- [Adrienne] Cheetahs can reach up to 70 miles an hour
in just three seconds.
- [Dr. Raynor] If you were to look
at the actual speed that a human
being could run, you're probably looking
at 30 kilometers an hour,
but only for a very short period of time.
- [Synthesized Voice] But why is that?
Cheetahs, humans, what's the difference?
[curious music]
[lights clack]
I am a computer.
What is human?
Is human cheetah?
[curious music]
[computer chimes]
- The cheetah is able to run up to 70 miles an hour.
And everything about their physiology
and their body is designed
for them to reach very quick speeds
in a very short period of time.
I think one of the most unique aspects
of the cheetah is the fact that
about 50% of their entire body mass is made of muscle.
- And the type of fibers that a cheetah has compared
to the type of muscle fibers that we have are much
more heavily weighted towards fast twitch fibers
and they are better able to contract
at a much more quick pace.
- Over 80% of the musculature in the thigh
or the top of the back leg
in the cheetah is made
up of these fast twitch muscle fibers.
That's an enormously large proportion of that muscle type,
which is what enables them to reach amazingly fast speeds.
Cheetahs have a very large psoas muscle
which is what helps extend out the hip and then pull it back
into the body very quickly and powerfully.
And that extension and flexion is what enables them
to push off very strongly
with their back legs and generate that power.
Take a look at this video of this cheetah running
at high speed.
Watch as the cheetah is sprinting.
Those hind legs extend out
and are pulled back very quickly and very powerfully.
And you can see that spine flex.
When the cheetah is in full stride,
you can see that everything about it
is built for being aerodynamic.
Even the ears are pulled back against the head,
cutting down on any wind friction.
Another thing to note,
they actually have a four beaded gate, very similar
to a horse when it is galloping, but unlike other species
the cheetah has two moments in its stride
when all four feet are off the ground at the same time.
[computer chimes]
If you think about the difference
between a flat-footed walk and almost a tiptoe walk
the cheetah has some unique musculature whereby
it can be ready for action,
ready to start that sprint almost on the spur of the moment
- When you're trying to run at speed,
we are really only hitting or striking the ground
with the ball of the foot and the toes.
The reason why we are doing this is
because we are trying to employ the foot
as an additional lever
with which to propel ourselves forward.
Take a look at this.
We have a lever from the hip to the knee.
We have another lever from the knee to the ankle.
We have a third lever
from the ankle to the ball of the foot.
And the last lever is from the ball of the foot to the toes.
This allows us to use the muscles of the foot
and of the lower leg from the calf downwards
to generate power when the foot is contacting the ground.
- So let's take a look at a cheetah foot.
So not much of the bottom of the cheetah foot,
the actual bones of the cheetah foot
are in touch with the ground.
The nails are always extended,
acting like those track cleats when the animal sprints.
You can see there's only four toes here,
the middle two toes are the most weightbearing.
So they take the brunt of all of the cheetahs weight.
You may wonder what happened to the fifth toe.
That is actually what we know as the dewclaw.
That is what they use to trip up their prey
when they're chasing after it.
As they reach the back legs of their prey,
they hook those back legs with that dewclaw
causing the animal to trip and stumble
and then they can jump in and finish the kill.
So you'll notice when the cheetah is sprinting
after its prey, it doesn't go in a straight line.
The prey is trying to get away from the cat.
And so it makes a zigzag motion when it's running.
It gets very close to the ground,
almost touching its side to the ground,
and it's able to do that because those nails,
those claws on its feet are helping to give it a lot
of traction and stability.
[computer chimes]
The cheetah's breastbone isn't well attached
to the rest of their musculature.
They call it a free floating breastbone.
- They have a chest cavity
which allows a much larger expansion of space
that's available to expand the lungs.
- And that actually enables them to have a lot
of flexibility in the front.
And to really stretch out that stride
when they're sprinting.
- Humans don't do that because we are tuned
to be generalists and do lots of things.
Human respiration when you're exercising can go anywhere
from 20 to 24 probably even higher at maximum capacity.
- When a cheetah sprints, they have a respiration rate
of around 150 breaths per minute.
