20/02/2022
The Nike Vaporfly: The Shoe That Forever Changed Distance Racing
[I wrote this article for my March 2020 Precision Intricast newsletter. It is reprinted here with permission from Precision Intricast Orthosis Laboratory.]
The Nike Vaporfly shoe has been all over the news for the past few years, and rightfully so. The Vaporfly running shoe has, quite literally, forever changed distance running and its associated records. This revolutionary running shoe was first introduced as a prototype by Nike at the Rio Olympics in August 2016, where it was worn by the top three marathon finishers in the men’s marathon.
The first version of the Vaporfly hit the consumer market in July 2017 as the Nike Zoom Vaporfly 4% (NV4).
The name “Vaporfly 4%” came about since Nike’s own research had found that their new shoe reduced the energetic cost of running by about 4%. In Nike’s research, 18 high-caliber athletes ran six 5-minute trials on a treadmill in three racing shoes, the Vaporfly prototype (VF), the Adidas Adios BOOST 2 (AB), and the Nike Zoom Streak 6 (NS). Each subject ran three sessions at speeds of 14 km/h (6:54 min/mile), 16 km/h (6:02 min/mile) and 18 km/h (5:21 min/mile). Oxygen uptake was measured for all the runners to determine the energetic cost of running. The research showed that the VF shoe reduced the energetic cost of running in all 18 subjects tested, with the VF shoe being 4.16% more energy efficient than the NS shoe and 4.01% more energy efficient than the AB shoe, thus the name Vaporfly 4% (Hoogkamer W et al: A comparison of the energetic cost of running in marathon racing shoes. Sports Medicine, 48:1009-1019, 2018).
The NV4 has many special features within it that makes it such a fast shoe to run in. One of its features is a full-length carbon-fiber plate that is embedded within the midsole of the shoe that is wrongly thought by many to be the most important performance-enhancing feature of the NV4 shoe. However, the most important feature that has made the NV4 more energetically efficient is the new foam that is used within its midsole called polyether block amide, or PEBA. In their mechanical testing of shoe midsoles, Hoogkamer et al found that the PEBA foam of the NV4 shoes returned 7.46 Joules (J) of mechanical energy per running step versus 3.38 J seen in the ethylene vinyl acetate (EVA) foam used in the midsole of the NS shoe and versus the 3.56 J of mechanical energy return for the thermoplastic polyurethane (TPU) or “Boost” foam of the AB shoe midsole (Hoogkamer et al, 2018).
The reason the PEBA foam is so special, allowing the NV4 shoe to be unlike any other shoe in its ability to return energy to the runner, is that the PEBA foam is exceptionally lightweight (i.e. low density), compliant, and resilient, more so than any other midsole foam that has ever been used within a running shoe. More compliant midsole foams will deform (i.e. compress) more for a given force applied to it. Resilience, on the other hand, is the percent of the stored mechanical energy that is returned to the runner after the midsole has been first compressed, and then released back to its original shape.
The mechanical testing by Hoogkamer et al on the shoe soles, using an impact force of 450 pounds for 185 milliseconds, showed that the NV4 foam was about two times more compliant than the NS or AB midsole foams, deforming, respectively, 11.9 mm versus 6.1 and 5.9 mm. The NV4 foam also stored more mechanical energy (i.e. more resilient) that the NS or AB midsole forms, with the NV4’s PEBA foam returning 87.0% of the energy versus 75.9% for the AB shoe and 65.5% energy return for the NS shoe (Hoogkamer et al, 2018).
This difference in compliance and resilience between the NV4 shoe and the other tested marathon racing shoes was magnified by the greatly increased midsole thickness of the NV4 shoe. The NV4 midsole was 31 mm thick at the rearfoot, while the NS and AB shoes only had a 23 mm thick rearfoot midsole. The forefoot of the NV4 shoe was also thicker than the other shoes, with the NV4 shoe having a 21 mm thick forefoot midsole, while the NS shoe had only a 15 mm thick and the AB shoe had only a 13 mm thick midsole thickness at the forefoot (Hoogkamer et al, 2018).
In other words, without the thicker layer of midsole foam, being, on average, 40% thicker than the midsoles of the NS and AB shoes, the NV4 shoe could not have returned near as much energy to the runner with each step as it did. This knowledge becomes very important when trying to understand the biomechanical reasoning behind the 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.
https://www.worldathletics.org/.../modified-rules-shoes).
After the Nike VF4 shoe started to break records in distance races, Nike then brought to market their newest version of their Vaporfly shoe, the Nike’s Vaporfly Next% (VN%) in April 2019. Upgrades to the VN% shoe included a lighter-weight upper, a less-slippery sole, and 15% more PEBA foam in the shoe midsole, giving the VN% shoe a sole which is thicker than any other racing shoe currently available. Because of their very thick layer of highly compliant and highly resilient foam, its carbon-fiber plate embedded within the shoe midsole, and its light weight (being amazingly light for a shoe with such a large, voluminous midsole), the Nike VF4 and VN% shoes have literally helped rewrite the record books for distance running over the past two and a half years.
For example, Eliud Kipchoge, from Kenya, wearing a version of the Nike VN%, set the world marathon record in a time of 2:01.39 while winning the Berlin marathon in 2018. Kipchoge’s 78-second improvement on the existing marathon record was the largest improvement in the marathon over the past 50 years. Another Kenyan, Brigid Kosgei, broke Paula Radcliffe’s women’s world marathon record at the Chicago marathon in 2019, in the Nike VN% shoes, reducing the women’s marathon mark by an amazing 81 seconds from Radcliffe’s 2:15:25 to 2:14.04.
In addition, Joshua Cheptegei of Uganda set a new road 10K world record of 26:38 on December 2019 at the 10K Valencia Trinidad Alfonso in Valencia, Spain, while running in the Nike Vaporfly Next% shoe. The five fastest marathon times which have ever been recorded were run in a version of the Nike Vaporfly shoe. Yes, the Nike Vaporfly 4% and Next% are shoes that have forever changed distance racing by enhancing the performance of runners.
However, now, when a new distance running record is broken, will we ask, “Was it the athlete, or was it the shoe that broke the record?”
