42 km is the distance that Pheidippides ran in 490 B.C. from Marathon to Athens to bring the news of victory against the Persians (Figure 1). According to the legend, once arrived in Athens, Pheidippides managed to scream “Nenikékamen!” (“We won!”), before dying due to the effort.
The marathon is the most legendary race of the sports world and the secret dream of every single runner, becoming day after day the ultimate challenge for the majority of them.
The first modern marathon was introduced during the Olympic Games of Athens in 1896 by Michel Brèal, a friend of the founder of the modern Olympic Games, Pierre de Coubertin.
Since then, the marathon world record has decreased by almost one hour and a half. At the time of writing this article, the record holders are Eliud Kipchoge with 2 hours, 1 minute and 39 seconds among men (Berlin marathon, 2018) and Brigid Kosgei with 2 hours, 14 minutes and 4 seconds among women (Chicago marathon, 2019).
Break the record!
The continuous desire of breaking the human limits pushed Nike firstly and then INEOS to sponsor the projects Breaking2 and INEOS 1:59 Challenge, respectively, with the goal of beating the two-hour limit. On his first attempt in Monza (Italy) in 2017, Eliud Kipchoge could not break the record by a mere 25 seconds. But on his second attempt in Vienna in 2019, he managed to run the 42.195 km in a record one hour, 59 minutes and 40 seconds (Figure 2).
Despite the impressive performance by the Kenyan runner, the record was not officially recognized by the IAAF (International Association of Athletics Federations) due to its not being part of an official competition. Besides, different adaptations were observed during the attempt, starting from having different pacemakers who ran in and out of the competition, running at a low altitude route and in a V-shape formation.
But Kipchoge had another secret weapon for breaking the record: newly designed shoes that included carbon plates and super soft foam.
Newly designed shoes specific for marathon running
The design of athletic shoes depends on the different requirements of each sport. Running shoes are light and flexible, but for each distance or kind of terrain, their characteristics change.
The choice of marathon racing shoes influences the performance of the athlete . For this reason, Nike designed the Alphafly expressly to break the sub-two (hours) record in the marathon, using different characteristics and materials from those of the other running shoes available on the market (Figure 3).
Nike submitted the patent of the Alphafly shoes in the U.S. Patent Office. In the patent, there are different variations of the sole. But in general, the characteristics of the Alphafly (and of the connected series shoes as Vaporfly)  allow them to be the lightest shoes on the market . The common characteristics are:
- the full-length carbon-fibre plate embedded in the midsole (Figure 4)
- the very lightweight ZoomX midsole cushioning
- the cushioning pods
New materials for high-performance shoes
Generally, all the running shoes have a midsole made of foam materials, able to cushion the impact, store and release part of the mechanical energy. All the foams are viscoelastic and can release more energy, depending on the compliance of the material. The midsole of the Alphafly (and of the shoes of the series) comprises four different levels that permit the maximization of the energy-returning (Figure 4):
- a top layer of foam
- the second layer of composite material
- a third carbon plate layer, and a bottom layer of more foam.
The fabric of the shoe itself, called “Vaporweave”, is highly waterproof, absorbing only 7% of humidity and water. A dryer fabric means a lighter shoe and, consequently, less weight to move during each step, which saves more energy. The material is designed specifically by Nike as a combination of two thermoplastic materials, TPE (thermoplastic elastomers) and TPU (thermoplastic polyurethanes), which add resistance, elasticity, transparency and high thermal properties.
The foam present in the Alphafly shoes’ midsole (called ZoomX) was initially designed for aerospace applications. The original name of the material is Pebax®, a family of polyether block amides (PEBA). This thermoplastic elastomer is obtained by polycondensation of a carboxylic acid polyamide with an alcohol-terminated polyether.
Having a low density and superior mechanical and dynamic properties (flexibility, energy return and fatigue resistance), it is the perfect element for constituting the midsole of running shoes.
As a consequence, it has been shown that in the Vaporfly 4%, the ZoomX foam is able to return 87% of the energy stored during the impact, as compared to 76% and 66% of that by its counterparts, which are usually in ethylene vinyl-acetate foam .
By using a newly designed lighter upper material, Nike was able to add more of its bouncy ZoomX foam in the Vaporfly NEXT% without changing the shoe’s overall weight.
Finally, the foam was shaped to create a wider fore sole, while the rear part had a particular “winged” shape in order to increase the aerodynamics (I personally would compare this with the talaria, the winged shoes of the Greek messenger god Hermes, or Mercury for the Romans. Therefore, somehow these Nike shoes can be really considered to be used only by the gods of running).
Depending on the Alphafly version, more carbon plates are inserted in the shoe to support the foam of the midsole (Figure 4).
The carbon layers (made of carbon fibres) provide stability, shape and stiffness to the foot, helping with the forward propulsion. In addition to that, the carbon plates permit the fulcrum of the push to be much further directed towards the tip of the foot, providing advantages during the propulsive phase. In the version with three carbon inserts, the plates have different sizes. The top one runs through the whole sole, while the other two only in the back part.
