Finding efficiency in the weird way we walk

You probably haven’t thought too hard about how to walk since you were a toddler, but that doesn’t mean that the human stride is a simple concept. The fact that each of our steps lands on our heel is actually a strange trait, since most animals handle everything on the balls of their feet, with their heels never touching the ground. As humans are fairly efficient walkers, scientists have been looking for ways that we might benefit from such an unusual stride.

Part of what makes heel-first walk so strange is that it goes against concepts understood to help make an animal walk with more efficiency. When other animals walk with their heels up, they’re orienting their skeleton to effectively have a longer leg, and longer legs are more efficient per step than shorter ones. So by stepping on our heels, we’re essentially shortening the possible length of our leg, which should be a waste of energy.

Looking past our legs

Researchers think that the answer may be to look beyond our actual legs, and focus on the overall arch of motion. When we step, we rock our weight from heel to the middle of our foot, which makes our leg move over our foot like an inverted-pendulum. However, by starting on the heel, the true center of this pendulum motion isn’t right at our foot at ground level. To swing our leg forward from the back of our foot, the true fulcrum point would be about six inches below the ground.

This sort of “virtual leg” length seems to make real biomechanical difference. In a lab, people asked to walk by landing on the front of their feet had to work 10 percent harder than people walking with their normal stride. Only once you change your gait to more of a run (when barefoot) does landing on the balls of your feet begin to make sense again.

Pedestrians of times past

Our ancient ancestors didn’t always move exactly like this. Based on fossilized footprints from 3.6 million years ago, early bipeds landed on their heels, but with relatively larger, stiffer feet. They were probably very efficient walkers, but not great runners. It’s suggested that modern humans’ shorter toes and feet likely evolved to help us get off our heels and run, which we’re actually better at than you might think, and not just because of our toes.

Source: Why we walk on our heels instead of our toes, Scienmag