, than mine?

But I mean, surely, there's a compromise,

a trade-off between being flexible and being strong.

Well, that is the remarkable trade-off

that Eve's managed to achieve.

That can only come by years and years of training

and getting the muscle to do what you want it to do,

getting the joints moving in such an unnatural position,

yet being able to hold that in a rigid and sturdy fashion.

This remarkable natural engineering allows Eve to achieve

extraordinary things with her feet,

but it comes at a price.

I've had several operations,

but I guess you just have to deal with those.

And also...

Yeah, I think just coming back from injuries,

it's when you realise that you love your profession

and you work around them.

Well, Eve, thank you very much.

I feel like a completely clumsy elephant in comparison.

The ballerina en pointe is, to my mind,

the pinnacle of what the human foot can achieve.

The entire weight of a human body

balanced on one small part of the foot - the big toe.

This is the final key structure within the foot

we haven't yet examined,

and the dissecting team are ready to reveal it.

So, George, we are now at the grand finale

in a sequence of wondrous events.

The big toe - the big boy of the front of the foot,

a truly remarkable structure for a variety of reasons.

The amount of force that goes

through that part of the foot

is absolutely enormous.

If you can picture that for any movement of the body to occur,

the final thrust must come off at the big toe level.

So your heel hits the ground first,

your foot is landing flat,

and then all of the weight

is transferred onto the front of the foot

and most of this weight is carried by the big toe.

So running down the length of the foot here is the big tendon

that goes and powers this really important big toe.

What's really impressive, and makes this a perfect driver of the body,

is that if we follow the tendon all the way back up,

it runs through the entire length of the foot.

It goes underneath your ankle

and then all the way up into the back of your leg

and when this guy contracts, it's always in the perfect position

to pull this tendon and power the body forward through the big toe.

It's the only muscle at the back here

which is perfectly aligned with the big toe,

no matter what position your foot is in.

And you can transfer your entire body weight

right down your leg, right down your foot

and out the end of your big toe.

And it's all taken on that.

Well, it is actually the end

of a long chain of energy-efficient mechanisms,

mechanisms that store and transfer energy,

mechanisms that convert that energy into activity,

so that you are able to walk in a smooth and efficient manner,

you are able to run in a smooth and efficient manner.

I can see that you really love the big toe.

I love the big toe because it is the final sequence in a box of tricks

that nature has provided for us in our feet.

Our dissection has revealed the intricate structures

within the human foot.

We've seen how the muscles and tendons,

ligaments and bones all combine to form

an incredibly sophisticated machine

that allows us to stand and walk.

But this ability is about more than just mechanics.

There's one final role that our feet play.

It's a process that starts from our earliest years.

We can't walk from birth - we need to learn how to do it.

Most of us take the ability to walk upright for granted,

but when you think about it, it is quite incredible -

all our weight balancing on two small points.

So how do we perform that balancing act on a day-to-day basis?

Here at Manchester Metropolitan University,

a group of scientists are trying to answer that question.

-Your lab, this is it.

-Yes, this is the lab.

-It's like an aircraft hangar.

-Well, yes.

Professor Ian Loram studies how we control movement,

and he's something of an expert on balance.

So, Ian, what are the factors that are involved

in us actually standing upright?

OK, well, you've got vision, which really tells you

the orientation of all the buildings and those vertical lines around you.

You've got your vestibular apparatus,

which is really that thing in your inner ear,

which tells you how your head is orientated

or whether it's accelerating and rotating.

And then you have this thing called proprioception.

Now, that's the sense whereby I can shut my eyes

and touch my nose, or even harder, touch my fingers together,

without actually seeing them.

Absolutely, so, even with your eyes closed,

that just gives you that sense

of where all the parts of your body are in relation to each other.

Proprioception is a vital sense.

How it works is that our muscles

are constantly sending electrical signals to our brain

telling it their precise position.

This stream of information helps our brain understand

which way is up and down,

and where all the parts of our body are in relation to each other.

To investigate just how important proprioception is to our balance,

Ian has designed an experiment.

And he's about to try it out on me.

Well, this is the first time I've ever shaved my legs.

All I have to do in the experiment is stand up.

