Now, a small but growing body of research suggests that barefoot is the way adults should run, too. So, many runners have been shucking off the high-tech trainers in favor of naked feet — or minimalist footwear like Nike Free, the Newton All-Weather Trainer and the glove-like Vibram FiveFingers.

"People have been running barefoot for millions of years and it has only been since 1972 that people have been wearing shoes with thick, synthetic heels," said Daniel Lieberman, a professor of human evolutionary biology at Harvard University.