This newsletter is called ParentData. Usually I take this to mean “data about parenting.” But an alternative interpretation is “data for parents.” And under that frame, it seems useful to recognize that parents are also people; people with interests and hobbies and goals that range beyond parenting (yes! It’s true!).
Today’s post, then, is inspired by my own interests and hobbies outside of parenting. Or, rather, my one non-work, non-family interest: running. If you follow me on Instagram, you probably get a sense that I like to run. My interest in this activity has ebbed and flowed over the years, but at the moment I would say I take it somewhat seriously (my husband described it recently as a “very intense hobby”). I talked about this evolution a bit on a podcast last week with the great Ali Feller.
As part of this very intense hobby, I recently acquired a pair of “super shoes” — the new-technology racing shoes that supposedly make you faster. When I posted about them, I got questions, and also some skepticism. One commenter told me (nicely) that her husband feels the research does not support the value of these shoes, or that only the Nike versions work. This really felt like a question for data.
So today we’re going to do the data on super shoes. If you’re a runner, hopefully this clears it up. If you’re not … it’s a good time to start, since (spoiler alert) with these shoes you can start faster.
What are super shoes?
The technical name for this shoe type is “carbon-fiber racing shoes.” The key difference between these shoes and others is that the sole contains a carbon-fiber plate and lightweight foams of various types. The shoes are very light and feel springy. The idea is that they improve your running economy — the speed you get for a given effort. Put differently: you put in the effort for an 8-minute mile, and your watch says 7:45 (for example).
The obvious value of the shoes is to make you go faster, but they may also improve recovery times, since you’re putting less effort into a similarly hard workout.
Nike made the first of these shoes, which are still the best known (Vaporfly and Alphafly). More or less every other major shoe brand now makes its own version — Hoka, Brooks, Saucony, etc. The exact configuration of foam and carbon fiber varies across shoes, but the basic idea is similar.
How much do they matter?
One clear indication that these shoes matter is that professional road racing times have come down dramatically during this period. The number of people qualifying for the Olympic Trials in the marathon has almost doubled between 2016 and 2020; the qualifying time hasn’t changed, but the shoes have.
This question is amenable to very detailed data collection. (You know running loves numbers.) One 2018 paper collected controlled data from 18 serious male athletes. They had the athletes run 5-minute intervals in three shoes: a super shoe prototype from Nike and two standard racing shoes. The researchers used various standard breathing and blood tests to measure the “energetic cost” of these efforts. The paper found a 4% lower energetic cost for the super shoes. They translate this to a 3.4% reduction in marathon time. Other trials of the Nike shoe show more like a 2% to 3% lower energy cost on a treadmill, and similar for up- and downhill road running.
This is all effectively lab-based data, but in 2018 the New York Times did some great data journalism using data from the Strava app and public race reports and showed that wearing Vaporflys seemed to improve times by 3% to 4%. This would be quite consistent with the lab data.
(I will say: not everyone agrees with the idea that these shoes matter for running economy. For example, this paper looks at physical biomechanics during running and argues that the shoes do not matter. To me, this seems pretty inconsistent with the reality of what we see with performance.)
Most of the data we have comes from the Nike shoes. This is likely because they were first, and therefore garnered the most interest. However, one 2021 paper compared a wide range of super shoes. This study tested the shoes in 12 male runners, on a treadmill, measuring the outcome on metabolic rate and running mechanics. The authors conclude that the Nike Alphafly, Nike Vaporfly 2, and Asics Metaspeed Sky had similar performance, and all outperformed the other options tested. The Saucony and New Balance models performed better than a traditional shoe but worse than those three; the Hoka and Brooks models did not outperform a traditional shoe.
This analysis is still missing the Adidas shoes, which are popular and were worn by both winners of the 2021 Boston Marathon last year. Overall, though, this gives the sense (to me) that these shoes work in general, although the Nikes are still the category leader in terms of performance.
One thing that’s interesting about this particular paper is that there is a lot of variation across individuals in how responsive they are to the shoes. One athlete of the 12 appears in the data to get a more than 5% performance boost from the Nikes; others have more or less no response.
If you’re a regular runner, what does a 3% improvement in time mean? Let’s say your marathon PR is 4 hours. A 3% improvement is 7 minutes off that PR. In mile time, it’s the difference between 8 minutes and 7:45. Whether that seems like a big change depends on what you’re trying to achieve, but I would venture that most marathoners would be very eager to take 7 minutes off their time at a similar effort.
How do they work?
We do not really know! There are theories, about running form, about the “spring” nature of the carbon fiber, about the foam. It’s not obvious what the most important part of this innovation is. One feature of most of these shoes is they are very tall — the soles are up to 4 centimeters, which is considerably higher than a typical training shoe. Typically a taller sole would add weight, but with the new foam, they are still very light. Being taller is an advantage, so that may be part of it.
But the reality is that it simply isn’t clear exactly why these work and why they work more for some people than others.
Are these even allowed?
Yes, mostly.
It’s been a contentious issue, one that has echoes of the super-suit swimming controversy of the early aughts. Not surprisingly, some people have felt that shoes that give a significant, proven advantage should not be allowed. There are concerns about equity. If not everyone has the same shoe access, this is potentially unfair. There was a bit of a scandal in 2016 when a number of Nike-sponsored runners wore prototype shoes in the Olympic Trials and then in Rio; they won, but the feeling was that perhaps they had an unfair advantage, since other runners could not access the same technology.
As of 2020, the international governing body World Athletics has a new set of rules for elite runners. One is that any shoes must be available for retail purchase for at least four months by the time they’re used in competition. The other is that the shoes cannot contain more than one carbon plate and cannot have a midsole thickness greater than 4 centimeters.
If you are an amateur runner, the second part of this is technically not binding, and there are some available shoes that are higher (the Adidas Adizero Prime X has a 5-centimeter midsole). I would guess most people do not want to race in “illegal” shoes even if it doesn’t necessarily apply to them, but maybe I am wrong!
Bottom line: yes, you can race in these.
Conclusion and my personal anec-data
My broad conclusion is that there is substantial evidence that these new shoes make people run faster. If you are an elite professional runner (I’m sure many of you are reading my newsletter!), you should have these.
For a regular amateur runner, the question is whether the extra speed is worth the quite hefty price tag for a set of shoes you will mostly wear for races and harder workouts. If you’re not racing, or running for time, the argument is perhaps less compelling. If you’re racing, these will probably make you faster. The counterargument, other than cost, comes from the running purists who do not want a faster time “just because of the shoes.”
I will end with my own anec-data. I got a pair of the Adidas Adizero Adios Pro 3 (I tried the Nikes, but my very wide foot did not fit in them). I found them very, very effective. Almost like magic. The first time I took them out, I ran at what I know to be an 8-minute-effort pace, and my mile time beeped at 7:30. It was creepy but sort of awesome.
So I raced a 10K in them, and for me it made a big difference (I ran 42:02!). It felt a little like getting away with something, but in the end, the last mile of a race feels like you are going to die no matter what the shoes. I’m still waiting for them to innovate that feeling away.
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