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This is Eliud Kipchoge.

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On October 12, 2019, he ran a marathon in
under 2 hours, a barrier no human had been

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able to break in the preceding 13.8 billion
years—and these are the Nike Vaporflys.

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They also ran a marathon in under two hours—and,
coincidence alert, it just so happens they

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did it whilst strapped onto Eliud Kipchoge’s
feet.

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And because we can never once just enjoy something,
the question of how much of that 1 hour, 59

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minute and forty-second marathon can be credited
to this guy, versus how much can be credited

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to these guys, quickly became a subject of
enormous controversy—so much so that some

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versions of the Vaporfly have now been declared
illegal in competition.

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The modern running shoe dates back to 1865.

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They looked like this, and while they were
very good at looking like a vampire’s house

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slippers, they were not very good at helping
people run fast.

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In time, running shoes evolved—1917 saw
the advent of rubber soles, in 1972 Nike introduced

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the famous waffle sole, and in 2020 Mizuno
made whatever this is.

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Over this period, running shoes basically
standardized into three parts: the upper,

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the midsole, and the outsole.

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The upper is this part—it’s designed to
be light and basically just keep the shoe

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on your foot.

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The outsole is this part—it makes contact
with the ground, providing traction and durability.

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People used to care a lot about outsoles,
but these days, outsoles are out.

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What’s in?

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Midsoles.

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The midsole is typically made of some type
of foam, and provides cushioning for the runner’s

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foot.

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The key to a great midsole is energy return:
how much of the energy the runner expends

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when pushing the midsole down is returned
when the midsole bounces back up?

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Most modern shoes return around 50-65% of
energy back to the runner.

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The Nike Vaporflys return about 85%.

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So, what makes the Vaporflys so good?

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Well, let’s go deeper into energy return.

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Energy return comes from a combination of
compliance and resilience—which coincidentally

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are also the two traits I look for in my unpaid
interns.

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In physics, compliance is how much something
will give when you put pressure on it.

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Resilience is how much of the pressure absorbed
will be returned back.

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For example, sand is very compliant, but not
very resilient: if you find yourself running

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in sand, either as part of an inspirational
montage or a perspirational worm-chase, you’ll

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find it’s difficult, because while the sand
gives a lot beneath your feet, it doesn’t

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return the energy back to you.

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A steel plate, on the other hand, is very
resilient but not very compliant—however

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far you press it down, it’ll return back
up…but it’s really hard to compress steel.

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Nike’s Vaporflys provide unmatched energy
return by striking a perfect balance of compliance

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and resilience, thanks to two key innovations.

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The first is this: Pebax foam, which Nike
gave the name “ZoomX foam,” because Pebax

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sounds like a decongestant and ZoomX sounds
cool as hell.

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For a long time, midsole foam in running shoes
was kept thin to reduce weight—but Pebax

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foam is so light that Nike was able to justify
a much thicker midsole—in the case of the

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Vaporflys, 40mm.

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The other key to the Vaporflys is this: a
super-resilient carbon fiber plate that runs

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the whole length of the shoe.

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Combined, the thick foam and sturdy plate
strike a perfect balance between compliance

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and resilience: Vaporflys have been shown
to improve a runner’s overall efficiency

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by 4%.

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Now for some things, like a Rotten Tomatoes
score or the retention on this video, a 4%

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change may not matter all that much, but in
running, it’s huge.

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In the 2016 Olympic marathon, 4% was the difference
between first place and 15th place.

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The top three finishers in that 2016 Olympic
marathon, by the way, were all wearing Nike

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Vaporflys.

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That’s because Nike secretly launched the
Vaporflys at those Olympics, which, depending

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on who you ask, was either an incredible Don-Draper-level-genius
marketing move, or it was cheating.

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If you ask the cheating camp, they’ll say
that sports should be about humans competing

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against each other based on athletic ability—not
based on who has the fanciest gear.

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And it started to seem like in order to win
a race, Vaporflys weren’t just an asset—they

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were a necessity.

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In fact, some athletes sponsored by other
shoe companies have been caught racing in

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Vaporflys with the logo Sharpied out.

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That’s how much better they are.

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Until 2020, the rules from IAAF, the international
governing body for track, were simple: “Shoes

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must not be constructed so as to give athletes
any unfair advantage or assistance.”

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So the question was: are the Vaporflys an
unfair advantage?

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This question, of so-called “technological
doping,” is not a new issue.

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Remember the 2008 Olympics, when all the swimmers
wore those weird bodysuit things that made

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them look like they were about to lose the
Hunger Games?

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They were called LZR racers, and in 2008,
swimmers wearing them won 98% of Olympic swimming

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medals, and broke 17 world records, leading
FINA to ban body-length suits.

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On January 31st, 2020, World Athletics announced
a highly-anticipated rule change, limiting

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midsole thickness to a maximum of 40mm, and
allowing for no more than one stiff plate

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in a midsole.

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While this ruling made certain Vaporfly prototypes
illegal—including the sprinter-specific

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Viperfly, and a three-carbon-plated version
of the Alphafly—by and large, it was a win

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for Nike, whose core Vaporfly products remained
legal, meaning that come Paris 2024, anyone

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who wants a medal had better either get a
Nike sponsorship, or a Sharpie.

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Speaking of sponsorships, I’m incredibly
excited for this one, because I’ve got a

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new series out that’s a dual-release on
CuriosityStream and Nebula called Extremities,

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where I explore how and why the world’s
most remote settlements exist.

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What’s cool about my new series Extremities
is that it isn’t new at all: Extremities

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was a podcast and then a YouTube channel,
but it was always too expensive to produce

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for it to be profitable.

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But thanks to CuriosityStream and Nebula,
we have finally been able to finally make

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the version of Extremities we always dreamed
of—with incredible footage, super high-quality

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motion graphics, and the time to do a ton
of interviews and research.

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Once you’ve watched Extremities, you can
check out other Nebula-exclusive content:

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Half as Interesting’s Crime Spree series,
the HAI bricks special, our three-part trivia

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show, Wendover documentaries, Tom Scott’s
Money, Real Life Lore’s Modern conflict

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series, and so much more.

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Weirdly, the best way to get Nebula—which
by the way is the creator-owned streaming

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site I started with a ton of other educational
YouTubers—is with the CuriosityStream-Nebula

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bundle.

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For weird budget and marketing reasons, it’s
actually cheaper to buy the bundle deal and

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get access to both CuriosityStream and Nebula
than to buy either individually—only about

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$1 a month.

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CuriosityStream, in addition to being home
to Extremities, also has a ton of other incredible

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documentary content, including the great Boston,
about the Boston Marathon.

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So get the bundle deal, for about $1 a month
if you pay annually, at curiositystream.com/HAI,

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and check out my new series Extremities.