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Why don't humans walk like THAT? - Video học tiếng Anh
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Why don't humans walk like THAT?
Why don't humans walk like THAT?
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자막 (48)
0:00
- Why don't people walk like this?
0:03
And instead, we have our arms swing with the opposite leg.
0:06
I mean, why do we move our arms at all,
0:08
using all that extra energy
0:09
instead of just letting our legs do it on their own?
0:11
Initially, some scientists thought
0:12
that we just inherited this way
0:13
of walking from our ancestors who walked on four limbs.
0:17
But quadripeds actually swing their limbs
0:19
in a lot of different ways.
0:20
They can lift just one limb off the ground
0:22
if they're walking slowly.
0:24
Horses will have diagonal pairs swing together,
0:26
and camels often move their same side limbs together
0:29
and cheetahs go so fast sometimes none of their limbs
0:32
are touching the ground.
0:33
And for us, it seems like arm swinging
0:35
might be one of our secrets for becoming the two-legged ape.
0:38
When your leg does this,
0:40
your upper body slightly rotates this way,
0:43
so swinging your arm the other way,
0:45
even slightly, counteracts that rotational push on your body
0:48
and a twisting force on your foot.
0:50
And this changes according to how fast you're walking,
0:52
of course.
0:53
When you stroll,
0:54
your arms don't always need to stay in sync
0:56
because the rotational forces aren't very big.
0:59
But when you move faster, your arms want to sync up
1:01
to counteract that stronger rotation.
1:04
Now, this is a small energy benefit,
1:06
but it can really add up.
1:07
Weirdly, it seems like it actually takes our body
1:10
less energy to swing our arms, not more.
1:13
When we're going slow, our arms counteract the forces
1:16
by just swinging free like pendulums.
1:18
So not much effort there.
1:20
But some scientists found that when we go fast,
1:22
we actually use 12% less energy when we swing our arms
1:26
versus holding them still
1:27
because the arm swinging keeps us from wasting energy
1:30
on balance and uses it to propel us forward instead.
1:33
And according to that experiment,
1:35
when people run like an idiot like me,
1:37
they consumed about 25% more energy.
1:40
Now this is why race walkers look like this
1:42
and not like this.
1:45
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