The 4% Difference: Investigating the Effect of the Nike Vaporfly 4% on Distance Running

Luke Rambo

Braun Award for Excellence in Writing in the Scott L. Carmona College of Business

Nominated by Kevin Meyer, Assistant Professor of Economics

Luke Rambo, of Marquette, Michigan, graduated in May 2022 with a bachelor of business administration in finance. Luke is working for Mercantile Bank in Lansing, Michigan, as a credit analyst. During his time at SVSU, Luke ran cross-country and was a member of the Honors Program. This essay, written for Dr. Meyer’s Sports Economics (ECON 325), analyzes the impact of a new type of running shoe on an athlete’s performance.

Background

On July 17, 2017, Nike debuted the Nike Vaporfly 4%, a marathon running shoe that claimed to revolutionize the sport of running: The Vaporfly will “make runners, on average, four percent more efficient than Nike’s previous fastest marathon shoe” (Nike Inc., 2017). If Nike’s statement is true, the world has not seen an advancement in running shoe technology like this since the invention of spikes in the 1850s, the style of running shoe still used today. Nike’s release of the Vaporfly 4% will cause, and in some respects already has caused, dramatic change to the running community whether at the recreational, collegiate, or professional level. Before the impact of the Vaporfly can be understood, however, the validity of Nike’s assertion that the shoes make runners on average 4% more efficient must be investigated. Through the accumulation of recent peerreviewedresearch,market trendsofdistancerunningshoesinthelastfouryears,andtheassessment of top current marathon and half marathon performances compared with historic records, the truth about Nike’s claim regarding Vaporfly 4% may be uncovered.

Literature Review

With the initial release of the Vaporfly by Nike in 2017, there was naturally skepticism about the marketing of the project. How exactly could a pair of running shoes make someone 4% moreefficient? Theadvertisingsoundedlikeaflashymarketingployrather thanastatement backed by science. This all changed in 2018 when The New York Times came out with an article on the shoe, changing public opinion forever. The New York Times conducted a study “using public race reports and shoe records from Strava, a fitness app […] and found that runners in Vaporflys ran 3 to 4% faster than similar runners wearing other shoes” (Quealy & Katz, 2018). The study used thousands of amateur runners’ Strava data over multiple races to reach this conclusion. From this initial study, the shoe grew in popularity and thus academics began to conduct their own investigations.

In late 2018, Grand Valley State University’s (GVSU’s) Kyle Barnes and Andrew Kilding published a study elevating the Vaporfly’s status to a level no single model of shoe has ever seen. Instead of focusing on recreational runners and measuring based on marathon time improvements like in the Times article, this study used GVSU distance athletes and recorded results based on

“rates of oxygen uptake, carbon dioxide production and biomechanical measures while running” (2018). The research found that the Nike Vaporfly improved running economy by 4.2% compared to an established marathon racing shoe and an improvement of 2.6% on average to track spikes. Because GVSU is debatably the best distance running program in the Great Lakes Intercollegiate Athletic Conference (GLIAC) in the NCAA Division II, these results seemed to confirm that the Vaporfly not only improves the efficiency of recreational runners, but can have a substantial effect on distance athletes at the elite collegiate level. Finally, research by Cornell in 2020 finished the final piece of the puzzle by studying the shoe's effect on professional marathon athletes. Unsurprisingly, the results were similar to the past studies. Of the 307 male distance runners sampled, their race was 1.5–2.9% faster on average, and females ran 0.8–2.4% faster of the 270 sampled (Guiness et al., 2020).

