Walking on your heels gives you longer ‘virtual limbs’! A new study explains why humans walk on their heels instead of their toes; the paper is published in The Journal of Experimental Biology.
Humans have a ‘heel-first walking’, as opposed to many other organisms in the animal kingdom (cats and dogs, for instance) who use the balls of their feet. Why is this so? Could this constitute a certain advantage for humans, asked a researcher from the University of Arizona, James Webber. The latter, together with his colleague, David Raichlen, wanted to dig deeper into the heel-to-toe stride of humans.
This subtle trait of ours has made of us incredible walkers. Otherwise, efficient walkers throughout the animal world are characterised by long legs, something which we don’t have (relatively speaking). But, this apparent problem is countered by our heel-first stride—we, thus, don’t need to have long legs, explains Webber.
“Humans are very efficient walkers, and a key component of being an efficient walker in all kind of mammals is having long legs,” says Webber. “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 we’re up on our toes, and this was a conundrum to us (scientists).”
So, while our legs are shorter than other efficient walkers, our walking strategy caters for the same effect—Webber describes the the heel-first walking as ‘giving’ us longer, ‘virtual’ limbs.
Webber goes further into such analogies: according to him, the walking movement of humans resembles an inverted swinging pendulum—the body oscillates above the point of meeting of the foot and the ground. As we walk forward, the center of pressure slides from heel to toe, and the true pivot for the inverted pendulum is situated at midfoot, few centimeters below the ground, such that an overall effect of longer virtual legs below the ground is produced—virtual limbs longer than our physical ones.
“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,” says Webber.
As for the unnatural toe-first stride, it would make us move slower, with a greater need for efforts (up to 10% more). Our normal heel-first walking actually gives us 15 centimeters more, thanks to the ‘additional limbs’.
“The extra ‘virtual limb’ length is longer than if we had just had them stand on their toes, so it seems humans have found a novel way of increasing our limb length and becoming more efficient walkers than just standing on our toes,” adds Webber. “It still all comes down to limb length, but there’s more to it than how far our hip is from the ground. Our feet play an important role, and that’s often something that’s been overlooked.”