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Biomechanist Irene Davis, Ph.D., has been a leading researcher in the running field for more than 20 years. In recent years, she has particularly focused on demonstrating that runners can change their form--it was previously thought that running form was as innate and immutable as a fingerprint. She next hopes to show that proper running form can reduce risk of injury. Unlike some scientists, Davis is an unabashed promoter of barefoot running and barefoot-like running form.

“I believe there is a compelling body of evidence that suggests we need to consider a paradigm change," she told me yesterday. "But paradigm changes are risky, and younger scientists may be more tentative."

A University of Delaware professor for many years, Davis has recently taken a new position in the Department of Physical Medicine and Rehabilitation at Harvard Medical School as director of the Spaulding National Running Center that she is developing. At next week's American College of Sports Medicine meeting in Denver, she'll be part of a symposium panel titled, "Barefoot Running: So Easy a Caveman Did It!"

I asked her several questions about abstracts she and her colleagues will be presenting in Denver, and also about her current thoughts on barefoot running.

Runner's World: In one of your form-changing studies, you apparently found that runners could reduce tibial shock by either landing more on their midfoot or forefoot, or by landing further back on their heels. Those results seem sort of contradictory.
Irene Davis: Indeed, Brad Bowser, lead author, and I were surprised to see the increased rearfoot strike. We had hypothesized that they would reduce the tibial shock by transitioning to more of a forefoot landing. But we didn't instruct the runners how to reduce their loading – we allowed them to adopt their own strategy as we were interested in how they would do it. And it appears that more runners adopted the greater rearfoot strike pattern.
Here's what I think happened: I think most of them utilized the rearfoot strategy as it was their accustomed pattern. Instead of changing to a midfoot or forefoot strike, they just accentuated it more and sort of rolled through their foot strike.

In another one of  your abstracts, you reported that barefoot runners had very similar loading rate patterns to shod runners with a midfoot strike. The big winners, in terms of lower loading rates, were the shod runners who used a distinct forefoot strike. So the barefoot runners didn't appear to gain any big benefit.
Yes, Allison Altman and I had hypothesized that the loading rates of the barefoot runners would be similar to the shod forefoot strikers. But what happened was that five of our subjects had very high load rates in the barefoot condition. That drove the overall average higher than we expected. None of these five were habitual barefoot runners and when we further analyzed the data, we found that these five subjects actually landed on their heels. This is very unusual for barefoot runners and creates very high load rates--even higher than heel striking in shoes! When these subjects data are removed, the mean values for barefoot are nearly identical to the shod FFS, as we expected.This is explained in the poster that we'll present in Denver, but there wasn't enough space in the abstract to include it.

Published: May 27, 2011 12:00 AM EDT?
An interesting study was reported last year at the American Society of Biomechanics (ASB) investigating the effect of socks on single leg balance. It was determined that a thin pair of socks causes a statistically significant reduction in balance, suggesting that they filtered out important sensory information. We will be reporting on a related study at the upcoming ASB meeting looking at dynamic stability during a single leg landing in bare feet, Vibrams, and Nike Air Pegasus.

The causes of running injuries seem so hard to identify. It's even hard to define "injury." Do you think we're ever going to make any real progress understanding why injury rates are so high today?
You have made the comment, and it is true, that today's runners may be very different from those in the past--we have many more less fit people running. So, admittedly, it is difficult to compare today’s injury patterns with those of 40 years ago. What we need are more studies that make comparisons between different groups of runners of today. Yes, I think these could be done in a way that produces meaningful statistical data.

Why isn't anyone studying barefoot running and landing styles on different surfaces? We've got a lot of hard asphalt out there today.
There have been numerous studies that have looked at how runners react to different surfaces. We now know that runners will change their form in just one or two strides when they hit a hard surface like concrete or a soft surface like sand. They'll adapt a softer landing on concrete, and a stiffer landing on sand. This applies to shoes as well. It has been shown that runners stiffen their knee when landing in cushioned shoes compared to bare feet, even though those shoes reduce impacts when tested in a lab. Things change dramatically when you interface the shoes with a runner who has a complex, well-honed, sensory feedback system.

I'm not an evolutionary biologist, but when I talk to evolutionary biologists,like Dan Lieberman, they tell me that we did evolve to run on hard surfaces, and that  the African savannah was quite hard. It may not be as hard as pavement, but I believe we have an innate ability to adapt to whatever surfaces we come in contact with. So, with reasonable time to adapt, I think we have the potential to run well on hard surfaces. Every stride you take running barefoot on a hard surface will give you a lower loading rate than running with a rearfoot strike in shoes. In addition, you don't want to take away the sensory feedback mechanism, and that's what shoes do.