Methods

Because all three studies found significance in the increase of performance of distance running athletes at all levels (i.e., recreational, collegiate, and professional), I used my research to look at how these shoes have affected the highest level of competition in the sport. World Athletics is the governing body for all sporting events involving running (track and field, cross-country, road racing, etc.). World Athletics compiled a list of the 100 fastest times in each event as well as the 100 fastest athletes by results. Lists were based on recorded history of the sport. In the study, I looked at the lists and calculated, based on statistical models, whether the number of fastest times and athletes in the marathon and half marathon were overwhelmingly between the 2018–2022 period, when Nike Vaporflys and their newest models were almost unanimously adopted by the professional distance running community. I then used the sprint and field event lists as constants to observe what a normal 2018–2022 period would have looked like without advancements in technology. To test whether the concentration of recent top 100 fastest times in the marathon and half marathons is significant, I ran a hypothesis test for a two-sample proportion using my test sample and constant. I ran this test for both “all time” lists as well as “best by athletes” list to make sure no single athlete was completely skewing the results. For all time, the value of z is 10.789, and the p-value is less than .00001, meaning the result is significant at p < .01. The same goes for best by athlete category The value of z is 7.0326, and the p-value is less than .00001, making the results significant at p < .01. These findings show that in the last four years, distance athletes have raced top times significantly more than any other sport. These findings are not surprising as every distance event world record from the 5k to the marathon has been broken using the Nike Vaporfly or shoes modeled after it (Muniz-Pardos et al., 2021).

To further demonstrate how skewed recent distance running performances have been compared to previous time periods, I constructed a histogram and Lorenz Curve to better illustrate the phenomenon. Table 1 shows information pulled from World Athletics and is the basis for the running of the two-sample proportion test along with histogram.

Justlookingatthedata,onecall tell thephenomenonisclear:that “All Time”and“BestbyAthlete” performances are abnormally high for the marathon and half marathon. This is again demonstrated in the histogram as both the full and half marathon double that of the next best event (see Figure 1) A Lorenz Curve is used by economists to show how evenly distributed a resource is in a population. In this case, the Lorenz Curve will be used to exhibit how unevenly dispersed the top 100 times are throughout four-year periods (see Figure 2) The top line is a perfectly balanced line over time, meaning out of the 8 time periods constructed, 12.5 out of the 100 best times would have been run in each time period. The more uneven the distribution, the more curved the line will be. Therefore,thehalfandfullmarathon(bottom twolines) aremoreheavily exponential curves, while the 10k, 800, 400 (middle three lines) are far less curved. The distance events’ 100 best times are much less evenly divided amongst periods because the most recent four-year period accounted for around half of the top times.

Competitive Balance of Events over Time

Even without the analysis of different running groups and their performance with the Vaporfly, there is another more obvious indicator that these shoes may do what Nike claims. Since their release in 2017, the technology used in the Vaporfly, most notably the carbon fiber plate and ZoomX foam, has made appearances in six other iterations of Nike shoes. From multiple new generations of the marathon racing shoe, to cross-country flats, to sprinter spikes, Nike has been implementing this design into any performance shoe they can get their hands on. The construction of shoes with this technology does not just stop with Nike; every major shoe company has come out with a marathon racing shoe with a similar design in the last few years. Saucony, New Balance, Adidas, Brooks, ASICS, Hoka, and Sketchers all came out with shoes that rivaled the Vaporfly soon after its release (Running Warehouse, 2021). The expansion of a product line does not necessarily mean the product works the company could just have a great marketing ploy but after five years people would most likely realize the shoes did not show actual results and stop buying them. In itself, this does not give Nike’s 4% claim legitimacy, but on top of the research already laid out, it provides another strong argument in support of Nike’s statement.

Why are runners of all different athletic abilities running faster with the Nike Vaporfly? Theperformancehastodowiththecompositionoftheshoeandhowthat affectsthebody’srunning mechanics. Three main advancements are what make the Vaporfly revolutionary: stack height, ZoomX foam, and a carbon fiber plate. Stack height was found to increase lower-limb length and is believedtoenhancerunning economyas well as“increased springspace within the shoefor more elastic energy to be stored and released during every foot-strike” (Muniz-Pardos et al., 2021, p. 374). Nike’s Invention of the ZoomX foam is another aspect of the shoe that increases responsiveness when impacting the ground. The foam is a polyamide block elastomer called Pebax foam and returnsmoreenergy per stridethan any othermaterial whileat the sametime being lighter and more resilient (Burns & Tam, 2019). Finally, and most importantly, there is the internal carbon fiber plate placed in the shoe. The release of the Nike Vaporfly was the first time the world saw carbonfiber indistanceshoes andisthemainreasonfor theincreasedefficiency. The singlecarbon fiber plate running through the entire sole of the shoe again increases rebound while also providing stiffness to reduce the work rate at the ankle (Burns & Tam, 2019).

