Has a Norwegian Physicist Shown That All Elites Run Wrong?

Let me start by answering the question in the title: No. No, he hasn’t. You’re welcome to click away to another page, but since theories like this seem to be remarkably persistent, I’ll take a few minutes to look at the claims.

A Norwegian physicist and a Finnish physiologist just published a paper in the Proceedings of the Royal Society of London, UK called “Gravity-driven horizontal locomotion: theory and experiment,” and it was picked up by New Scientist. The basic idea is that, as you fall forward with each stride, you gain energy from gravity, and if you adjust your stride in a specific way you can carry this extra boost of energy from one stride to the next. As a result, you can reduce your running cost by about 10 percent, resulting in an improvement of one to two minutes over 10K.

But wait, there’s more! You can apply this same technique to walking, allowing you to walk “without any muscular effort”—just coasting along with gravity pushing you forward like some sort of perpetual motion machine. Even better, you can carry heavy loads and walk uphill with no additional effort, all thanks to gravity.

So what do you need to do to get these wonderful benefits? The basic gist is that you have to make sure your foot lands below your center of mass, rather than in front of it, so you can preserve the angular momentum generated by gravity when you lean forward. The paper presents the theory with a bunch of equations, then some experimental results showing how well it works.

The main bit of experimental data comes from a “49-year-old veteran male runner who had over the years become able to do relatively well on angular momentum-assisted running”—in other words, a pal of the author. They have him run on a treadmill at various speeds with his gravity stride or a “normal” stride (which isn’t further described), and sure enough he consumes lower energy with the gravity stride. Frankly, I’d like to see what his “normal” stride looked like, since he’s clearly a convert to the new technique.

They also tested four other distance runners with the new technique. All of them consumed “either similar or even significantly increased energies” with the gravity stride; their data, for some reason, isn’t shown. One sprinter apparently shouted “I’m flying!” with great enthusiasm while running with the new stride; but his data isn’t shown either.

The rest of the data is similarly skewed or incomplete. The oxygen-consumption results for gravity-driven walking didn’t reveal the predicted minimum at a speed corresponding to “no muscular effort,” so they show instead the data for total air exhaled—a more or less meaningless parameter in this case, but one that happens to have the shape they’re looking for. This is called data-mining.

As for the theoretical stuff, this idea has been around for a while. Some may remember an infamous 2007 paper by Pose founder Nicholas Romanov called “Runners do not push off the ground but fall forwards via a gravitational torque,” which was effectively rebutted by a commentary in a subsequent issue by researchers from Massey University in New Zealand. It appeals to the same gut feeling: everyone knows what it feels like to be pulled forward by gravity as you fall—so wouldn’t it be great to harness that same force with every stride you take?

In a sense, of course, gravity does play a very important role in running. Without gravity, as the Massey response points out, “after the first stride you would be somersaulting backwards and travelling away from the support surface indefinitely.” And the new paper is not wrong in arguing that overstriding causes you to waste energy. But the claim that gravity—a force directed straight downward—gives you free energy to help travel in a forward (much less uphill) direction is simply wrong.

The new paper is pretty vague and hard to wade through, but as far as I can tell it makes a couple of key blunders. The basic picture it presents is the following, with the runner represented as a point of mass rotating about a fixed point:

It’s clear that, in this picture, you gain an amount of rotational energy that corresponds exactly to the gravitational energy lost by descending a distance delta h. Can you carry this energy through to the next stride without losing any? Yes—but only if you magically get shorter by delta h with each stride. In reality, you need to raise your center of mass back up to its original height to start the next stride. Doing so will require exactly the amount of energy that you “gained” from gravity in the first place.

The paper claims (without ever explaining why) that this doesn’t matter, because they’re interested in momentum as well as energy. And indeed, at the moment before you lift your foot off the ground, you’re rotating forward (counterclockwise in this picture). But again, notice that by the time the next stride starts, you’re upright again: your body has rotated clockwise while in the air, meaning that you applied a torque in the opposite direction as you pushed off. As previous studies have shown, we do a very good job at keeping overall angular momentum close to zero throughout the gait cycle. Whether you’re talking about energy or momentum, everything balances out, and there’s no free lunch.

One thing I’ll give the authors credit for is that they at least tried to test their ideas experimentally. Both running and walking remain enormously complex actions that are the topic of ongoing scientific debate and discussion; no one claims to have all the answers about how it works. That’s why, in the end, the proof of the pudding is in the eating.

As the New Scientist article reports, the lead author “believes training distance runners and sprinters to run in this fashion would shave minutes off race times, resulting in a rash of new records.” Show me that, and perhaps I’ll reconsider my faith in the basic laws of physics.

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