Writing in the journal Nature, they said runners who wear shoes tend to hit the ground with their heels first, whereas barefoot runners put the balls of the feet down first.
"People who don't wear shoes when they run have an astonishingly different strike," Lieberman said in a statement.
"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," Lieberman added.
"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. All you need is a few calluses to avoid roughing up the skin of the foot."
Lieberman and his colleagues at Harvard, the University of Glasgow, and Kenya's Moi University studied runners who had always run barefoot, those who had always worn shoes and runners who had abandoned shoes.
Barefoot runners had a springier step overall, and used their calf and foot muscles more efficiently, they found.
Demonstrations can be seen here.
People used to running in shoes should not start barefoot trotting right away, Lieberman cautioned. "If you've been a heel-striker all your life, you have to transition slowly to build strength in your calf and foot muscles," he said.
But he noted that evolution is on his side.
"Humans have engaged in endurance running for millions of years, but the modern running shoe was not invented until the 1970s," Lieberman said. Rival German companies Adidas and Puma made running shoes a household item.
Running shoes are big business. Nike Inc had $4.4 billion in revenue in its second quarter.
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