What does the introduction of the Nike Vaporfly mean for the competitive nature of distance running and for the competitive balance of all sports? To recognize its impact, the precedent for technological improvements in track and sports in general must be understood. In 1968, both the 200m and 400m world records were broken within 2 weeks (Muniz-Pardos et al., 2021). Both athletes were wearing brush shoes that had 98 small pins, unlike the typical four to six spikes. The governing body of the time banned the new spikes and withdrew the records. In more recent history, similar circumstances occurred in swimming with the LZR Racer swimsuit. A fullbody polyurethane suit cost $200–$500 and would be stretched beyond use every few races (Roberts, 2017). Though costly, the LZR Racer provided extreme aerodynamic advantages. That is why during the Beijing Olympic games, 25 world swimming records were broken, far more than in any other previous event (Roberts, 2017). Soon after, the International Swimming Federation (FINA) banned all full-body polyurethane suits. On the other hand, in long-track speed skating, technological innovation was not banned but embraced. Clap states, with a blade that detachesfrom the back with a hinge in the front and a spring that pulls the blade back into place, were introduced to the long-track speed skating competitions in 1996 with immediate success. Within two years, two seconds were dropped from the men’s 1000m race, something that took 17 years in the past (Mason, 2014). Even with the massive jump in time progression, the clap skate was never banned and is still widely used today.

The examples previously provided raise an important question: what warrants the ban of new sports technology? First, it is important to understand why athletic government bodies ban technology; after all, technology in the world outside of sports is embraced for moving us forward and is only banned if it is harmful or progresses society backward. Sports are unique in their approach to technology because they seek to embody a competitive balance among athletes and sports seek to maintain a sense of gradual progression. Keeping a competitive balance among athletes is the more obvious of the two, as higher performance technology should not only be available to the wealthiest athletes (Qui, 2020). If an individual is talented enough and puts in more training than anyone else, they should theoretically be the best, and no amount of money or sponsorships should change that. A set of gradual progression is important most notably in timebased sports. Over time, humans get faster, whether that involves running, swimming, biking, skating, or anything in between. This occurs for numerous reasons including technology, better training, increased knowledge about the human body, specialization in sports, and a larger population of people, among other reasons. Due to these reasons, there is a gradual progression of records being broken. The problem arises when that progression is sped up too quickly due to “technological doping,”making past records losetheirsignificanceand diminishing theimportance of previous athletes.

With precedent from the past and the outlook of the future considered, World Athletics made a ruling on December 22, 2021, regarding the Vaporfly and the technology that comes with it. Regulation 10.6.1 stated athletic shoes used in competitions “must not contain more than one rigid structure” and regulation 10.6.5 required that soles have “a maximum thickness of 40mm in road events, 25mm in track events from 800m and above” (World Athletics, 2021). These rulings directly address the Vaporfly’s predecessor, the Alphafly, which included a sole thickness over 40mm with multiple carbon fiber plates. Alphaflys were the only shoes affected by the ruling, meaning the use of carbon fiber plates, Pebax foam, and tall stack heights up to 40mm are still allowed in the sport.

It may be hard to believe World Athletics made the right call when looking at past precedent. First, does the technology introduced in the Vaporfly embody competitive imbalance? This does not seem to be the case, as the Vaporfly originally retailed at $250, only $100 more than a normal training shoe, which is a requirement to run. (Now the shoe can go for around $150). A senseofgradualprogressionistheotherconcept considered,andfranklytheprogressionofdistance running seemed to take a massive leap in the years that followed the release of the Vaporfly. In fact, in 2019 Eliud Kipchoge broke the two-hour barrier in the marathon with a 1:59:40 record, when it was believed that through the historic progression of the sport, it would not be until 2075 when that barrier would be breached (Paunescu, 2019). World Athletics could be overlooking the idea of gradual progression, but others believe “competitive sports have reached the edge of human physical limit” (Wang, 2021, p. 4). As athletes maximize the ability of the human body, technological improvements will need to fill the gap to ensure a continued progression of the sport (Qui, 2020).

