The most interesting studies, in many cases, are the ones whose initial hypotheses get torpedoed by the data.
As part of a massive biomechanics project during the 2017 world track and field championships in London, researchers rigged up high-speed cameras on the marathon course to assess the foot-strike patterns of the passing runners at four points during the race. Their hypotheses were that most of these smooth-striding whippets would land on their midfoot or forefoot, but that the proportion of heel-strikers would significantly increase as the race progressed. They were wrong on both counts.
A team of researchers led by Brian Hanley of Leeds Beckett University in Britain just published the results of their analysis in the Journal of Biomechanics. (Some of the data was initially released by the IAAF last year, as I noted here, but the new paper presents a more detailed analysis.) The paper’s title is “Most marathon runners at the 2017 IAAF World Championships were rearfoot strikers, and most did not change footstrike pattern”—a concise summary of the findings, but one that’s sure to stir up a debate that’s been simmering for the past decade.
In fact, people have been arguing about how your foot should hit the ground for well over a century, but the modern version of the debate kicked off with the publication of Born to Run in 2009. The basic argument is that landing on your midfoot or forefoot harnesses the natural shock-absorbing properties of soft tissues like your Achilles tendon, thus reducing the force with which you crash into the ground compared to landing on your heel. In the process, your Achilles also stretches like an elastic band to store energy which it then feeds back into your next stride. It’s a win-win proposition for injury prevention and efficiency—in theory, at least.
There are various possible counterarguments to this view, including evidence that outsourcing the job of cushioning your landing from your tendons to the midsole of your shoes is actually easier and consequently saves energy. And there are counter-counterarguments, and so on, ad infinitum. At a certain point, it’s reasonable to simply ask what the best runners in the world do, with the assumption that those who are doing something seriously wrong will probably be beaten by those who are doing it right.
This approach has lots of confounders, of course. Many of the world’s best distance runners come from places like rural Kenya, where they often spend their formative years running without shoes—a circumstance that heavily predisposes them not to land on their heels. If they’re fast enough, however, they’ll get a shoe sponsor and start receiving cushioned shoes that may make them more likely to switch to a heel strike. If that happens, are they succeeding because of or despite the way they land?
One of the most commonly cited articles on this topic comes from Japan back in 2007. At a large half marathon, three-quarters of the runners were heel-strikers—but only 62 percent of the top 50 finishers were heel-strikers, suggesting that faster runners were less likely to land on their heels. There’s a problem with reading too deeply into this, though. The fastest runners were also probably more likely to be wearing singlets from running clubs, but no one would suggest that those singlets actually make you faster.
With that preamble, here’s what Hanley and his colleagues found in the 71 men and 78 women they studied. Overall, about 60 percent of the men and 70 percent of the women were heel-strikers. Most of the rest of midfoot strikers, which they defined as “the heel and midfoot, or occasionally the entire sole, contacted the ground together.” Only a handful were pure forefoot strikers.
The proportions varied a bit from lap to lap, ranging from 54 percent heel strikers in the first lap of the men’s race to 73 percent in the fourth and final lap of the women’s race. More than three-quarters of the athletes kept the same foot strike throughout the race, and those that did change were most likely to go from midfoot to heel—consistent with earlier evidence that your ankles, which work harder when you land on your forefoot, are more likely to tire before your knees and hips.
Here’s what the progression looks like in visual form for the women’s race, with the number of runners with RFS (rearfoot strike), MFS (midfoot strike) and FFS (forefoot strike) for each lap shown, along with the small number of changes from lap to lap.
You could argue that the proportion of rearfoot strikers did increase throughout the race (a pattern that’s perhaps a little more pronounced in the men’s data). Certainly fatigue does seem to push people more in that direction. But overall, the researchers were surprised at how consistent the runners were.
One final point of interest is a comparison between those finishing in the top half of the field and those finishing in the bottom half. After all, we want to model ourselves on the Eliud Kipchoges of the world, not the admirable but well-beaten Ruritanian champion. In this analysis, there was no difference between the faster and slower men. In fact, the top four finishers (from Kenya, Ethiopia, Tanzania, and Great Britain) landed on their heels throughout the race. There was, however, a glimmer of difference in the women’s race: by the final lap, 87 percent of the bottom 50 percent of finishers were landing on their heels, significantly more than the 59 percent in the top half.
The conclusion, in some sense, is that there isn’t one. That’s not an empty statement, because the lack of an obvious pattern is pretty significant. To be clear, this doesn’t prove that foot strike has no effect. But it puts an upper bound on the size of the effect: if most of the best marathoners in the world are doing something, it can’t be that bad. “These findings suggest there is no one optimal foot-strike pattern with regard to performance,” the researchers conclude, “and athletes should not be overly encouraged to alter what comes naturally to them.”
My new book, Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, with a foreword by Malcolm Gladwell, is now available. For more, join me on Twitter and Facebook, and sign up for the Sweat Science email newsletter.