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02/07/2020    Kevin A. Kirby, DPM

NJ Podiatrist Comments on Nike Vaporfly 4% Flyknit Shoes

The big story about the Nike Vaporfly 4%
running shoes are not its upper material.
Rather, it is the revolutionary combination of
a compliant, resilient, and lightweight midsole
foam along with a carbon-fiber plate embedded
within that midsole foam that makes the Nike
Vaporfly shoe so special.

The name “Vaporfly 4%” came about since Nike’s
own research by Hoogkamer et al, published in
2018, showed their shoe reduced the energetic
cost of running in all 18 subjects tested, with
the Vaporfly 4% shoe being about 4% more energy
efficient compared to two other popular
marathon racing shoes, the Adidas Adios BOOST
2, and the Nike Zoom Streak 6 (Hoogkamer W et
al: A comparison of the energetic cost of
running in marathon racing shoes. Sports
Medicine, 48:1009-1019, 2018).

The Nike Vaporfly 4%, and its newer model, the
Nike Vaporfly Next%, both have a full-length
carbon-fiber plates that are embedded within
the midsole of the shoe. However, the most
important feature that has made the Vaporfly
more energetically efficient for runners is a
new, more compliant, and resilient midsole
foam, called polyether block amide, or "Pebax"
foam. In their mechanical testing of shoe
midsoles, Hoogkamer et al (2018) found that the
Pebax foam of the Vaporfly shoes returned
nearly double the amount of energy to the
runner than the two other popular marathon
racing shoes tested.

In addition, the Nike Vaporfly 4% and Next%
both have very thick midsoles which are ultra-
lightweight which has allows these unique shoes
to presumably store and more release more
energy with each running step than other
marathon racing shoes, being 40% thicker than
other comparable marathon racing shoes.
Without this thicker midsole, it is likely that
the Nike Vaporfly models would not be able
produce the same performance-enhancing effects
that they have shown in elite marathon racers
over the past 3 years it has been available to
runners. This knowledge that shoe sole
thickness helps determine the energy return
potential of a running shoe, as long was shoe
mass is kept to a minimum, is important when
considering the recent ruling from World
Athletics, published on January 31, 2020, which
now bans running shoes from having a sole which
is greater than 40 mm in thickness

The Nike Vaporfly 4% and Next% are not just
cool new running shoes. These shoes now
currently hold the top five marathon times in
the world. The Nike Vaporfly running shoe, by
itself, has totally changed racing events in
distance running to the point of where we are
asking, was it the shoe, or the athlete, that
allowed that record-breaking marathon

Kevin A. Kirby, DPM, Sacramento, CA

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