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The impact of super shoes has been profound. Since Nike’s Vaporfly 4% hit the roads in 2016, the controversial trainers – with their combination of a carbon plate, big stack of high-rebound midsole foam and lightweight uppers – have changed running at every level. Toppling records and forcing regulation changes.
Kenyan Eliud Kichoge took the men’s marathon world record in Berlin in 2018, followed by that historic sub-2-hour marathon in 2019. Both in the AlphaFly. Brigid Kosgei beat Paula Radcliffe’s women’s world marathon record in the same shoe. Japan’s Mariko Yugeta became the first woman aged 60 or over to break the three hour marathon barrier when she ran 2:59:15 wearing the Vaporfly.
Nike hasn’t had all the glory though. Twenty-year-old Kenyan Rhonex Kipruto claimed the men’s 10km road world record in 2020 wearing a pair of prototype Adidas carbon shoes. Ethiopia’s Derara Hurisa was disqualified after winning the Vienna Marathon wearing the Adidas Adizero Prime X, which has soles that are five centimetres (50 mm) – thicker than the new regulation 40mm stack height.
In ultra running, Jim Walmsley set the 50-mile world record in HOKA’s Carbon X while Lithuanian Runner Sania Sorokin captured the 100-mile track world record running an average 6:45 min/mile pace in a combination of Hoka Carbon X2 and the Nike AlphaFly.
Fast forward to 2021 and the revolution is still gathering pace. Every running shoe brand from Adidas, Brooks and Saucony to Hoka – and even The North Face – now has its own carbon racer. But have Nike’s rivals levelled the playing field as much as the marketers would have us believe? Not according to the scientists.
New research from Austin State University has revealed that despite hefty price tags and bold claims, some carbon running shoes offer little or no benefits compared to a traditional non-carbon race shoe. The study’s findings also suggest that Nike still leads the pack when it comes to performance-enhancing running economy, and its authors advise runners to think carefully before buying into the marketing promises.
While previous carbon shoe studies validated the performance enhancements of Nike’s Vaporfly and AlphaFly shoes, this is the first study to compare the leading carbon shoes against each other and a traditional race shoe, to find out which delivers the biggest gains.
The study looked at how the high-end shoes performed on 12 trained, male distance runners, size 10-11 US, who’d been running at least three times a week for the previous three months. Each runner had also clocked a sub-17:30 minute, 5km race performance, (or equivalent race performance for distances 3km to marathon) within the last year and had the ability to run below the lactate threshold at the 16km/hr tested running economy speed. That’s just over 6 minutes/mile or 3.75 minutes/km, so the faster end of amateur runners.
Researchers selected seven carbon shoes based on availability at the time, with Adidas a notable omission. These comprised: Nike AlphaFly, Nike Vaporfly 2, Saucony Endorphin Pro, Hoka Rocket X, Asics Metaspeed Sky, New Balance RC Elite and the Brooks Hyperion Elite 2. The eighth non-carbon comparison shoe was the Asics Hyperspeed.
The shoes were tested during two sessions, in a random sequence over 8x5-minute trials, running on a treadmill at 16km/hr with a 5-minute rest between. On the second visit, the shoes were tested in reverse/mirrored order.
Each runner’s metabolic and running mechanics data were collected and averaged across the visits. Any changes in running economy, aka the ability to run at faster speeds while working at the same physiological intensity, were logged.
“I’d used the Hoka Carbon X for marathon training and was about to buy the second-generation,” says Dustin Joubert, the study’s lead author. “But before spending $200, I decided to do a little case study on myself and found there was no benefit when compared to my regular racing flats. I did the same with the Alphafly and discovered I was a 4% responder. That’s when I realised the playing field is clearly not equal.”
“If you look at the elite landscape as well, everybody's running in Nike or Adidas, and then you get a sprinkling of Asics Metaspeed in there,” says Joubert. “You can't always blindly trust the anecdote, but, as sports scientists, we should probably follow the anecdote sometimes. If all the elites have figured this out, or are sceptical enough, then maybe there’s a message for consumers too.”
The study results suggest that the elite runners' instincts were spot on and Joubert was right to follow the anecdote.
Despite the influx of new carbon contenders, Joubert and his research partner Garrett Jones discovered that Nike’s carbon racers still give runners a crucial performance edge. Only Asics closed the gap with its Metaspeed Sky. But perhaps more surprisingly, they also found that some carbon shoes offer little or no significant benefits over a traditional race shoe. Therefore some of us might be better off saving our money.
The Hoka Rocket X and Brooks Hyperion Elite 2 failed to significantly improve running economy compared to the traditional Asics Hyperspeed shoe. And while the Saucony Endorphin Pro, Asics Metaspeed Sky, Nike Vaporfly 2 and Nike Alphafly all significantly improved economy over the regular shoe, the New Balance RC Elite and Saucony Endorphin Pro did so by less than 1.5 per cent on average. They also performed significantly worse than the Asics Metaspeed Sky and the two Nike shoes, which all generated greater than 2.5 per cent improvements.
