Only Some Runners Ran Faster Using Carbon Plated Shoes

Alphafly (L) and Vaporfly from weartesters.com

Ever since Kipchoge ran a sub-2 hour marathon in the carbon plated Nike Alphafly in 2019, every single of my patients who participate in running races want to race in a pair too. Back then, those super shoes were really hard to get a hold of, for almost a year. If you did get your hands on a pair, they cost a bomb too.

Now that these super shoes are more easily available (since many other brands other than Nike also make carbon plated shoes), is it worth splurging on them? Especially if you're trying to clock a personal best timing in your next race.

How does the original Nike super shoe (the Vaporfly) work? There are 2 novel components to this question. First, the super thick cushioned midsole Nike calls ZoomX. This new foam is super light, 31 millimeters high at the heel, which is 50 percent thicker than comparable shoes without being heavier. You can squish it and it springs back to shape quickly. This means it returns all the energy you applied to squish it. 

Next is the curved carbon fiber plate inside the midsole (pictured above). It is thought that the carbon fiber plate(s) acts like a spring, bending as your foot lands and then catapulting you forward as it springs back into position. This helps running economy (reduces energy expenditure) so you can run faster.

Ever since Nike launched their Vaporfly in 2017, which has since been updated a few times, there have been calls and debates to have the shoe disallowed in competition. Opposers have labelled the shoe as technical 'doping'. When subsequent studies showed that these Nike shoes gave up to a 4 percent advantage (Barnes and Kilding, 2019), other runners were obviously upset. 

Especially after two Nike sponsored runners in the United States used the prototype version at the 2016 Olympic trials (women's 1st and 3rd places) and qualified for the Olympics.

Shalaya Kipp felt that the prototype Vaporfly's kept her training partner, Kara Goucher (4th place), off the Olympic team after signing up with Skechers. She left Nike in 2014 beacause of the infamous Alberto Salazar "Oregon project". Had Goucher stayed with Nike, she may have qualified for her third Olympics in 2016. At the actual 2016 Olympics, the top 3 male finishers all wore the same Nike prototype shoe.

In fact Nike scored a major coup when they offered all other runners who qualified in the 2020 USA marathon Olympic trials a pair of the Alphafly's to level the playing field.

Before you buy a pair of carbon plated shoes, consider the following study. It was published just last month looking at 96 runners using 2 different prototypes of carbon plated  shoes. The shoes differed only by the forefoot bending stiffness. The runners were first assessed for their VO2 max and maximum aerobic speed. Running economy and stride kinematics were also recorded during the trials. 

The researchers did not find any significant difference in running economy between the 2 different shoe stiffness for the group as a whole. Some runners' running economy improved when the carbon fiber plate was stiffer while in other runners, their running economy deteriorated. To be more specific, the faster runners took advantage of the increased stiffness (carbon fiber plates) while the slower runners did not.

The authors emphasized the importance of individual response to using carbon fiber plates to enhance running performance is runner specific. 

For now, the carbon plates remain street legal for us mortal runners in competition. If you do get them, remember to break them in with a few runs instead of just saving them for race day. The midsole thickness definitely makes your foot more unstable especially when going around sharp corners or while making a u-turn in an out and back route.

References

BarnesKR and Kilding AE(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. 49(2): 331-342. DOI: 10.1007/s40279-018-1012-3.

Beck ON, Golyski PR and Sawiki GS (2020). Adder Carbon Fiber To Shoe Soles May Not Improve Running Economy: A Muscle-level Explanation. Sci Rep. 10: 17154. DOI: 10.1038/s41598-020-74097-7

Chollet M, Michlet S, Horvais N et al (2022). Individual Physiological Responses To Changes In Shoe Bending Stiffness: A Cluster Analysis Study On 96 Runners. Eur J Appl Physiol. DOI: 10.1007/s00421-022-05060-9