OK, George, I'm now going to blindfold you.

Even with a blindfold on, it's simple,

because with every tiny movement they make,

my muscles are constantly sending signals to my brain.

And my brain uses this information to tell me

where my body is in relation to the ground.

Well, I mean, that's fine, I can walk around.

I can stay upright. It's fairly easy.

I'm relying on my proprioception,

but Ian has found a way to stop it working.

OK, George, what we're now going to do is test your balance.

We're going to ask you to control the motion of the board

with your muscles,

which will make the board go forwards and backwards.

Three, two, one...

Now I'm standing on a moveable board.

My feet have no connection with solid ground.

Every time they move, the board moves too,

and the signals they send to my brain are confusing.

Oh, I-I couldn't control that at all.

Because my muscles aren't moving in relation to a fixed point,

my brain can't build up an accurate picture of the world around me.

That's impossible. I'm really unsure which way is up.

I'm amazed by how disorientated I feel

without the ground beneath my feet.

And it shows me my feet are playing a role

that I was never conscious of before.

When you're on the ground, your ankles are rotating,

and that signals the stretching information to the brain,

and your brain uses that information

to control the muscles and keep you in balance.

So when I was on the shelf that moved with the machine,

my ankles were effectively locked? I wasn't getting any information?

Absolutely, so, really,

you were deprived of that sensory information.

So what allows us to balance is a crucial interaction

between our foot and leg muscles and our brain.

Some muscles provide the brain with information,

and the brain then tells particular muscles to tense or relax.

But there are occasions when this communication breaks down,

and the results can be dramatic.

Right, Ian, what now?

Ian illustrates this with a second experiment

that's as deceptively easy as the first -

walk across a plank about six inches wide.

But Ian then reveals the hard part.

Oh!

Ah!

I know this is just as easy

as it was on the floor,

but I'm now...

I don't want to move my legs.

Oh!

Whoa...

I'm... Oh, Jesus!

Oh!

Most of us have had this feeling -

something that is simple in one situation

suddenly becomes incredibly difficult.

Ian, why did I find that so hard?

-Yeah, you obviously were afraid.

-Yes.

-That's a very sane response.

But the thing is, your muscles were tensing up,

and that was distorting the proprioceptive information

coming back into your brain, and that was affecting your balance.

So, of course, that made you tense up even more.

So you have this possibility of a vicious cycle developing.

This vicious cycle helps explain

why my balance was so poor on the plank.

Fear of falling made my muscles tense

and this interfered with the crucial information

they were providing to my brain.

A psychological fear has produced a very real physical response.

I'm frozen again.

So this proprioceptive sense is really important.

Yeah, proprioception is measuring these minute changes all the time

and feeding that information into the brain.

The brain uses that information to contract the muscles

and that interaction is maintaining balance.

And it's what makes us able to actually stand upright.

Yes, and I still find it so amazing that, standing still,

all this is going on all the time and we barely realise it.

So even standing still, the muscles in our foot and calf

are making constant minute changes

just to keep us upright.

And as they do this, those muscles provide our brain

with essential information to help us balance.

Our feet really are remarkable.

They're sensitive enough to gather information

about the world around us

and yet strong enough to bear all that weight pressing down on them.

Yet we're hardly even aware of the complex interactions

that go on between our feet and our brain

that allow us to perform the everyday act of walking.

Most of us take thousands of steps every day.

And every step is possible only thanks

to the elegant and intricate mechanisms within our feet.

I've been astonished by the complex interplay

between all the different parts of the foot

coming together that allow us to walk, run and jump.

Our dissections of a human hand and foot

have revealed the natural engineering

that allows us to perform tasks we take for granted.

Dissecting a hand, I saw the intricate machinery

that gives us a unique combination of power and precision.

And in our foot dissection, I've seen the complex mechanisms

that allow our feet to be so adaptable -

the outer layers that combine protection and sensitivity,

muscles that provide balance and power...

..ligaments that allow our feet to be both flexible and rigid...

..and I've seen the ingenious structures that recycle energy

with every single step we take.

Dissecting hands and feet,

I've certainly gained a new respect for the extremities of my limbs

and they've caused me to think again about what it is to be human.