ADVERTISEMENT
Running Super Shoes: Truly Super, or Just Hype?
The running shoe has evolved remarkably over the past 150-plus years. In 1865, the Dutton and Thorowgood Shoe Company in England made the first known specialized running shoe, with a laced leather upper, thin leather sole, and embedded steel spikes for better running traction. In 1920, a shoemaker from Germany, Adolph “Adi” Dassler, improved on racing shoe design with his lightweight, very thin leather upper, thin leather sole racing shoe with six steel spikes embedded within the forefoot. Dassler provided this revolutionary footwear to American sprinter Jesse Owens, for his competitions at the 1936 Berlin Olympics, in which Owens won gold medals in the 100- and 200-meter sprints, long jump, and 4 × 100-meter relay.1 Thirteen years later, in 1949, Dassler began his shoe company, Adidas, which is now the largest sportswear manufacturer in Europe.2
Since then, progression in running shoe technology and design continues, with shoe manufacturers striving to produce lighter, faster, more cushioned, and more comfortable running shoes. Notable improvements in running shoe uppers using synthetic fabrics such as nylon make running shoes more light, flexible, and comfortable than their older leather-upper counterparts from a half-century ago. In addition, the transition from leather soles to thin rubber shoes and now to running shoe soles with relatively lightweight, thick, cushioned copolymer foams such as ethylene vinyl acetate (EVA) have helped pave the way for the modern running shoe; one that is not only light on the foot, but also more cushioned and more comfortable for the running athlete.3
Shoe Design and Running Performance: A Historical Perspective
With these improvements in running shoe design, modern materials, and advanced manufacturing techniques, also came gradual improvements in distance racing performances. For example, American Johnny Hayes held the 1908 world record time in the men’s marathon of 2:55:18.4 Over the next century, gradual, relatively incremental improvements in marathon record times occurred, culminating in 2014 when Dennis Kimetto of Kenya improved on the world record marathon time with a time of 2:02:57, which is 52 minutes, or 2 minutes per mile, faster than Hayes ran 106 years earlier.4 While the reasons for such improvements are obviously multifactorial, including better exercise research, improved nutrition, and better training methods, improvements in running shoe design and technology have certainly also contributed.
Over the half-century since the “running boom” of the 1970s,5 the distance running community expected these small gradual improvements in marathon racing times, whether due to better research, better training methods, better nutrition or other factors. However, this gradual, incremental pattern all changed when the running shoe company Nike introduced their carbon-plated, thick-midsoled, lightweight running shoe, the Nike Vaporfly (VF), to the international distance racing community. The top three finishers in the marathon at the 2016 Rio Olympics wore the Nike VF racing shoe. Two years later, Kenyan Eliud Kipchoge also wore a version of the same shoe when he set the official world record of 2:01:39 at the 2018 Berlin Marathon. Kipchoge’s 78-second improvement on the existing world record was the largest improvement in over 50 years. In addition, Kenyan Brigid Kosgei beat Paula Radcliffe’s 2005 world marathon record in the latest version of the Nike VF shoes, reducing the mark by 81 seconds.6
In 2018, The New York Times studied the race data from 500,000 marathon and half marathon running times since 2014. Using public race reports and shoe records from a popular fitness app, they found that runners wearing Nike VF shoes ran 3 to 4 percent faster than similar runners wearing other shoes and more than 1 percent faster than the next-fastest racing shoe.7 Likewise, in a 2020 marathon performance study of elite and sub-elite athletes from 2015 to 2019, the estimated effect on marathon times of wearing the Nike VF shoes was substantial. This study estimated that Nike VF shoes improved men’s marathon times between 2.0 and 3.9 minutes, while improving women’s marathon times between 0.8 and 3.5 minutes. The authors further estimated that the men’s marathon times improved by 1.4 to 2.8 percent and women’s marathon times improved by 0.6 to 2.2 percent while wearing the Nike VF shoes.8
The Emergence of the “Super Shoe:” What The Research Reveals
Since the Nike VF, and its subsequent variations, the Nike Alphafly and Nike Next%, runners wearing these shoes broke an increasing number of international distance running records.6 Now, with other shoe manufacturers using similar design materials and technology as the Nike VF, the term “super shoe” sometimes describes those running shoes with a thicker, lightweight foam midsole and a carbon-fiber plate embedded within the midsole. The design of these super shoes aim specifically to improve distance running performances over more traditional racing flats. Some of the more popular running super shoes currently marketed to runners include the Nike VF Next%, Saucony Endorphin Pro, New Balance FuelCell RC Elite, Brooks Hyperion Elite, Adidas Adizero Adios Pro and the Nike Alphafly Next%.9
With the improvements in distance running race performances seen in runners wearing such super shoes, does the scientific evidence support the claims that these super shoes have the potential to improve the race performances for many distance runners? In other words, are these newer running shoes truly “super,” or are the claims of improved distance race times simply marketing hype?
