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Shoe-wearing runners have adapted their gait to their footwear, according to a recent study led by Harvard evolutionary biologist Daniel E. Lieberman ’86 and published in Nature magazine.
The study examines how runners coped with the force of collision on their feet before the introduction of the modern running shoe in the 1970s. Comparing habitually barefoot runners with shoe-wearing runners, Lieberman and his fellow researchers found that runners who run with footwear tended to land on their heels, while runners who run barefoot tended to land on the front or middle parts of their feet.
Because humans do not have rigid bodies, only a certain percentage of human body mass—called effective mass—can feel the force of an impact.
According to Lieberman, runners who strike the ground with their heels feel four times as much collisional force as runners who strike the ground on the front or middle parts of their feet.
This difference is due to the rigidity of the ankle when a runner lands vertically.
“It’s a pretty simple idea, basic Newtonian physics: force equals mass times acceleration,” he said.
Lieberman used the dropping of pen on a table as an analogy to illustrate the differences in impact.
“When you drop [the pen] vertically, the whole pen is the mass that comes to a dead stop,” he said. “When you drop it on a 45 degree angle, the collision is much less noisy, because part of the pen’s translational energy is converted to rotational energy.”
In Lieberman’s study, data from the barefoot runners actually came from subjects who habitually ran without shoes. Previous studies on the barefoot running debate did not take into consideration that subjects in the barefoot group habitually ran with shoes as well and therefore were more likely to have a heel strike.
Lieberman said that he was prompted to think about the issue of how barefoot runners were able to run long distance for millions of years without the aid of shoes after he gave a speech before the start of the Boston Marathon. A man who was wearing only duct tape around his socks had insisted on asking Lieberman difficult questions about running.
The duct tape runner, Harvard alumnus Jeffrey T. Ferris ’77, became Lieberman’s first subject.
—Staff writer Gautam S. Kumar can be reached at firstname.lastname@example.org.
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