• Posted May 31, 2023

The Arch of the Human Foot Was Key to Upright Walking, Scientists Say

That happy, confident spring in your step is likely a benefit imparted by human evolution, a new study argues.

Humans may have evolved a spring-like arch in our feet to help us better walk and run upright, researchers say in their study, published May 30 in the journal Frontiers in Bioengineering and Biotechnology.

It's long been assumed that the raised arch of the foot helps us walk by acting as a lever that propels the body forward, researchers said in background notes.

But a global team of scientists have now found that the recoil of the flexible arch also repositions the ankle upright for more effective walking.

This recoil provides more aid in running, which suggests that people evolved a flexible arch to help them run more efficiently, researchers said. That it also helps walking is an added bonus.

"We thought originally that the spring-like arch helped to lift the body into the next step,"lead researcher Lauren Welte, a postdoctoral fellow at the University of Wisconsin-Madison, said in a journal news release. "It turns out that instead, the spring-like arch recoils to help the ankle lift the body."

The evolution of human feet was crucial to the ability to walk upright, and that includes the raised medial arch which sets us apart from great apes, researchers said.

The arch is thought to give humans more leverage when walking upright, researchers said. That's not clear why exactly, but it's been shown that when a person's motion is restricted, running demands more energy, researchers said.

Arch recoil could potentially make us better runners by propelling our center mass forward, or by aiding the muscles in the mechanical work of movement.

To investigate these hypotheses, the research team filmed seven participants with varying arch mobility, using high-speed X-ray motion capture cameras as the people walked and ran. The height of each participant's arch was measured, and their right foot was scanned by CT.

The researchers then created rigid models of arches and compared them to the motion of the foot bones observed through these recordings, to test the effect of arch mobility on adjacent joints.

The team also measured which joints contributed the most to arch recoil, and the contribution of arch recoil a person's propulsion.

The scientists had expected to find that arch recoil helped the rigid lever of the arch to lift the body up.

But they found that a rigid arch without recoil either caused the foot to leave the ground early or leaned the ankle bones too far forward. This created a posture that mirrored walking chimpanzees, rather than a characteristic upright human stance.

"The mobility of our feet seems to allow us to walk and run upright instead of either crouching forward or pushing off into the next step too soon,"study co-author Michael Rainbow, of Queen's University in Kingston, Canada, said in the release.

It turns out that the flexible arch helps reposition the ankle upright, which allows the leg to push off the ground more effectively, researchers concluded. The effect is even greater in running, which suggests that the ability to run better promoted the evolution of the flexible arch.

Researchers also found that a joint between two bones in the medial arch, the navicular and the medial cuneiform, is crucial to the arch's flexibility. By tracking changes to this joint in fossils, future research might be able to better the development of bipedalism in humans.

These results also suggest potential therapies for people whose arches are rigid due to injury or illness, researchers said. Anything that supports the flexibility of the arch could improve a person's overall mobility.

"Our work suggests that allowing the arch to move during propulsion makes movement more efficient,"said Welte. "If we restrict arch motion, it's likely that there are corresponding changes in how the other joints function."

The researchers said further testing is needed in a larger sample.

More information

Johns Hopkins Medicine has more about foot problems.

SOURCE: Frontiers in Bioengineering and Biotechnology, news release, May 30, 2023