We may be lousy runners compared to other animals, but we sure can hold our own in a fight.
- Humans and other great apes all walk heel first, the most energy-efficient way to walk.
- Great apes are relatively aggressive animals, and foot posture benefits fighting.
- Humans are also built for long-distance walking and running, but not sprinting.
Heel to toe is by far the most efficient way for people to walk, according to new research that zeroed in on the mechanics of the human gait.
And as for why we evolved to walk heel to toe? It could have been to make it easier to fight for territory or mates, says the study's lead researcher.
Heel-first walking is extremely rare in the animal kingdom, with bears and great apes among the few animals that share this gait with humans. Most other mammals, such as dogs, cats and raccoons, walk and run on the balls of their feet. Speedy ungulates, like horses and deer, run and walk on tiptoes.
Humans, bears and other apes have this behavior in common, and we are all "relatively aggressive" animals, lead author David Carrier told Discovery News.
"Plantigrade feet, in which the heel makes contact with the ground, allow large torques to be applied to the ground," explained Carrier, a professor of biology at the University of Utah. "Animals with this foot posture are able to apply larger forces to opponents during fighting that involves wrestling and possibly also larger forces during striking with the forelimbs."
"Male orangutans, gorillas and chimpanzees all compete for access to females," he added, "fighting in ways that often result in serious injury or death."
For the study, published in the Journal of Experimental Biology, Carrier and his colleagues had volunteers -- mostly 20- to 40-year-old athletes -- walk in three different ways: on tiptoes, ball first and heel first. The volunteers wore masks that allowed the scientists to study oxygen consumption, a measure of energy expended.
The tests found that, compared to heel-first walkers, those who stepped first on the balls of their feet used 53 percent more energy. Those who stepped toe first expended 83 percent more energy.
Further analysis determined that heel-first walking reduces the up and down motion of the body's center of mass, making it easier on the hips, knees and ankles. It also provides more leverage and uses overall energy more efficiently.
When the volunteers ran, on the other hand, their gait didn't matter in terms of energy expenditure; they could step heel or ball first and use about the same amount of energy.
"Lots of elite athletes, whether sprinters or distance runners, don't land on their heel," said Carrier. Many of them run on the balls of their feet, as do people who run barefoot. That appears to be the natural ancestral condition for early human runners."
Another recent study, led by Evie Vereecke of the University of Liverpool's School of Biomedical Sciences, determined that gibbons run like human track stars.
"We found that gibbons hit the ground with their toes first, similar to the forefoot strike of professional sprint runners, which stretches the tendons in the toes," she said.
Since our primate ancestors had the same basic foot design while still living in the trees, economy of running and walking probably doesn't explain why humans evolved their ways of moving. That could get back to our aggressive tendencies.
When our ancestors left the trees, Carrier said hunter-gatherers would establish large home ranges and travel six to nine miles per day, sometimes while carrying heavy loads of provisions. The pace would quicken, he explained, if the individual was engaged in persistence hunting, "in which the human hunter kept prey animals running for long periods in the heat of the day until the prey collapsed from heat exhaustion."
These hunters were barefoot, and Carrier believes "the best shoes for walking and running are no shoes." But, for those of us who don footwear, he said "it makes sense to avoid stiff-soled shoes that result in a slapping landing of the foot on the ground."