Finally, to test whether being barefoot and having calluses do affect how people move, Dr. Lieberman and his collaborators asked some of the Kenyans to walk unshod over a plate that measures forces generated while striding. The plate registered almost no variations in their strides, whether they had thick calluses or none.
But back in Boston for the final element of the study, the researchers found that shoes can shake up a walk. When male and female volunteers strolled on treadmills at Dr. Lieberman’s lab while barefoot, they struck the ground in about the same way as the unshod walkers in Kenya had.
But when those same volunteers donned average, cushioned sneakers, their walking subtly altered. They began striking the ground a little more lightly at first, presumably because the footwear’s cushioning absorbed some of the force, but the impacts from each stride lingered longer than when they were barefoot.
Such persistent impacts tend to move up and dissipate through our leg bones, ankles and knee joints, whereas the shorter, sharper jolts created when we walk barefoot are more likely to rise through our soft muscles and tendons, Dr. Lieberman says.
What these findings suggest, in aggregate, is that what we wear on our feet shapes the way that we walk, and that nature would make a fine footwear engineer, Dr. Lieberman says. Shoes protect our feet and sop up some of the slight pounding during a walk, he says, but they also alter our strides and could, over time, increase the pressure and wear on our leg joints. Meanwhile, calluses shield us from some of the discomforts and pointy objects we encounter while barefoot, but do not reduce our contact with and feel for the ground.
So, the message of the study would seem to be that people who have concerns about their balance or their knees but not their pedicures might consider sometimes walking barefoot, he says.
“Walking barefoot can be fun,” he says, although it is not for everyone or every situation. When winter ends and warmth returns to Harvard, he often sheds his shoes and encourages new calluses, he says. “But I wear shoes most of the time.”
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