This page will be populated with frequently asked questions as we encounter questions that need our responses.
Where can I find videos related to your work?
Please see the channel on YouTube for associated videos.
What are the most important findings of the study?
Our study is the first to show that a previously overlooked arch in the foot is a major part of its stiffness. It is a case of “new tricks for an old pony.” Everyone knew that our feet have two major arches. Everyone also knew that the uniquely arched shape of human feet is important for its stiffness. But no one thought to look at the transverse arch that runs along the width of the foot and instead only studied the longitudinal arch that runs along its length. We found that the transverse arch is a bigger source of stiffness than the longitudinal arch. We also discovered that the transverse arched evolved to become almost human-like over 3.5 million years ago. This changes the picture for how the human foot evolved, and probably played a big part in us becoming bipedal.
Why is foot stiffness important?
Our feet apply large forces on the ground every time we walk or run. These forces can be several times our body weight, and at push-off, most of the force is concentrated on the front of the foot, known as the ball of the foot. In order for us to push in this manner, it is important for the foot to maintain its shape. That is the role of stiffness, a property that helps to maintain shape.
How does this research benefit people’s health?
Our research does not directly address health but it opens new ways to study the foot for future researchers on foot health. Fundamental thinking in how the foot’s shape affects its mechanical stiffness should be changed. Basic things like definitions of flatfoot are based upon the longitudinal arch and do not consider the transverse arch. Our work throws these standard practices into question but more work is needed to know how to update them.
How does this research change what we know about evolution?
All the older research has focused on the longitudinal arch to assess whether the feet of our ancestors could have helped them walk or run like us. Although everyone knew about the gradual evolution of the transverse arch, no one looked into it any deeper. Because of our new discovery on the transverse arch, we looked deeper and found that a human-like transverse arch evolved much before the direct ancestors to humans, known as genus Homo, appeared on the scene. We are not talking just slightly before, but a good 1.5 million years before genus Homo. This may explain why there are preserved footprints dating back to that period that look a lot like humans, although no other species had a human-like longitudinal arch at that time. It is probably the transverse arch that resolves these apparent inconsistencies! But we cannot directly test the stiffness of these ancient and extinct species. So, caution is needed in these interpretations and more fossils need to be discovered for gaining a better understanding.
Where are the two arches?
The TTA runs across the width of the foot and located around its middle along the length. Our feet have long ray-like bones called metatarsals that run from the middle of the foot to the toes. These are similar also to the bones of the palm, from wrist to knuckles. The metatarsals are arranged so that they are level with the ground towards the front of the foot. But near the middle of the foot, they are raised from the ground and arranged in an arched shape. The transverse tarsal arch, TTA for short, is formed by the raised end of the metatarsals. The medial longitudinal arch, MLA for short, runs from the heel to front. That longitudinal arch is more pronounced on the side of the foot facing the other foot, known as the medial side.
Is a stiffer foot better?
It is not that simple. Better for what is the real question. A stiffer foot will undoubtedly be better at withstanding greater forces. But the foot is a living organ and does more things than just hold its shape. In running, for example, the foot behaves like a spring that stores energy and recoils to provide an assistive boost. A stiffer foot would not be good at storing energy this way. But understanding which elements of the foot contribute to stiffness is essential. Only then can we know how muscles and other elements may change the stiffness of the foot depending on what it is used for.
Will an arched foot help me run faster? Be more energy-efficient, etc?
These are great questions and remain open to further research. What our work shows is that the TTA is an integral part of future studies.
Can I make my foot stiffer by cupping it?
Cupping your foot is tricky! But say you could do that. That alone may not mean higher stiffness. As our study with the cadaveric feet and the mechanical mimics showed, the interplay between the transverse arch and elastic tissues in between the metatarsals is important for stiffness. Having curvature without the tissues is of no use. Neither is having strong tissues without curvature. How such things play out when cupping the foot remains to be seen.
Should I be buying curved shoes?
Our study does not test the effect of shoes or external attachments. Understanding the interaction between the foot and shoe is a research question that is being pursued by many groups around the world. So, we cannot recommend anything specific about footwear.
What advice do we give readers who suffer from flatfoot disorders?
Our work raises the question of what is a flatfoot. Because of our findings on the TTA, how to define flatfoot needs more careful examination. More studies and data are the way to go. There are a lot of people in the world whose feet appear flat with respect to the MLA but have no difficulty walking. Such asymptomatic flatfeet and diversity in foot shape could be important for studying how the MLA and TTA interact. These will ultimately feed into what is even a disorder that needs treatment, and what sort of treatment could be effective.
I thought stiffness is bad, as in being stiff because of a lack of training.
The word stiffness could have multiple meanings. We are using it to refer to the property of materials to resist being stretched. Think of a spring. Try to stretch it and it will pull you back with some force. Greater the stretch, greater the force. The ratio between the force and stretch is called stiffness.
Is all the past research wrong because they studied the wrong arch?
Far from it. We have built upon the findings over the past century. Our work draws insights from many fields. We use mathematical analysis and physics to recognize that the TTA may be important. We use methods in engineering to build and test mimics of the foot. Anatomy and medical science play an important part in conducting studies on cadaveric feet. The importance of body donors is huge. They allow such discoveries to happen. Data, samples and methods from palaeontology and physical anthropology allowed us to learn how the TTA evolved. Such an effort is not unlike the African proverb that says that “it takes a village to raise a child.”
However, our research has added a new dimension to the understanding of the foot and its evolution. Like many scientific advances, it opens new avenues to be explored.
Will cupping my hands make it stiffer so that I can walk using my hands?
Ha! That is a curious question. In 1995, Glasheen and McMahon studied how running using your arms compare to using your legs. This is not a light question. It begins to tell us what changes may have happened to the upper body because we evolved to become bipedal. But no one (including us) has looked at the hand and what curvature may do.
Should I tell my podiatrist to change my current orthotic?
Our paper is not a medical paper. I urge caution in not over-interpreting our findings or taking hasty actions. Always consult a medical expert before making such changes and certainly wait before future research addresses questions of how the TTA affects foot function in those with disorders or injuries.
My feet look flat, but I am OK otherwise. Should I be concerned?
Nothing needs to change as a result of our work alone. If you were consulting a medical professional about it, continue to do so.