Aside from the different foam layers and carbon plates, different layers of cushioning pods (Zoom Air Pods) are designed to bump the strike impact and provide a greater energy return. The cushioning pods are filled with fluid or foam pressurized at 20-25 psi (138-173 kPa), and when compressed, they absorb the force of impact (Figure 5) .
The tabs on this plate are configured to act as flex points, while the notches minimize the stiffness of the plate. The second (rear) notch, in particular, allows the plate to twist and/or bend within the midfoot region (Figure 5) .
How the running mechanics change
The use of the Nike Vaporfly 4% has been shown to improve the athlete’s performance by 4% in comparison to other marathon racing shoes (thus, the 4% in the model name) .
In particular, Vaporfly brought about benefits on the biomechanics, showing different stride length, plantar flexion velocity and centre of mass oscillation. Wearing the Alphafly shoes, athletes showed greater peak vertical ground reaction forces, slower step frequencies and longer ground contact times than when running with the control shoes .
The increase of the ground contact time, in particular, reduces the oxygen uptake, making the running action more efficient [1, 4].
The Nike Vaporfly showed an increase in the running economy by 2.6% ± 1.3% compared with the Nike Zoom Matumbo, and by 4.2% ± 1.2% compared with the Adidas Adizero Adios . The material and design of the sole, in particular, that of the heel, change the muscle activation in the lower extremities, the oxygen consumption [5, 9], and how the Achilles tendon stretches, saving additional energies .
The carbon plate, in particular, does not seem to act as a spring, but rather to stabilize the ankle joint and reduce the load on the calves. At the same time, the toes remain stretched, and in this way, athletes can save the energy necessary to flex them .
Finally, a low-profile pad in the heel can prevent a runner’s heel from slipping out and reducing the pressure on the Achilles tendon. In addition, the laces are placed more laterally, allowing for the reduction of the pressure on bones and tendons, and thus, better blood flow and muscle recovery.
When the doping is wearable
The characteristics and materials of the Vaporfly that Kipchoge used during the INEOS 1:59 Challenge render the shoes illegal, as they are considered by the WADA (World Anti-Doping Agency) and IAAF as technological doping.
Technological doping is the practice of gaining a competitive advantage by using sports equipment.
It ranges from swimming suits to artificial limbs (running blades for paralympic athletes). However, in order to make them legal and available on the market, Nike proposed Alphafly within the IAAF limitations, i.e. having a sole thinner than 40 mm, for example.
These shoes are expected to be accepted during the marathon of the Olympic Games in Tokyo during the summer of 2020 (postponed to 2021). For that, however, they need to be available on the market for at least four months.
Accordingly, Nike Vaporfly will be on sale starting April 30 (for a price of $250). At the same time, other athletic shoe brands are releasing similar shoes to allow their sponsored athletes to compete with the same advantages Nike users enjoy.
“I am fascinated by how the development of new sports equipment allows pushing the boundaries of human limits further, reaching new records.”
PhD in Sport Biomechanics, Bioengineer
*This article is the work of the guest author shown above. The guest author is solely responsible for the accuracy and the legality of their content. The content of the article and the views expressed therein are solely those of this author and do not reflect the views of Matmatch or of any present or past employers, academic institutions, professional societies, or organizations the author is currently or was previously affiliated with.
 “Kenya’s Eliud Kipchoge breaks two-hour marathon barrier” DW.
 Hunter, I., McLeod, A., Valentine, D., Low, T., Ward, J., Hager, R. 2019. Running economy, mechanics, and marathon racing shoes. J Sports Sci.;37(20):2367-2373.
 “A Breakdown of the Nike Kipchoge Prototype Shoe”. Believe in the Run.
 “The Nike Air Zoom Alphafly Next % is here, and it’s legal (probably)”. Running Magazine.
 “The Nike Air Zoom Alphafly Next% Has Been Announced”. Runners World.
 Nike ZoomX Vaporfly NEXT%. Nike Running.
 Hoogkamer W, Kipp S, Frank JH, et al. A Comparison of the Energetic Cost of Running in Marathon Racing Shoes. Sports Medicine (Auckland, N.Z.). 2018 Apr;48(4):1009-1019. DOI: 10.1007/s40279-017-0811-2.
 Barnes, K.R., & Kilding, A.E. 2019. A Randomized Crossover Study Investigating the Running Economy of Highly-Trained Male and Female Distance Runners in Marathon Racing Shoes versus Track Spikes. Sports Med. Feb;49(2):331-342. doi: 10.1007/s40279-018-1012-3.
 Nigg, B.M., Stefanyshyn, D., Cole, G., Stergiou, P., Miller, J. 2003. The effect of material characteristics of shoe soles on muscle activation and energy aspects during running. J Biomech.;36(4):569-75
 “Can Nike’s New Marathon Shoes Make You Faster? A Nike-Funded Study Says Yes”. Wired.
 “The Nike Air Zoom Alphafly Next% Has Been Announced”. Runner’s World.
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