Why Nike’s VaporFly 4% should have been called the VaporFly Unleaded, and how dodgy science ruined running shoes.
There is a joke that does the rounds every time there is a cycle of fuel price hikes, along the lines of “with the new fuel price it’s cheaper to just take meth and run everywhere.” I wouldn’t be surprised if there were early versions of this joke about horse shoes and snuff, but it may now be time to retire it for good — running is no longer the cheap, accessible sport that it once was. The advent of the so-called ‘super-shoe’ means that running, at least competitively, now costs more, per kilometer, than just about any other means of getting around.
The super-shoes are best exemplified by Nike’s flagships, the AlphaFly and VaporFly lines. These shoes are now into their second and third iterations, respectively, having dominated podiums at the world’s major marathons, and played a predominant part in the recent rewriting of the road-running record books. Perhaps most famously, Eliud Kipchoge used versions of the AlphaFly for his official world marathon record as well as his sub 2-hour exhibition run. Kipchoge’s slim 52kg frame plays up the ridiculousness of the bulky super shoes, particularly in contrast to the sleek low-profile racing flats that predominated elite racing until recently.
A recent study showed that when tested by elite athletes, Nike’s super shoes provided a 4% improvement in running efficiency, a figure that has featured prominently not just in conversation in running circles but even directly in Nike’s advertising — an early version of the VaporFly shoe was actually named the VaporFly 4%. However, it must be noted that Nike sponsored that study themselves, always a red flag for research objectivity. When human subjects are involved, numerous sources of bias can creep in and, of course, the double-blinding that is the norm in all medical research is impossible when the different shoes are visibly obvious to researchers and subjects alike. Can the placebo effect affect running economy? Quite possibly. Is it possible for bias to have exerted subtle influence in choosing when to run the experimental efforts and when to run in the control shoes? Also possible.
More importantly, could putting lead weights in shoes decrease their running economy? Obviously yes. As ridiculous as it may sound, the researchers did indeed place lead pellets in the control shoes.
Ostensibly, this was to equalize the weights of the shoes to “remove the confounding effects of shoe weight.” This logic is intrinsically spurious, analogous to saying that busses are faster than cars, if the cars weigh the same as the busses. The fact that large quantities of foam in ‘super shoes’ add weight does detract from their efficiency; it is a property of the shoes, not an external confounder and it should be included, not controlled for.
The researchers did not state where the lead pellets were placed, or how, and their effects on the mechanical properties of the shoes may exceed just the weight increase. In short, the methodology of this study was clearly and intentionally manipulated to favour Nike’s new shoe technology, and the 4% figure can be safely discarded as intentionally misleading.
Subsequent research has in fact shown some improvements in running economy from super-shoes, including Nike’s flagships as well as other brands. However, the inability to double-blind the research remains an issue and the newer findings are considerably more modest than the 4% figure. A 1% improvement in running performance may be the more realistic estimate, based on research which is admittedly a bit too thin to be conclusive.
Super shoes come with other drawbacks, however. Their extremely large stack heights make them unwieldy for cornering, impair their stability on uneven surfaces, and just generally make them unsuitable for activities other than running in a straight line on a hard surface. This doesn’t just cast some doubt on how test results on treadmills translate to real roads, it also means that runners can’t repurpose their racing shoes for other activities at the end of their racing lifespan. Super shoes have also been found to have comparatively short racing lifespans, with some reviewers saying that some models are only good for a couple hundred miles before they lose their bounce.
They are also spectacularly expensive. The Nike Alphafly retails at an eye-watering $275 and, while reviewers differ on their lifespan, only a scant few report them lasting 300 miles. Optimistically, then, running in these shoes costs, optimistically, a dollar a mile — on the same order as taking an Uber.
One might argue that the solution is simple — leave the super shoes on the shelf and just keep buying the same racing flats we used to. That doesn’t work, for two reasons.
The first is that competitive runners will be hard-pressed to pass up even a 1% advantage if it’s on offer. Everyone getting 1% faster doesn’t actually benefit anyone, but if everyone else gets 1% faster, and you don’t, disgruntlement is inevitable. As sportspeople, we are also unfortunately quite susceptible to hype and are in a never-ending quest for the newest and best equipment.
Perhaps trickier to solve is the fact that all the major shoe companies have stopped making low-profile racing flats entirely. Super shoes, with their hefty price tags, are doubtless more lucrative in their own right but from the standpoint of shoe manufacturers and retailers, short lifespan and narrow use profile are features, not bugs. The shoes at lower price points don’t feature the carbon plates of super shoes, but do have the same enormous foam stacks, thus carrying all the other disadvantages and still necessitating more pairs of shoes to cover the same set of uses.
For runners this means that our shoes will be heavier and our wallets lighter. It also means that in years to come, there may be fewer of us toeing the start-line at races.
