The secrets of the human foot deciphered

The remarkable bipedalism of man is largely due to his feet. These are strong enough to support the weight of the body and act as real springs when walking. Scientists have just uncovered its secret, which could have consequences in health, robotics and even for shoe manufacturers.

The foot is a surprisingly complex structure. It includes no less than 26 bones that hold together thanks to 33 joints and about 100 muscles, ligaments and tendons. It is also he who supports the whole body weight and gives us our excellent ability to walk, run or jump. A team of researchers has just discovered the secret of these extraordinary capacities: the longitudinal arch of the foot, in other words the curvature of the foot arch which connects the first metatarsal calcaneus, in the heel.

A real spring underfoot

For their study, published on February 26 in the journal Nature, Madhusudhan Venkadesan, of Yale University, and his Japanese and American colleagues, dissected human corpses to analyze the role of each tendon. In a living subject, the number of forces applied to the foot is so large that it is indeed impossible to isolate the role of each element individually. According to their tests, the longitudinal arch alone is responsible for 40% of the rigidity of the foot. " The ligaments that cover the arch of the foot act as a bowstring to resistcollapse of the arch when a force is applied, and the mechanical properties of these ligaments look like springs, making a substantial contribution to storing and returning theenergy to push ", Detail the authors. When the tendon is cut, we also observe a 50% drop in stiffness. However, the transverse arch (which runs horizontally across the top of the foot between the two metatarsals), would play an at least as important role in preventing the foot from twisting. " It's like a slice of pizza that stiffens when the crust outer is rolled up "Illustrates Madhusudhan Venkadesan, the main author of the study.

The bending of the foot, a key factor in bipedalism

" The rigidity of the human foot, which allows effective thrust when walking or running, has been essential to the evolution of bipedalism, explain the researchers. This morphology arched in the middle of the human foot makes it more rigid, while others primates have flat feet that flex strongly in the middle ". The appearance of a sufficiently curved arch, around 1.8 million years ago, undoubtedly played a key role in the development of bipedalism and the ability of man to move and run, estimate Researchers.

The curvature of the transverse arcs in humans nevertheless covers a wide range of values, some people have almost flat feet while others have a very raised arch. We know that people with flat feet (collapsed arch) suffer from hip and knee problems, periostitis of the tibia, with ankle instability, pains feet and calluses. They also tire faster when walking. " It is nevertheless possible that some people with flat feet have sufficient transverse curvature to compensate for their low longitudinal arch, thus retaining sufficient rigidity to walk and run effectively. Notes Madhusudhan Venkadesan.

Prostheses, bipedal robots and shoes

For researchers, the role of the transverse arch has been notoriously underestimated in the study of human evolution, but also in the sports sciences and medicine. Study Expected to Develop New Treatments for Various pathologies foot, but also prostheses better suited or bipedal robots more able to walk. Shoe manufacturers, who are struggling to sell us perfectly flat sneakers and sneakers, should also be affected.

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