Why do humans walk with a heel-to-toe stride, while other animals walk on the balls of their feet? A new study, published in the Journal of Experimental Biology, may provide some answers.

In addition, why do barefoot runners land in the middle or balls of their feet rather than their heels when they run, which would feel unnatural while walking?

“Humans are very efficient walkers, and a key component of being an efficient walker in all kind of mammals is having long legs,” says James Webber, a researcher from the University of Arizona, in a media release.

“Cats and dogs are up on the balls of their feet, with their heel elevated up in the air, so they’ve adapted to have a longer leg, but humans have done something different. We’ve dropped our heels down on the ground, which physically makes our legs shorter than they could be if were up on our toes, and this was a conundrum to us (scientists),” Webber adds.

In essence, Webber states, heel-first walking creates longer “virtual legs.”

“Humans land on their heel and push off on their toes. You land at one point, and then you push off from another point eight to 10 inches away from where you started. If you connect those points to make a pivot point, it happens underneath the ground, basically, and you end up with a new kind of limb length that you can understand. Mechanically, it’s like we have a much longer leg than you would expect,” Webber explains.

In the study, Webber and his adviser and co-author, UA anthropologist David Raichlen, monitored study participants on a treadmill in the University’s Evolutionary Biomechanics Lab. They looked at the differences between those asked to walk normally and those asked to walk toe-first. They found that toe-first walkers moved slower and had to work 10% harder than those walking with a conventional stride, and that conventional walkers’ limbs were, in essence, 15 centimeters longer than toe-first walkers.

When they sped up the treadmill to look at the transition from walking to running, they also found that toe-first walkers switched to running at lower speeds than regular walkers, further showing that toe-first walking is less efficient for humans, per the release.

“When you’re running, if you have a really long foot and you need to push off really hard way out at the end of your foot, that adds a lot of torque and bending,” Webber states. “So the idea is that as we shifted into running activities, our feet started to shrink because it maybe it wasn’t as important to be super-fast walkers. Maybe it became important to be really good runners.”

[Source(s): University of Arizona, EurekAlert]