Humans Walk Weird

Bionic Power

Staff Writer

You may not realize it, but humans have a weird way of walking. Biomechanists have broken down the logistics in a single step into several phases: touchdown, where your heel hits the floor. Following that is the single support phase of balancing on that one leg. Finally, you roll onto your toes for takeoff, sending the leg into a forward swing. Researchers have also observed a distinct “double-bounce” that occurs when we walk. This happens when our planted leg bounces twice before entering the third phase of gait, meaning our knees flex twice over the course of a single step. Over the next few days, we’ll be sharing the findings of scientists at the University of Munich. Their study has uncovered the mystery behind our double-bounce gait pattern, which is an energy-saving technique that prioritizes endurance over speed.

The human foot is an oddity in the animal kingdom. Not only do we have a 90-degree angle between the foot and the leg, but our legs are also considerably heavy relative to the rest of our bodies, a combination of features unique to humans. Where most animals walk on their tiptoes or balls of their feet, humans walk heel-to-toe. There may be an evolutionary explanation for this. In order to have the strength to propel our bodies forward, we’ve had to trade off speed for endurance.

Running gait Vs Walking

When we run, we do so with a single bounce pattern as opposed to the unique double-bounce gait we observe during walking. This is because running is a mostly airborne motion, unlike walking, which requires that we stabilize ourselves. When we walk, our foot remains on the ground for a majority of the step cycle, around 70%, to maintain stability at slower speeds. However, this results in less time to push ourselves forward. This paradoxically means that the body needs to exert more effort to move the leg for the next step. It may seem counterintuitive to aim for a walking pattern that leaves little time to move the leg forward because of the weight of our legs, as more mass requires more energy.

Breaking Down Our Weird Walk and How We Got Here

Mechanical engineers propose that nature has found a clever workaround for the limitations of the human body design. The foot remains on the ground for as long as possible to maintain balance, but during that time, the ankle stores energy for release. This is similar to a catapult, where a heavy object – the upper body – holds the ankle down and the more it is pulled back, the stronger the subsequent forward release. Researchers have found that the second bounce in our gait, when the knee bends just before the foot takes off, provides the final push for the ankle to fling the leg into the next step.

How does this tie back to our evolutionary past? This method of walking would have been beneficial for early humans during persistence hunting – chasing animals until they became too exhausted. As our flat feet and heavy legs are not optimized for speed, it’s possible that our gait evolved to allow us to cover greater distances instead. The second bounce in our gait, which propels the leg from the ankle, uses less energy than powering the swing from the hip, allowing our ancestors to stalk prey for extended periods without needing to rest.

Thanks for tuning in to our Humans Walk Weird series! We hope you enjoyed learning about these findings as much as we enjoyed sharing them.

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