Human Evolution Linked to Flexible Foot Arch

FIGURE . (A) The center of mass (COM) propulsion hypothesis suggests that both arch recoil and foot leverage can elevate COM. (B) Foot levers around the metatarsophalangeal joint’s fulcrum.

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Scientists have discovered that the kick created by the flexible arch of human feet helps place our legs in the optimal posture for advancing bipedal walking. Understanding how our joints help modern humans walk upright could help us track the evolution of bipedalism and improve care for patients with foot problems.

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 walking 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 recoil repositions the ankle upright for more effective walking. The effects on running are larger, suggesting that the ability to run efficiently could have been a selective pressure for a flexible arch that also made walking more efficient. This discovery could even help doctors improve treatments for foot problems in today’s patients.

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

Step by Step

The evolution of our feet, including the high medial arch that differentiates us from great apes, is crucial for bipedal walking. The bow is thought to give hominids more strength when they walk upright: the mechanism is unclear, but when the movement of the bow is restricted, running demands more energy. Arch recoil could potentially make us more efficient runners by driving the body’s core mass forward or by offsetting the mechanical work the muscles would otherwise have to do.

To investigate these hypotheses, the team selected seven participants with variable arch mobility, who walked and ran while their feet were filmed by high-speed X-ray motion capture cameras. Each participant’s arch height was measured and a CT scan of the right foot was performed. The scientists created rigid models and compared them to the measured movement of the bones of the foot 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 the center of mass and propulsion of the ankle.

Leaning towards bipedalism

Although the scientists expected to find that arch recoil helped the rigid arch lever lift the body, they found that a rigid arch without recoil caused the foot to lift off the ground earlier, which likely decreased the efficiency of the arch muscles. calf, or tilted the ankle bones too far forward. The forward lean reflects the posture of walking chimpanzees, rather than the upright posture characteristic of human walking. The flexible arch helped reposition the ankle upright, allowing the leg to lift 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 bow.

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

"The mobility of our feet appears to allow us to walk and run upright rather than leaning forward or taking the next step too soon," said lead author Dr. Michael Rainbow of Queen’s University.

Therapeutic potential

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 bow to move during propulsion makes movement more efficient,” Welte said. "If we restrict the movement of the arch, there are likely to be corresponding changes in the function of the other joints."

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

Applications

Enabling plantarflexion mobility of the arch has many important applications, including footwear design, understanding pathology, and surgical practice. Certain footwear modifications, such as increasing the flexural rigidity of the shoe sole or using inserts that restrict the arch, reduce plantar flexion of the arch and may respectively modify the muscular contractile conditions of the ankle during locomotion or increase the cost of metabolism. operating at ground level.

Our results also have implications for people with naturally stiff feet or foot pathologies (such as osteoarthritis) that reduce mobility in the arch. When the tarsal joints are surgically fused, ankle power decreases during walking, further suggesting that a mobile arch supports ankle propulsion. Our method could also be used to predict dynamic motion patterns in surgical joint fusions. By mathematically fixing the joints in known positions, we can elucidate possible changes along the kinematic chain. For example, we would expect fusion of the cuneonavicular joint to substantially impair propulsion, causing the foot to lift off the ground earlier or increasing force requirements at the ankle. These results highlight the importance of preserving arch mobility in surgical practice and shoe design.