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  • - [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.