Researchers reporting in the Jan. 28 issue of the journal Nature show that runners who run without shoes usually land on the balls of their feet, or sometimes flat-footed, compared to runners in shoes, who tend to land on their heels first.
Cushioned running shoes, which date back only to the 1970s, may seem comfortable but may actually contribute to foot injuries, according to Daniel Lieberman, professor of human evolutionary biology at Harvard University, and his colleagues.
The scientists, using motion and force analyses, showed that barefoot runners who strike on the fore-foot (land on the balls of their feet) generate smaller collision forces than shod rear-foot strikers.
The researchers say that although there are anecdotal reports of reduced injuries in barefoot populations, more work is needed to test their view that either barefoot runners or those with minimal footwear (such as sandals or moccasins) have reduced injury rates.
Running Barefoot Can Be Comfortable
By running on the balls of the feet or the middle of the foot, runners avoid more forceful impacts, equivalent to two to three times of body weight, that shod heel-strikers repeatedly experience.
"People who don't wear shoes when they run have an astonishingly different strike," Lieberman says in a news release. "By landing on the middle or front of the foot, barefoot runners have almost no impact collision, much less than most shod runners generate when they heel-strike.
"Most people today think barefoot running is dangerous and hurts, but actually you can run barefoot on the world's hardest surfaces without the slightest discomfort and pain."
He says a few calluses can help runners avoid injuries.
Build Up to Barefoot Running
Lieberman and colleagues analyzed the running styles, or gaits, of five groups of people:
• U.S. adult athletes who had always worn shoes
• Kenyan adult runners who grew up barefoot but now wear cushioned running shoes
• U.S. adult runners who grew up wearing shoes but now run barefoot or with minimal footwear
• Kenyan adolescents who have never worn shoes
• Kenyan adolescents who have worn shoes for most of their lives.
And they say they found a striking pattern.
Most shod runners, which would encompass 75 percent or more of Americans, strike their heels when they run, experiencing a large and sudden collision force an average of 960 times for every mile they run, making runners prone to repetitive stress injuries, the authors write.
On the other hand, people who run barefoot tend to land with a step toward the middle or front of the foot, causing less impact force to the foot.
Madhusudhan Venkadesan, a co-author and researcher in applied mathematics and human evolutionary biology at Harvard, says in the news release that heel-striking is painful when running barefoot or in minimal shoes "because it causes a large collisional force each time a foot lands on the ground."
But barefoot runners point their toes more at landing, avoiding the collision effect by decreasing the "effective mass of the foot that comes to a sudden stop when you land, and by having a more compliant, or springy leg."
Modern people have grown up wearing shoes, so running barefoot is something to be eased into, Lieberman says. Modern running shoes are designed to make heel-striking easy and comfortable. He suggests runners who want to shed their shoes do so slowly to build strength in the calf and foot muscles.
By Bill Hendrick
Reviewed by Louise Chang
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