The first scientific paper published on the potential performance benefits of the Nike VF running shoe looked at 18 sub-elite runners, all of who had recently run a 31-minute 10,000-meter time at sea level. The subjects ran six, 5-minute trials in two popular marathon racing flats, the Nike Zoom Streak 6 (NS) and the Adidas Adizero Adios Boost 2 (AB), and in the new prototype shoe (at that time), the Nike VF. Since the NS and Nike VF shoes were lighter in weight than the AB shoe, researchers added lead pellets to the NS and the Nike VF shoe to equalize the mass of all three running shoes.10
Material testing showed that the sole of the Nike VF was more compliant (ie less stiff) than the soles of either the NS or AB shoes. The Nike VF shoes deformed 11.9 mm, while the NS shoe deformed only 6.1 mm, and the AB shoe sole deformed only 5.9 mm. In other words, for a given compression loading force on the shoe sole, the Nike VF shoe midsole deformed during impact testing nearly double the amount of the two other running shoes. In addition, the Nike VF sole was more resilient than the other two shoes, with an 87 percent energy return in the Nike VF, versus only 75.5 percent in the AB shoe and 65.5 percebt in the NS shoe. In other words, the Nike VF shoe sole returned twice the amount of mechanical energy as the soles of the other two racing shoes, with most of that energy return coming from the increased compliance and only somewhat from the greater resilience.10
Next, they measured the metabolic energy expended by the 18 runners in each of the three running shoes at three running velocities, 14 km/h (6:54 mile pace), 16 km/h (6:02 mile pace) and 18 km/h (5:22 mile pace) on an instrumented treadmill. The Nike VF shoe substantially lowered the energetic cost of running, by 4 percent on average, and at all three running velocities compared to the other two running shoes. Since the Nike VF shoes allowed the runners to expend 4 percent less metabolic energy than the other two marathon racing shoes tested, they called this first generation of the VF super shoe the Nike Vaporfly 4%.10
One of the other interesting findings from the research by Hoogkamer and team was that runners took longer and less frequent running steps in the VF shoe than the AB and NS shoes, indicating that the VF running shoe likely allowed the runners to bounce higher with each running step.10 This higher bounce with each running step in the VF running shoe was also confirmed by research done by Hunter and coworkers. These authors measured the same three shoes, and found that the VF shoe caused the center of mass of the runner to bounce 15 mm higher (ie 15 mm more vertical rise and fall of the center of mass) than with the AB and NS shoes with each running step.11
Super Shoe Features: What is the Impact?
To better understand the science behind these apparent performance benefits, it is important to discuss how the Nike VF shoes are structurally different from other shoes commonly used in elite distance running competitions before they made their debut at the 2016 Rio Olympics. First of all, the Nike VF shoe has a remarkably thick and lightweight (ie less dense) sole compared to other racing flats. The Nike VF 4% has a heel stack height (ie rearfoot sole thickness) of 39 mm and the Nike VF Next% has a heel stack height of 40 mm. Equally as thick in the shoe sole is the Nike Alphafly shoe, a subsequent variant of the Nike VF. Eliud Kipchoge wore the Nike Alphafly when, while being paced by 41 other runners, he broke the 2-hour barrier in a marathon event in Vienna, Austria in October 2019.12
Even though the sole of the Nike VF looks huge, having an enormous amount of midsole volume, they are actually no heavier than more traditional racing flats. Part of the reason is that the Nike VF sole unit is made of a relatively new midsole foam known as PEBA (polyether block amide). Compared to conventional EVA materials which return only about 65 percent of the energy to the runner during each running step, PEBA foam returns about 85 percent.10 So, the thick layer of a newer low-density and lightweight foam in its sole and the PEBA foam in the midsoles exhibits significant energy-return capability.
