There’s been quite a bit of talk lately about a new study that came out early in the month, Metabolic Cost of Running Barefoot versus Shod: Is Lighter Better?, by Jason R. Franz, Corbyn M. Wierzbinski, and Rodger Kram. You can see one of the stories at Barefoot Running Less Efficient.
I’ve taken a bit of a look at the study.
The way these studies work is that they put special masks on their runners that measure both oxygen used and carbon dioxide produced. From those levels you can tell how much energy the body burned, and then comparisons can be made.
It is already generally acknowledged in the literature that for about every 100 grams of extra weight on the foot, you burn about 1% more energy. Thus, most folks thought that removing the shoe entirely would be the most efficient.
This study seems to show otherwise, and my big question was, why?
The study itself notes that there have been seven previous studies. Five of those found NO difference in oxygen burned. Two of the studies did find a difference, with one in particular, Oxygen Cost of Running Barefoot vs. Running Shod, by N. J. Hanson, et al. finding a 5.7% difference, with barefoot running being more efficient.
This latest study notes, however, that the previous studies did not control for a lot of factors, such as foot-strike pattern, barefoot running experience, and shoe construction). So they tried to do so as much as possible. They made sure that all their runners they tested had barefoot running experience. They made sure that all their runners used a mid-foot strike. When they wore footwear, they all wore Nike Mayflies, very lightweight shoes. When I first read the study, I figured they were something like a Vibram with an extremely flexible sole, since they had no arch support or any motion control features. But that was not the case. Here’s a picture of the Nike Mayfly:
Those are pretty thick soles: 14 mm.
And then they compared it to barefoot running. OK, I guess I should have said “barefoot” running, because the subjects were not really barefoot. As the study says:
For the duration of the experiment, subjects wore very thin, slip-resistant yoga socks for safety and hygienic purposes.
Huh? Geez, I hate those sorts of comments and hidden (wrong) assumptions. First, exactly what hygienic purpose is needed. Yes, they were running on a treadmill, but exactly how is hygiene implicated. And how do they provide safety? Were they afraid people were going to be strewing nails on their treadmill?
But there’s more. They were also wearing a foot harness. They actually cut down the uppers of a running shoe to have a place to attach their weights. Here’s what the “barefoot” runners were really wearing:
As their description says
To add mass to each foot during barefoot trials, we modified the uppers of a running shoe to allow for easy attachment of small lead strips while still simulating barefoot running. We removed the outsole, midsole, and the entire front portion of the shoe upper, anterior to the midshaft of the fifth metatarsal, leaving only the heel counter, thin fabric arch section, tongue and laces.
So, what was going on? I suppose it is possible that the “barefoot” contraption was causing problems and that led to the “barefoot” running being less efficient. But there is also something else in the study.
They took careful pictures and noted that the “barefoot” runners stride was about 3% shorter than the shod stride. That could account for the efficiency difference. But as I already pointed out, we don’t really know why the stride was shorter. Maybe the socks, even though “slip-resistant” didn’t feel slip-resistant, so the runners took shorter steps. Or, it could be that the heavy cushioning in the shoe allowed them to slap down their feet harder, as one is forced to do with a longer stride. One also has to consider the idea that this longer stride, and slap-down, might be generating increased stresses on the joints.
Oh, and what about that other study (the Hanson study) that showed barefoot running to be more efficient? Let me say a couple of things about that. That study actually had their runners run outdoors (“overground” is the term used). That 5.7% difference is overground. On treadmills, the Hanson study found only a 2% gain in barefoot running over shod. I can see how there really might be a difference under real, outdoors running conditions.
But not so fast. As Franz pointed out, Hanson’s study may have been flawed in the way they measured speed, particularly outdoors. They did so with a very fancy pedometer, but one that would have missed differences in speed due to stride-length. See Is Barefoot Running More Economical?. It’s hard to believe, though, that they wouldn’t have checked their speed results more closely, and in the end, while they calibrated their device, nobody really knows just what those devices do.
I’d say that the answer is still in doubt. From this study, it is plausible that barefoot running without the cushioning of the shoe, even if both are mid-foot striking, is less efficient due to a shorted stride length. But I don’t think they are there yet. I’d like to see more studies that forced even more uniformity and eliminated (and isolated) these other factors.
But there is one more thing I’d like to point out.
If I’m going for efficiency, I’m going to put on my inline skates. If I’m not out to win a marathon (or am on the edge of collapse from trying to win one), the efficiency difference probably doesn’t make a difference.
Otherwise, I’m going for tactile sensations and fun.
[Note: there's another good write-up on the study at Runner's World.]