Dr Michelle Dickinson: Nanotechnologist on the new research showing bigger feet aren't just bigger versions of small feet

Have you ever wondered whether people with big feet just have larger versions of the same foot structure as those with smaller feet?  

New research published in Royal Society Open Science took a deep dive into how human feet change shape with size, and the results were surprising.

The researchers studied the two largest bones in the human foot, the talus (which connects the foot to the leg) and the calcaneus (better known as the heel bone). They gathered 3D computed tomography (CT) scans from 36 adults, covering a range of foot sizes. Then, they used advanced statistical modelling to examine how these bones' shapes and surfaces scaled with size. 

If big feet were just larger versions of small feet, their bones would scale isometrically, meaning that all dimensions would grow at the same rate. However, if the bones changed shape as they got bigger, they would be scaling allometrically, adapting their proportions to accommodate different stresses and forces. 

The results showed that while the talus scaled pretty much as expected (meaning it grew proportionally in all directions), the calcaneus did something different. Instead of just getting larger, it became more cube-like as foot size increased. The researchers found that as the heel bone got bigger, it became taller, wider, and shorter in length relative to its size. This means that big feet are not just enlarged copies of small feet, their bones actually shift in shape to better handle stress and pressure. 

Interestingly, the joint surfaces of the calcaneus, where it connects with other bones, grew at a faster rate than the rest of the bone. This suggests that larger feet need bigger contact areas at the joints to distribute pressure more effectively, reducing stress and potential injury. 

Understanding how foot bones scale can have major implications for medicine, biomechanics, and even footwear design.  

Next time you look at your feet, or someone else's, you can appreciate that they might be very different to your own.

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Episode Transcript

Speaker 1 (00:06):
You're listening to the Sunday Session podcast with Francesca Rudgin
from News Talks EDB.

Speaker 2 (00:13):
Joining me now with our science study of the week
is doctor Michelle Dickinson.

Speaker 3 (00:16):
Good morning, Good morning.

Speaker 2 (00:18):
This one is fascinating.

Speaker 3 (00:20):
I don't know how we didn't know this already.

Speaker 2 (00:23):
Well, why would you presume that they're any different? You
just think, somemer, you've got you know why our feet
would be different, why big feet would be different to
small feet? Right? You just think, well, maybe you've just
got longer bones, and I don't know.

Speaker 3 (00:36):
So this is a great study. So it's literally about
whether or not big human feet are just bigger versions
of small human feet. And as a person who is
married to a husband who has size sixteen feet, okay,
we had to design a special shoe wreck just to
hold his shoes. So I think about big feet all
the time because I'm like, oh, my kids are just
gonna be the same, aren't They'm going to have this
constant import from America type shoe house. And so I

(01:00):
looked at this study. It's published in the Royal Society
open Source. It's oversource. You can go and read it,
and it's really cute and what they did and they said, hey,
humans who have big feet are the same as humans
who have small feet, and did they form in the
same way? And so what they did is they took
different ages of people, different sizes of feet, and they
scan them with air CT scan I. So they did

(01:22):
really in depth three D CT scans to get every
slice of the bones of a foot, and they looked
at it in a computer model. And so they were
going to figure out basically, do the feet increase in
size proportionally? So do all the bones increase in size?
We call it m isometrically, So does everything go proportionally
or do different bones growm at different weights for different reasons.

(01:46):
And I think everybody in life is just assumeedful. Of course,
they're just all in proportion, just whatever else. And what's
important is shoe manufacturers assume this because they don't go,
you have a certain size of foot, therefore your foot
is different, your bones are different, therefore will make you
a different shit. Here's the thing. They're different. They are
not the same. So if you have big feet and

(02:07):
you're constantly getting like an ache in your ankle or
something just fromily because shoes are not designed for you.
So here's what they found. They looked at two very
specific bones, the tailus, which connects the foot to your
leg it's sort of around your ankle, and the calcanous,
which is your heel bone. And what they found is
that the tailus forms totally isometrically. Yes it's totally in proportion, great,

(02:30):
but your calcanous is very very differently and it does
not form proportionally. And so what they found is, first
of all, as your foot gets bigger, if you are
due to have bigger feet, your heel bone, this heel
bone also gets taller, wider, but shorter in length proportionally
than those people have smaller feet. And what they found

(02:54):
it was really interesting and sort of explains why this
is happening, is the joint surface, so the surface is
where it starts to contact. The other bones grow at
a much faster rate, suggesting that larger feet need a
larger contact area because the larger the contact area, you
reduce the overall pressure, so you're taking the pressure off
the bone. It's the reason why if you're in stilettos,

(03:16):
you put a high pressure on this just having a
wide foot, it's more comfortable. So those joints are the
ones that are growing faster because they're obviously going, hey,
we've got a bigger load. Because typically with bigger feet,
you're a bigger person than then for you've got more
mass coming down that grows first, and then everything else
captures up to support that joint. So if you have
bigger feet, you tend to be a bigger person, you

(03:37):
tend to put a bigger load on your joints. Your
body knows this, and it grows your feet to help
take away that joint pain. So if you do have
big feet and you're like, hey, my shoes don't seem
to be supporting me, they're probably not. They're bought for
regular sized people. And so I thought that was a
cute study, and I did. I thought we knew everything
about humans, you know, we're sort of like we've been

(03:58):
the scientist has been doing stuff for a while. But
feet are a lot more complicated than we give them
credit for, aren't they. I mean, there's so many little
bones and they're very common. It's a very complex part
of our body. And it's why this study only looked
at two of the sort of bigger bones, because it
was like, oh, we could do this all day.

Speaker 2 (04:13):
We could be here for decades.

Speaker 3 (04:15):
But the next time you look at somebody who with
big feet, just go hey, your feet are weird. They're
not the same as mine.

Speaker 2 (04:19):
Doctor Michelle Dickinson, thank you so much for your time
this morning.

Speaker 1 (04:24):
For more from the Sunday Session with Francesca Rudkin, listen
live to News Talks it'd be from nine am Sunday,
or follow the podcast on iHeartRadio.