An extra spring helped humans run and walk upright

2023-05-30 11:20:30

(A) The Center-of-Mass (COM) Propulsion Hypothesis Suggests That Both Bow Recoil And Foot Leverage Can Elevate COM. (B) The Foot Levers Around The Metatarsophalangeal Joint From The Point Of Support. – WELTE ET AL./FRONTIERS

MADRID, 30 May. (EUROPA PRESS) –

An international team of scientists has shown that humans could have evolved a spring-like bow to help us walk on two feet.

Researchers studying the evolution of bipedal gait have long assumed that the high arch of the foot helps us walk by acting as a lever that propels the body forward. But a global team of scientists has now discovered that Flexible arch kickback repositions the ankle upright for more efficient walking.

The effects on running are greater, suggesting that the ability to run effectively might have been a selective pressure for a flexible arch that also made walking more efficient. This discovery, presented in ‘Frontiers in Bioengineering and Biotechnology’it could even help doctors improve the treatment of foot problems for current patients.

“At first we thought that the elastic arch helped lift the body for the next step,” explains Lauren Welte, Ph.D., first author of the study and now at the University of Wisconsin-Madison. It turns out that the spring-like arc moves back to help the ankle lift the body instead.”

The evolution of our feet, including the raised medial arch that sets us apart from great apes, is crucial to bipedal gait. The bow is thought to give hominins more leverage when walking upright: the mechanism is unclear, but when bow movement is restricted, running requires more energy.

The recoil of the arc could make us more efficient runners, propelling the core mass of the body forward or compensating for the mechanical work that the muscles would otherwise have to do.

To investigate these hypotheses, the team recruited seven participants with varying arch mobility, who walked and ran while their feet were filmed by high-speed X-ray motion capture cameras. The arch height of each participant was measured and images were taken of their right foot.

The scientists created rigid models and compared them to the measured movement of the foot bones to test the effect of arch mobility on adjacent joints. They also measured which joints contributed the most to arch recoil and the contribution of arch recoil to ankle center of mass and propulsion.

Although the scientists expected that arch recoil would help the stiff arch lever lift the body, they found that a stiff arch with no recoil would cause the foot to leave the ground early, probably decreasing the effectiveness of the muscles of the foot. calf, or tilted the ankle bones too far forward.

The forward lean reflects the chimpanzee walking posture, rather than the upright posture characteristic of human gait. The flexible arch helped bring the ankle back upright, allowing the leg to come off the ground more effectively. This effect is even greater when running, suggesting that gait efficiency may have been an evolutionary pressure in favor of the flexible arch.

The scientists also discovered that the articulation between two bones of the medial arch, the navicular and the medial cuneiform, is crucial for the flexibility of the arch. Changes in this articulation could help us trace the development of bipedalism in the hominin fossil record.

“The mobility of our feet seems to allow us to walk and run upright instead of bending over or taking the next step too soon,” explains Dr Michael Rainbow, from Queen’s University (Canada) and lead author of the study.

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

“Our work suggests that allowing the arch to move during propulsion makes movement more efficient,” Welte says. “If we restrict the movement of the arch, it is likely that corresponding changes in the function of the other joints will occur.” “.

“At this stage, our hypothesis requires further testing because we need to verify that population-wide differences in foot mobility lead to the types of changes we see in our limited sample,” Rainbow said. That said, our work lays the foundation for an exciting new avenue of research.”