“I think we can say across the broad landscape, things haven't levelled up,” says Joubert, and while the carbon plate has grabbed the headlines, he believes the crucial difference – where Nike’s rivals are falling short – could well be the foam.
“It is evident from our data that simply including a carbon plate or increasing the stack height in a racing shoe does not confer equal improvements in economy,” the report states. “This would suggest that the foam and/or interaction of the foam and the plate is crucial to the economy benefits.”
“We didn't do any testing of the foam. But if we look at this line-up and what's different about these shoes, they all have carbon plates, they've all increased stack. But they have different foam,” says Joubert.
“It's almost like Nike misdirected everyone by putting the plate in the shoe. Everyone's chasing the low hanging fruit – it's easy to add a carbon plate – but the real difference is in the performance of the foam.”
Previous research paints a similar picture. One study cut the carbon plate in the Nike Vaporfly to reduce the longitudinal bending stiffness but found no changes in running economy compared to an intact version. That suggests that the PEBA-based ZoomX foam in the Nike Vaporfly is the critical factor.
“Even when shoes are known to utilize similar foam materials, such as the case with the PEBA-based Saucony Endorphin Pro and Nike Vaporfly and Alphafly, we see differences in economy in the current study,” says Joubert.
It’s almost certainly why the secret sauce of those foams isn’t something the brands tend to share. Not knowing exactly what you’re buying in next-generation shoes can make it hard for consumers to judge which offer genuine benefits.
Some of the shoes tested in the study have since been superseded by second-generation models, the Saucony Endorphin Pro 2 and the New Balance RC Elite 2, for example. So have these shoes changed enough to suggest the gap is closing? Not necessarily.
“Saucony didn’t do a whole lot to update the Endorphin Pro with the second version. You get the same stack of PEBA-based midsole foam with minor tweaks to the uppers and we didn’t notice any change in the performance of the shoe in our testing,” says Nick Harris-Fry, shoe tester for The Run Testers who has run in most of the carbon shoes currently on sale.
“There is now the Endorphin Pro+, which is lighter than the standard Pro 2, but again the changes were mainly in the upper so the performance from the plate and foam is likely to be unchanged.”
New Balance’s changes to the RC Elite V2 might be more significant. “This has a significantly higher stack than the original RC Elite and feels more like a super shoe in the mould of the Alphafly or Vaporfly,” says Harris-Fry.
“New Balance tweaks its foam between shoes, but it’s not easy to ascertain if the Fuelcell foam in this model is markedly different. The higher stack allows for more of a curve to the carbon plate, which we found improved the performance of the shoe and could affect how it would have scored in this study.”
Beyond running economy, the Austin State University study also threw up some interesting insights into how the higher-responding carbon shoes appeared to make runners move a certain way, in order to unlock the biggest benefits of shoes like the Alphafly. Or at least a certain running technique worked best with the top-performing shoes.
“If you look at the trends for the higher responsive shoes, people are running in them with slower cadences, more vertical oscillation, and longer stride lengths,” says Joubert.
“So it's like people are using that extra energy return to lengthen their stride a little bit. Whereas normally, we think of things like a faster cadence, less wasted vertical oscillation, and a little bit shorter stride as the normal correlates that we would associate with good economy.”
It’s a pattern that movement expert and author of The Lost Art of Running, Shane Benzie, recognises. Benzie has studied thousands of runners all over the world – including world beaters – in a bid to understand what makes our legs tick.
“When you look at good runners stats, the best runners always spend little time on the ground, a lot of time in the air,” says Benzie. But he suggests that carbon shoes alone aren't necessarily the answer to improved efficiency. Adopting the right running form to maximise the effects of a carbon shoe is what really counts.
“You have to run well and you have to interact correctly with the ground for that carbon to help you. If you're trying to move over the ground and not really interact with it, trying not to hit it, trying not to create any air, the carbon springs aren't going to help you very much.”
“I believe that the best way to land when we run is to land on the foot’s natural dome with a full foot and not, for example, striking the ground first with our heel or only landing on our forefoot.” This is what Benzie calls a tripod landing, engaging the foot’s natural arches to create a dome that dissipates impact and creates propulsion.
“If you land on a nice tripod with great stability, and then you push off, you’re effectively engaging your plantar fascia [the thick elastic connective tissue that supports the foot arch] to do the work for you, but also the carbon spring is now helping as well. What it's potentially doing is inspiring runners to use their natural assets, rather than just relying on that spring in the trainer.”
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This article was originally published by WIRED UK