Having a running shoe that is light in weight (ie low mass), has a very significant effect on the metabolic energy expended during running. The consensus from previous scientific research regarding the metabolic energy required to run in shoes of different mass is that for every 100 grams of added weight to the runner’s foot, the metabolic energy needed increases by about 1 percent.13-15
The final unique structural feature is the full-length carbon-fiber plate embedded within the PEBA foam midsole. The exact performance enhancing mechanism of this plate within the Nike VF shoe is still unknown. But, researchers believe that it increases the longitudinal bending stiffness of the shoe sole so that the foot effectively becomes a stiffer and longer lever during propulsion.16 Since the carbon-fiber plate prevents dorsiflexion of the MTPJs during propulsion, it is also possible that this eliminates the “negative work” of the foot during propulsion when the toes normally dorsiflex, helping to push the foot forward.16
One common belief about the carbon-fiber plates within these super shoes, unfortunately that I’ve noticed has been repeated continuously by many on the internet and by running shoe “experts,” is that these “sole-stiffening” plates act as a “spring,” somehow propelling the runner forward with each step. This notion that the carbon-fiber plate somehow acts as a spring is highly unlikely since research shows that the carbon-fiber plate embedded within the super shoe midsole actually causes an increase the longitudinal bending stiffness of the shoe sole, and doesn’t function as a spring.19 Increasing the longitudinal bending stiffness in these super shoes, many of which are made with highly compliant midsole foams such as PEBA, helps prevent excessive deformation of the running shoe midsole during running propulsion. In other words, the carbon-fiber plate, by increasing the longitudinal bending stiffness of the super shoe midsole, does increase the lever arm for running propulsion, which, in turn, likely provides for more power for the foot to push-off the ground during running.17-19
Another feature of many running super shoes is their rocker-sole construction, largely implemented by adding that curved carbon-fiber plate to the midsole. A rocker-sole type of shoe construction may be necessary not only because of the stiff carbon-fiber plate, but also the extremely thick forefoot midsole, both of which increase the bending stiffness within the forefoot region. The rocker sole may help facilitate being able moving one’s center of mass more easily over the forefoot into propulsion than if the rocker-sole was not present. Biomechanics researcher Benno Nigg opines that these rocker-soled running shoe designs improve running economy by what he calls the “teeter-totter effect.”20 He is one of the few to believe that the carbon-fiber plate is a major contributor to performance improvements in the running super shoes, and not so much the extra-thick, highly compliant, resilient and lightweight midsole foams.20
Concluding Thoughts
Overall, both scientific research and race data over the past six years seem to agree on that the Nike VF shoe, and other running super shoes, can substantially improve the metabolic economy of running and improve race times for recreational, sub-elite and elite distance runners. These improvements are likely due to four distinct factors:
The PEBA foam midsole is not only ultra-light for a given volume of midsole material (ie less dense), but is also superior in compliance and energy-returning abilities to all other previously existing running shoe midsole materials.
The Nike VF midsole foam is thicker than practically any other running shoe.
The full-length carbon-fiber plate within the PEBA midsole reduces negative work at the MTPJs during propulsion and increases the lever arm of the foot for the ankle plantarflexors to push off during propulsion. However, the carbon-fiber plate within the midsole does not likely function as a spring, as many have suggested.
The rocker-shape of the shoe sole allows improved and more efficient weight transfer of the center of mass of the body during the late support phase of running and is a necessary shoe design parameter due to the thick forefoot midsole and carbon-fiber plate, both of which significantly stiffen the forefoot region.