To better understand the statements made by Zhenyu Qui and Feng Wang, I looked at previous world records over time for four different events. A pattern of inverse growth is demonstrated in the data, meaning Wang is correct in his belief that competitive sports are reaching the edge of human limits, if this small sample of events is representative of the whole population (see Figure 3). In all the events the decrease in world record times starts in large amounts and gets smaller over time. On each graph, there is a solid gray line for the progression of the last 25 years, and it demonstrates how stagnant the events have been recently as all the lines are nearly flat. The only event in recent years with world record times that are outpacing the predicted times by the inverse exponential function is the Marathon, most likely due to its advancement in technology. This is not just a phenomenon in distance running; included is the 1500m freestyle swim, which shows the same trend as the running events. The graphs’ inverse relationships and stagnation in recent years validates Qui’s sentiment that technological improvements are needed to fill the gap if we are to continue progression in sports.

Conclusion

In the pursuit to understand groundbreaking technology as it relates to the sport of distance running, I assessed multiple different outlets to understand the truth. Journal articles at all different competitive levels were presented to explain current research on the Nike Vaporfly. World Athletic Data was then obtained to validate how the Vaporfly time period of 2018–2022 has been abnormal in the number of world-class performances in distance running. Comparsions were done using a two-sample proportion hypothesis test, a histogram, and a Lorenz Curve. Considering how the Vaporfly has affected current market trends of marathon racing shoes was the final way to demonstrate how the shoe has changed distance running forever. The current ramifications of the Vaporfly are apparent due to the evidence provided here, but what this means to the future of distance running is still unclear. By looking at past cases of “technological doping,” the most recent rulings by World Athletics,and Qui and Wang’s statements about the sport, wemay find a glimmer of clarity about what the future may hold.

References

Burns, G T , & Tam, N (2019). Is it the shoes? A simple proposal for regulating footwear in road running. British Journal of Sports Medicine, 54(8), 439–440. https://doi.org/10.1136/ bjsports-2018-100480

Barnes, K. R., & Kilding, A. E. (2018, October 29). A randomized crossover study investigating the running economy of highly-trained male and female distance runners in marathon racing shoes versus track spikes. Sports Medicine, 49(2), 331–342. https://doi.org/10.1007/ s40279018-1012-3

Guinness, J , et al. (2020, October 2). An observational study of the effect of Nike Vaporfly shoes on marathon performance Cornell University, 1–14.

Mason, A (2014, February 15). How a century-old skate design completely changed modern speed skating. Deadspin https://deadspin.com/how-a-century-old-skate-designcompletelychanged -moder-1504286074

Muniz-Pardos, B , et al. (2021). Recent improvements in marathon run times are likely technological, not physiological Sports Medicine, 51(3), 371–378. https://doi.org/10.1007/ s40279-020-01420-7

Nike Inc. (2017, July 17). “Nike Zoom Vaporfly 4%.” Nike News https://news.nike.com/footwear/ nike-zoom-vaporfly-4-release-date https://www.vox.com/recode/2019/11/3/20944257/marathon-nike-shoes-running-sneakers vaporfly-reset-podcast

Paunescu, D. (2019, November 3). Nike’s high-tech Vaporfly sneakers help athletes run 4 percent faster. Should they be banned for providing an unfair advantage? Recode, Vox.

Qiu, Z. (2020). The influence of the design and manufacture of sports equipment on sports. Journal of Physics: Conference Series. 1549(3). https://doi.org/10.1088/1742-6596/1549/3/032039

Quealy, K., and Katz, J. (2018, July 18). Nike says its $250 running shoes will make you run much faster. What if that’s actually true? The New York Times. https://www.nytimes.com/ interactive/2018/07/18/upshot/nike-vaporfly-shoe-strava.html https://www.sciencehistory.org/distillations/winning-skin https://www.runningwarehouse.com/learningcenter/gear_guides/footwear/best-shoeswitha-carbon-plate.html

Roberts, J. (2017, February 19). Winning skin. Distillations, Science History Institute.

RunningWarehouse.(2021,December 30). Thebest carbon-platedrunningshoesof2022. The Best Running Shoes with Carbon Fiber Plates 2022 Gear Guide.

Wang, F. Application of new carbon fiber material in sports equipment. IOP Conference Series: Earth and Environmental Science, 714(3), 2021 https://doi.org/10.1088/17551315/ 714/3/032064

World Athletics. (2021, December 22). Athletic Shoe Regulations. Book C - C2.1A. “World Athletics Home Page.” Worldathletics.org https://www.worldathletics.org/.