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hubie [soylentnews.org] writes:

Scientists have discovered that the recoil created by the flexible arch of human feet helps position our legs in the optimal posture for moving forward in bipedal walking [frontiersin.org]:

A new study has shown that humans may have evolved a spring-like arch to help us walk on two feet. Researchers studying the evolution of bipedal [frontiersin.org] walking have long assumed that the raised arch of the foot helps us walk by acting as a lever which propels the body forward. But a global team of scientists have now found that the recoil of the flexible arch repositions the ankle upright for more effective walking. The effects in running are greater, which suggests that the ability to run efficiently could have been a selective pressure for a flexible arch that made walking more efficient too. This discovery could even help doctors improve treatments for present-day patients' foot problems.

"We thought originally that the spring-like arch helped to lift the body into the next step," said Dr Lauren Welte, first author of the study in Frontiers in Bioengineering and Biotechnology [frontiersin.org], who conducted the research while at Queen's University and is now affiliated with the University of Wisconsin-Madison. "It turns out that instead, the spring-like arch recoils to help the ankle lift the body."

The evolution of our feet, including the raised medial arch which sets us apart from great apes [frontiersin.org], is crucial to bipedal walking. The arch is thought to give hominins more leverage when walking upright: the mechanism is unclear, but when arch motion is restricted, running demands more energy. Arch recoil could potentially make us more efficient runners by propelling the center mass of the body forward, or by making up for mechanical work that muscles would otherwise have to do.

[...] Although the scientists expected to find that arch recoil helped the rigid lever of the arch to lift the body up, they discovered that a rigid arch without recoil either caused the foot to leave the ground early, likely decreasing the efficiency of the calf muscles, or leaned the ankle bones too far forward. The forward lean mirrors the posture of walking chimpanzees, rather than the upright stance characteristic of human gait. The flexible arch helped reposition the ankle upright, which allows the leg to push off the ground more effectively. This effect is even greater when running, suggesting that efficient running may have been an evolutionary pressure in favor of the flexible arch.

[...] "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," said Dr Michael Rainbow of Queen's University, senior author.

These findings also suggest therapeutic avenues for people whose arches are rigid due to injury or illness: supporting the flexibility of the arch could improve overall mobility.

Journal Reference:
Lauren Welte, Nicholas B. Holowka, Luke A. Kelly, et al., Mobility of the human foot's medial arch helps enable upright bipedal locomotion [open], Front. Bioeng. Biotechnol., Volume 11 - 2023 | https://doi.org/10.3389/fbioe.2023.1155439 [doi.org]

Original Submission