SALT LAKE CITY — Humans, bears and apes have the greatest advantage of all the mammals when it comes to walking around, according to the latest University of Utah research.
It takes less energy to walk the way we do, planting our heels first rather than running around on tiptoes like horses and deer, or on the balls of feet like dogs, cats, raccoons and most of the rest of mammalia.
"You consume more energy when you walk on the balls of your feet or your toes than when you walk heels-first," said David Carrier, U. biology professor and author of the study.
The economics of walking was studied by analyzing 27 volunteer athletes in their 20s, 30s and 40s, each of whom walked and ran three different ways to determine which methods expound the least and most energy from the body. Researchers measured oxygen consumption, using a mask on the subjects, as well as a force plate on the ground to measure forces exerted by the body in movement.
The findings are available online at jeb.biologists.org and will be printed in the March 1 issue of The Journal of Experimental Biology.
Compared with heels-first walkers, those stepping first on the balls of their feet used 53 percent more energy, and those stepping toes-first expended 83 percent more energy.
Carrier and other researchers found that the activity of the major muscles of the ankle, knee, hip and back all increase when people walk on the balls or toes of their feet.
"That tells us that the muscles increase the amount of work they are producing if you walk on the balls of your feet," he said, adding that in walking on the balls of our feet, we end up taking shorter, more frequent strides. Walking heel-first lengthens our stride because it uses the entire length of the foot.
Walking heel-first, however, is not more economical because it is more stable or involves fewer, longer strides, but because when we land on our heels, less energy is lost to the ground, we have more leverage, and kinetic and potential energy are converted more efficiently.
And while humans have cornered the market on walking, other animals have adapted more for running.
"They've compromised their economy of walking for the economy of running," Carrier said.
When people run, he said, for unknown reasons, there is no difference in the amount of energy they expend when stepping first onto their heels versus the ball of their feet or tiptoes.
"If you land on your heel when you run, the force underneath the foot shoots very quickly to the ball of your foot," he said. "Even when we run with a heel plant, most of the step our weight is supported by the ball of our foot."
Many elite athletes, he said, run on the balls of their feet, the same as people who run barefoot, which is what early human runners did.
"The important thing is we are remarkable, economical walkers," Carrier said. "We are not efficient runners. In fact, we consume more energy to run than the typical mammal our size. Be we are exceptionally economical walkers."
It seems that humans are built for walking.
"The whole foot contacts the ground when we walk," Carrier said, adding that humans have a big heel and a big toe, which is more robust and parallel to and right next to the second toe, that is as long as our other toes.
"These features are distinct among apes, and provide the mechanical basis for economical walking," he said. "No other primate or mammal could fit into human shoes."