How humans got their walk decoded

Human feet are more mobile than those of chimpanzees, say scientists who used high-speed motion capture to measure and compare 3D foot movements to decode how our foot structures enables us to walk upright.
Researchers from New York Institute of Technology questioned some long-held ideas about the function and evolution of the human foot by investigating how chimpanzees use their feet when walking on two legs.
Most researchers studying human evolution assume a stark dichotomy between human and chimpanzee feet. One is a rigid lever that makes walking long distances easy and efficient.
The other one is a grasping device, much more mobile and less effective at walking on two legs. Fossil feet of early human ancestors are nearly always compared with chimpanzee feet, making knowledge of their foot biomechanics crucial for understanding how the human foot evolved.

However, prior to this research, no one has been able to actually investigate whether differences existed between humans and chimpanzees in how the foot works during walking on two legs.
To find out, researchers used high-speed motion capture to measure three-dimensional foot motion in chimpanzees and humans walking at similar speeds. They then compared ranges of mid-foot motion between species.

Contrary to expectations, the researchers found that human feet are more - not less - mobile than chimpanzees walking on two limbs.
"This finding upended our assumptions about how the feet of both humans and chimpanzees work. Based on simple visual observation, we've long known that human feet are stiffer than those of chimpanzees and other apes when the heel is first lifted off the ground in a walking step," said Nicholas Holowka from Harvard University in the US.

"What surprised us was that the human midfoot region flexes dramatically at the end of a step as the foot's arch springs back into place following its compression during weight-bearing," said Holowka.
"This flexion motion is greater than the entire range of motion in the chimpanzee mid foot joints during a walking step, leading us to conclude that high mid foot joint mobility is actually advantageous for human walking," Holowka added.
"We never would have discovered this without being able to study chimpanzees with advanced motion capture technology," Holowka added.
Ultimately, according to the findings, the fact that the traditional dichotomy between humans and chimpanzees has been disproven means that researchers may have to rethink what can be learned from the fossil feet of humans' earliest ancestors.

The study appears in the Journal of Human Evolution.