These feet were made for walking

February 26, 2020

Many of us take our feet for granted, but they have a challenging job in the biomechanics department. When we push off with the ball of the foot, the force we apply exceeds our body weight, causing the middle of the foot to bend. Yet the foot maintains its shape because it is stiff enough to withstand this force. Researchers have long debated what gives the midfoot its stiffness. Now, a new study, published in Nature, has shed light on the importance of a little-studied structure called the transverse arch (TA), which runs across the foot.

"Having a firm understanding of how the human foot works has several real-world applications," said Professor Mahesh Bandi, from the Nonlinear and Non-equilibrium Physics Unit at the Okinawa Institute of Science and Technology Graduate University (OIST), who co-led the study. For example, he explained, the current definition of flatfoot disorder is solely based on the well-studied medial longitudinal arch (LA), which runs the long way down the foot, and doesn't consider the transverse arch (TA). What's more, he adds, this research could also help with the design of robotic feet and point to clues about how bipedal walking evolved.

Previous studies have found that 25% of the foot's stiffness is conferred by the LA. The researchers theorized that the TA contributes even more to this effect, much like how rolling a floppy piece of paper makes it harder to bend. Using a protocol developed with the help of computer simulations, and experiments on plastic and mechanical models, the researchers found that about half of the stiffness in human cadaveric feet is controlled by the TA.

Measuring the stiffness of the human foot

To determine what influences midfoot stiffness, Professor Bandi and colleagues created both computer simulations and plastic models of the midfoot and measured how much force was required to bend them a certain amount.

"We found that the plastic models and simulations with more pronounced TAs were stiffer and less susceptible to bending than flatter ones," said Professor Bandi. "In contrast, on these models, an increase in the curvature of the LA had little effect on the stiffness."

They then performed bending tests on mechanical models of the foot, which varied in length, thickness and TA curvature. As with the simulations and plastic models, they found that the mimics with more pronounced TAs were stiffer to bend. Finally, they found that cutting the TA tissues in feet from human cadavers donated to research - while leaving the LA tissues intact - reduced the feet's stiffness by about a factor of half.

In the steps of our ancestors

Professor Bandi and colleagues also looked at the role the TA played in human evolution. Researchers know that the feet of vervet monkeys, macaques, chimpanzees and gorillas are substantially flatter than human feet, and can only partially stiffen. Meanwhile, species within the genus Homo, like us, all have a pronounced TA, enabling effective walking and running.

By comparing the curvature of the TA in humans and non-human primates to fossils of earlier hominin species, Professor Bandi and colleagues measured where a prominent TA first appeared in the fossil record. "Our findings suggest that a human-like TA predates the genus Homo by around 1.5 million years and was a vital component in the evolution of modern humans. This shows that in future tests, researchers need to analyze both arches, not just the LA," said Professor Bandi.

This research was jointly led by Professor Bandi, Professor Madhusudhan Venkadesan from Yale University and Professor Shreyas Mandre from the University of Warwick. It was funded by a Young Investigator Grant from the Human Frontier Science Program.

Okinawa Institute of Science and Technology (OIST) Graduate University

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to