Friday, March 30, 2012

#GretchenReynolds reports on the metabolic cost of barefoot running.

Correction Appended

Does it take more work to run in sneakers or barefoot?Jordan Siemens/Getty ImagesCan a sneaker improve your performance?
Phys Ed

For the past few years, proponents of barefoot running have argued that modern athletic shoes compromise natural running form. But now a first-of-its-kind study suggests that, in the right circumstances, running shoes make running physiologically easier than going barefoot.

The study, conducted by researchers at the University of Colorado in Boulder, began by recruiting 12 well-trained male runners with extensive barefoot running experience. “It was important to find people who are used to running barefoot,” says Rodger Kram, a professor of integrative physiology, who oversaw the study, which was published online in the journal Medicine & Science in Sports & Exercise.

“A novice barefoot runner moves very differently than someone who’s used to running barefoot,” Dr. Kram says. “We wanted to look at runners who knew what they were doing, whether they were wearing shoes or not.”

Specifically, he and his colleagues hoped to determine whether wearing shoes was metabolically more costly than going unshod. In other words, does wearing shoes require more energy than going barefoot?

A few previous studies have suggested that in terms of physiological effort, it’s easier to go barefoot. After all, shoes have mass; they add weight to your feet, and pushing weight through space, as you do with every step while running, demands energy.

These earlier studies generally concluded that every additional 100 grams (or about 3.5 ounces) added to your feet should increase the energy cost of running by about 1 percent. Over many miles, that 1 percent becomes magnified if you wear heavy running shoes, which can easily weigh 300 to 400 grams or more.

But for the new study, Dr. Kram and his colleagues wanted to use a relatively lightweight, cushioned shoe. They chose the Nike Mayfly, a model that, as the name intimates, is a flyweight, barely reaching 150 grams.

The runners were asked to run multiple times on treadmills while either wearing the shoes or not. The runners were never completely barefoot; when unshod, they wore thin yoga socks to protect them from developing blisters and for purposes of basic hygiene on the shared treadmills.

Next, the researchers taped 150 grams’ worth of thin lead strips to the top of runners’ stockinged feet. By adding an equal amount of weight to the bare foot, they could learn whether barefoot running really was physiologically more efficient than wearing shoes.

It wasn’t. When barefoot runners and shod runners carried the same weight on their feet, barefoot running used almost 4 percent more energy during every step than running in shoes.

To the surprise of the researchers, barefoot running, often touted by fans as more natural than wearing shoes, was actually less efficient.

“What we found was that there seem to be adaptations that occur during the running stride that can make wearing shoes metabolically less costly,” says Jason R. Franz, a doctoral candidate at the University of Colorado who led the study. Shoes, he says, “provide some degree of cushioning.” If you eschew shoes, “something else has to provide the cushioning.”

That something, he and his colleagues believe, is your legs. If you are barefoot, the job of absorbing some of the forces generated by the collision of foot and ground shifts to your leg muscles, a process that Dr. Kram calls the “cushioning effect.” As a result, the leg muscles contract and work more and require additional energy. The metabolic cost of the activity rises.

Of course, most barefoot runners don’t head out to jog wearing leaded Band-Aids, as they did in this study. But notably, even when unweighted barefoot running was compared foot-to-foot with running in the Mayflies, the shoes won out. For 8 of the 12 runners, wearing shoes remained slightly more efficient than being barefoot, even though the shoes added more weight.

It’s important to note that the study looked only at the metabolic efficiency of wearing shoes, compared with going barefoot. The scientists didn’t evaluate the common claim that barefoot running lowers injury risk.

In the end, the difference in metabolic cost between going barefoot or wearing lightweight shoes is probably of greatest interest to competitive runners. Serious racers might want to mull over the trade-off between having less mass on their feet when barefoot versus having greater potential strain on their leg muscles.

For the rest of us, the lesson might be that even if you’re not interested in going barefoot, you might want to invest in a slimmed-down trainer. “There is a metabolic cost to wearing really heavy running shoes,” Dr. Franz says. Lightweight models, though, that provide cushioning to spare leg muscles without mass to slow movement may be the physiologically smartest alternative, he says, to being bare.

Correction: March 21, 2012

An earlier version of this post misstated the weight of running shoes, which may easily weigh 300 to 400 grams, not ounces.

My take home message from this study is their results are consistent with my testing on myself, that I'm a bit faster and more comfortable with a bit of padding underfoot, but not much and the flatter the shoe the better. CSS and I just got the scale out and my Minimus, VFFs and Free 3.0's are all well under 200 g, and I have some Hattori's coming for tri season which are about 150 g. CSS loves his Hattori's, which seem to be a great compromise between low weight, no heel lift and some cushion underfoot (as well as appearing to be tri-perfect with the velcro closure and sock upper).

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