Photo

Phys Ed Gretchen Reynolds on the science of fitness.

Barefoot-running enthusiasts long have believed that running without shoes or in minimalist footwear makes running easier, speedier and less injurious. But a surprisingly large number of new studies examining just how the body actually responds when we run in our birthday shoes or skimpy footwear suggest that for many people, those expectations are not being met.

Consider, for instance, the findings of the most definitive of the new studies, published last month in The Journal of Applied Physiology. It looked into whether landing near the front of the foot when you run is more physiologically efficient than striking the ground first with the heel.

This is a central issue in any discussion of barefoot-style running, because one of the supposed hallmarks of running shoeless or in minimalist footwear is that doing so promotes a forefoot landing. Without the heel cushioning provided by standard running shoes, barefoot proponents say, runners will gravitate naturally toward landing lightly near the balls of the feet.

And they should, most proponents add, because landing near the front of the foot will require less oxygen and effort and allow you to push harder at any given speed and ultimately run faster or longer.

But that idea, while appealing, has not been well scrutinized. So researchers at the University of Massachusetts Amherst recruited 37 experienced runners, 19 of whom were habitual heel-strikers and 18 of whom landed first near the front of the foot. (Heel striking is far more common than forefoot striking among modern runners, by most estimates, with at least 70 percent of us nowadays leading with our heels.)

The researchers began by outfitting all of the volunteers with the same neutral running flats and then having each run on a treadmill as he or she normally would, using his or her preferred foot strike. The volunteers ran at three different speeds, equivalent to an easy, middling and fast pace. Throughout, the researchers measured oxygen uptake, heart rates and, through mathematical calculations, the extent to which carbohydrates were providing energy.

Then, in a separate experiment, they asked each runner to switch styles — the heel-strikers were to land near the balls of their feet and the forefoot strikers with their heels — while the researchers gathered the same data as before.

In the end, this data showed that heel-striking was the more physiologically economical running form, by a considerable margin. Heel strikers used less oxygen to run at the same pace as forefoot strikers, and many of the forefoot strikers used less oxygen — meaning they were more economical — when they switched form to land first with their heels.

Most of the runners also burned fewer carbohydrates as a percentage of their energy expenditure when they struck first with their heels. Their bodies turned to fats and other fuel sources, “sparing” the more limited stores of carbohydrates, says Allison Gruber, a postdoctoral fellow at the University of Massachusetts Amherst, who led the study. Because depleting carbohydrates results in “hitting the wall,” or abruptly sagging with fatigue, “these results tell us that people will hit the wall faster if they are running with a forefoot pattern versus a rear-foot pattern,” Dr. Gruber says.

These findings undermine some of the entrenched beliefs about minimalist shoes or barefoot running, but they jibe closely with the conclusions of multiple studies presented last week at the annual meeting of the American College of Sports Medicine in Indianapolis. Five separate studies there found no significant benefits, in terms of economy, from switching to minimalist, barefoot-style footwear.

The news on injury prevention and barefoot-style running is likewise sobering. Although many barefoot-style runners believe that wearing lightweight shoes or none at all toughens foot muscles, lessening the likelihood of foot-related running injuries, researchers at Brigham Young University did not find evidence of that desirable change. If foot muscles become tauter and firmer, the scientists say, people’s arches should consequently grow higher. But in a study also presented at the sports medicine meeting, they found no changes in arch height among a group of runners who donned minimalist shoes for 10 weeks.

Other researchers who presented at the meeting had simply asked a group of 566 runners if they had tried barefoot-style shoes and, if so, whether they liked them. Almost a third of the runners said they had experimented with the minimalist shoes, but 32 percent of those said that they had suffered injuries that they attributed to the new footwear, and many had switched back to their previous shoes.

None of this new science, of course, proves that barefoot-style running is inadvisable or disadvantageous for all runners; it proves only that the question of whether barefoot is best is not easily answered. “There are lots of individual instances where people report that change” from one type of running shoes or running form to another “was good for them,” says Rodger Kram, a professor of integrative physiology at the University of Colorado at Boulder, who’s long studied running form. “There are also lots of cases of people switching or trying to switch who got hurt.”

The primary lesson of the accumulating new science about barefoot-style running, he says, is that “the biomechanics of running are not simple, and generic proclamations” — like claims that all runners will benefit from barefoot-style shoes and running form — “are surely incorrect.”

Dr. Gruber agrees. “I always recommend that runners run the way that is most natural and comfortable for them,” she says. “Each runner runs a certain way for a reason, likely because of the way they were physically built. Unless there is some indication that you should change things, such as repeated injury, do not mess with that plan.”