[computer chimes]
Cheetahs disperse heat in several different ways.
Their body temperature goes up so much
when they're doing those very quick, fast sprints.
- For human beings, we are fortunate to have a number
of ways in which we can dissipate heat.
The easiest to think about is through perspiration.
When we are generating heat,
we can start to sweat and the movement
of air across the water that's on the surface
of the skin will allow us to cool ourselves down.
- Cheetahs can release heat
through their mouth and even through their feet.
- Another mechanism that we have for dissipating heat is
through the hairs on the surface of our skin.
When we're trying to retain heat, the hairs
on our arms will stand up in order to slow the movement
of air across the surface of the skin.
When we are trying to dissipate heat,
we will make sure that those hairs all lay flat so
that we can lose as much heat to the moving air as possible.
- The black spots
on the cheetah are thought to also help disperse heat.
The hairs of the black spots are actually longer
than the hairs that are the yellowish to orange color.
So those longer hairs are thought to help disperse
and release the heat.
- The last mechanism that we can use
to dissipate heat is through our respiration itself.
When our core temperature increases,
the air on the inside of us will also
be increased in temperature.
And as we expire that warm air
we will inspire cool air coming in,
which allows us to disperse heat through that mechanism.
- And cheetahs are of course,
able to pant like you see dogs and cats do sometimes.
They have to decrease their body temperature
before they can consume their kill.
[computer chimes]
The cheetah has a very flexible spine,
which enables it to move quickly,
especially to zig-zag when it's chasing prey.
- When it comes to sprinting,
flexibility is something that's quite important.
Take a look at this video of a human sprinting.
This is your stride length.
And our goal is to maximize that stride length
when we are moving through space.
The way that we do this is by increasing the flexibility
of the hip, knee and the ankle joints
in order to cover ground as quickly as possible.
- The cheetah also has a very heavily muscled back
which helps that spine extend and flex
so that they can stretch out when they're sprinting
and really gain those long strides.
[computer chimes]
The cheetah tail is about 50% of the length
of the entire rest of the structure.
So it's very long in proportion
to the entire animal and that tail acts as a rudder.
So it helps it steer
around sharp corners when there's zigzagging
and chasing after their prey,
it's also a very muscular tail.
And so that helps as a counterbalance
or a counterweight so that they don't lose their balance
as they're sprinting and turning quickly.
[computer chimes]
So let's take a look at a cheetah's skull.
So the cheetah skull is very rounded and concave
across the top, and that helps it be very aerodynamic,
just like the rest of its body.
- The human skull on the other hand is not designed
for a specific purpose, but it is designed to
allow us to be good at a number of different things.
There's a couple of things that are unique
about the human skull.
One of the most obvious things is the size
of the cranial vault, which holds your brain
and relative to other animals,
you'll find that the cranial vault for humans
is quite large,
and this is because our brains are quite large.
- [Woman] Cheetahs have really large eye sockets
and they're true predators.
Those eyes are faced forward scanning all the time
for potential prey.
- 'Cause we are bipedal animals.
We are able to see a much further distance
because of our point of perspective.
- Cheetahs also have teeth designed
for tearing muscle meat very quickly and ingesting as much
as possible in a very short period of time.
They're called bolters.
They actually bolt their meat.
They can eat up to 10 to 15 pounds of food at a time.
And to be able to consume up to 15%
of their body mass in food is an amazing
amount of food that they can eat all at one time.
[computer chimes]
- In order for humans to run as fast as a cheetah,
this is how they would have to change.
I would want to make sure that the muscles on both the front
and the back of the thigh were as large as possible.
I would want to shorten the length from the hip to the knee,
but I would probably lengthen the lever from the knee down.
I would make the foot so that the heel of the foot
was suspended in the air.
We could end up having claws
to propel ourselves much more efficiently
every time that we contact the ground.
I would also want to make sure that the muscles
of the shoulders and upper chest were quite large
with the floating breast bone in the front in order to
increase the turnover.
Those are some of the things that I would do to
create the ideal sprinting human.
- [Synthesized Voice] I Understand.
A cheetah is not human.
[printer whirring]