Of course, further research is necessary to better understand why super shoes sometimes work better at improving race times more for some runners than others. But, as far as distance running records and running shoe technology are concerned, the Nike VF shoe truly has lived up to its hype over the past six years, radically changing the running shoe industry and the performance-enhancing abilities of distance racing shoes.
Dr. Kirby is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is in private practice in Sacramento, Calif.
References
1. Cavanagh PR. The Running Shoe Book. Anderson World;1980:18-33.
2. History. Adidas website. Available at: https://www.adidas-group.com/en/about/history/ . Accessed April 4, 2022.
3. Cavanagh PR. The Running Shoe Book. Anderson World; 1980:34-51.
4. Marathon world record progression. Available at: https://en.wikipedia.org/wiki/Marathon_world_record_progression . Accessed April 4, 2022.
5. Nilson F, Lundkvist E, Wagnsson S, Gustafson H. Has the second ‘running boom’ democratized running? A study on the sociodemographic characteristics of finishers at the world’s largest half marathon. Sport in Society. 2019;24(4):659-669.
6. Nike’s Vaporfly running shoes and tumbling records. Reuters. Available at: https://www.reuters.com/article/uk-athletics-shoe-factbox/nikes-vaporfly-running-shoes-and-tumbling-records-idUKKBN1ZN0MT. Accessed April 4, 2022.
7. Quealy K, Katz J. Nike says its $250 running shoes will make you run much faster. What if that’s actually true. The New York Times. Available at: https://www.nytimes.com/interactive/2018/07/18/upshot/nike-vaporfly-shoe-strava.html . Published July 18, 2018. Accessed April 18, 2022.
8. Guinness J, Bhattacharya D, Chen J, Chen M, Loh A. An observational study of the effect of Nike Vaporfly shoes on marathon performance. arXiv:2002.06105 . Accessed April 4, 2020.
9. McGuire J. The best carbon fiber running shoes 2022. Tom’s Guide. Available at: https://www.tomsguide.com/best-picks/best-carbon-fiber-running-shoes . Updated March 30, 2022. Accessed April 4, 2022.
10. Hoogkamer W, Kipp S, Frank J, Farina E, Luo G, Kram R. A comparison of the energetic cost of running in marathon racing shoes. Sports Med. 2018;48:1009-1019.
11. Hunter I, McLeod A, Valentine D, Low T, Ward J, Hager R. Running economy, mechanics, and marathon racing shoes. J Sports Sci. 2019;37:2367-2373.
12. Ineos 1:59 challenge. Available at: https://en.wikipedia.org/wiki/Ineos_1:59_Challenge . Accessed April 4, 2022.
13. Catlin ME, Dressendorfer RH. Effect of shoe weight on the energy cost of running. Med Sci Sports. 1979;11:80.
14. Frederick EC, Daniels JT, Hayes JW. The effect of shoe weight on the aerobic demands of running. In: Bachl N, Prokop L, Suckert R (eds). Current Topics in Sports Medicine. Urban & Schwarzenberg;1984:616-625.
15. Frederick EC. The energy cost of load carriage on the feet during running. In: Winter DA, Norman RW, et al, eds. Biomechanics IX-B. Human Kinetics Publishers;1985:295-300.
16. Willwacher S, König M, Potthast W, Brüggemann GP. Does specific footwear facilitate energy storage and return at the metatarsophalangeal joint in running? J Appl Biomech. 2013;29(5):583-592.
17. Roy JP, Stefanyshyn DJ. Shoe midsole longitudinal bending stiffness and running economy, joint energy, and EMG. Med Sci Sports Exerc. 2006;38(3):562-569.
18. Willwacher S, König M, Braunstein B, Goldmann JP, Brüggemann GP. The gearing function of running shoe longitudinal bending stiffness. Gait Posture. 2014;40(3):386-390.
19. Ortega JA, Healey LA, Swinnen W, Hoogkamer W. Energetics and biomechanics of running footwear with increased longitudinal bending stiffness: a narrative review. Sports Med. 2021;51(5):873-894.
20. Nigg BM, Cigoja S, Nigg SR. Teeter-totter effect: A new mechanism to understand shoe-related improvements in long-distance running. Br J Sports Med. 2021;55(9):462-463.
