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The paper, “Foot Strike Patterns and Collision Forces in Habitually Barefoot Versus Shod Runners,” provides evidence that modern cushioned running shoes actually change the body's natural gait in a way that can lead to injuries such as tibial stress fractures and plantar fasciitis.
Davis's co-authors on the paper include researchers from Harvard University, University of Michigan Medical School, Providence Veterans Affairs Medical Center in Rhode Island, Moi University Medical School in Kenya, and University of Glasgow in the U.K.
The researchers compared foot strike kinematics among five groups of runners, including three categories of adult subjects -- habitually shod athletes from the U.S., Kenyan athletes who grew up running barefoot but now wear cushioned shoes, and American runners who grew up wearing shoes but now run barefoot or in minimal footwear -- as well as two groups of adolescents, one of barefoot runners who have never worn shoes and the other of runners who have worn shoes most of their lives.
The researchers found that the habitually barefoot endurance runners from Kenya typically strike the ground with the forefoot, referred to as fore-foot strike (FFS), or the mid-foot (MFS). In contrast, the habitually shod American athletes were more likely to land on the heel, referred to as rear-foot strike (RFS).
RFS, which results from the elevated heel on the shoes, generates greater collision forces than the FFS and MFS associated with barefoot running. The forces travel up the body and may cause impact-related injuries to the feet and lower legs.
“Differences between RFS and FFS running make sense from an evolutionary perspective,” the paper states. “If endurance running was an important behavior before the invention of modern shoes, then natural selection is expected to have operated to lower the risk of injury and discomfort when barefoot or in minimal footwear. Most shod runners today land on their heels exclusively. In contrast, runners who cannot or prefer not to use cushioned shoes with elevated heels often avoid RFS landings and thus experience lower impact transients than do most shod runners today, even on very stiff surfaces.”
The paper represents the work of a truly interdisciplinary group of researchers, including not only physical therapy and biomechanics but also engineering, biomedical and life sciences, and evolutionary biology.
Last year, Davis began to collaborate with Harvard's Dan Lieberman, lead author on the paper, because of a common interest in barefoot and minimal footwear running and their complementary areas of research expertise.
“Dan is a human evolutionary biologist whose research is focused on why we evolved to run and how we ran before shoes,” Davis says. “I am a clinical biomechanist who has been studying the relationship between running biomechanics and injury, and how this relationship might be altered when running barefoot. This overlap in interest provided a natural synergy that has been very exciting for both of us.”
The two are planning a trip to Kenya during the summer of 2010 to conduct a more extensive mechanical analysis of the habitually barefoot runners.
Head of the University of Delaware Running Research Laboratory, Davis conducts research on the relationships among lower extremity structure, mechanics and injury during human locomotion. She is particularly interested in helping runners improve their mechanics so that they can run pain free.
A runner herself, Davis has been widely quoted in the popular media recently on the issue of barefoot running. Christopher McDougall, author of the best-selling book Born to Run, has referred to her as “a barefoot skeptic turned convert.” She is now logging about 20 miles per week on asphalt and has found that it doesn't hurt. “The harder the surface,” she says, “the more lightly you land and the more easily you spring back.”
“The way in which this has all come together has been such a perfect storm,” Davis says. “In my studies of running injuries, I have found that the impact transient associated with heel strike is associated with injury. As a result, we have been developing a novel gait retraining intervention using real-time feedback to reduce this loading in shod runners.”
She continues, “We also know that when individuals take their shoes off and run, they avoid a heel strike because it hurts. This suggests that our heel pad was not designed to attenuate the loads of impact during running. One could argue that it is because we wear shoes all the time and our heel has adapted to this. However, our work with Kenyans who have never worn shoes further substantiates our hypothesis, as they also avoid heel striking when they run. Shoes encourage a rear-foot strike pattern, as runners can increase their stride length and land on their heels. But they pay for it with an impact peak that we weren't designed for.”
The research reported in the paper was funded by the National Science Foundation, the American School of Prehistoric Research, the Goelet Fund, Harvard University and Vibram USA.
Published weekly, Nature is the world's most highly cited interdisciplinary science journal. Articles covering all fields of science and technology are selected for publication on the basis of “originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions.”
Article by Diane Kukich
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