BBC 4 (their more eclectic channel) had a very interesting show last week about the human foot. Aside from the fact that they dissected (well, somewhat ) a foot, they also had a few segments on the wonders of the foot in general.
Catch it if you can.
The show was called Dissected: The Incredible Foot. It was a companion to another show in which they dissected a hand.
In this case, the format of the show is to slowly work their way through the foot, while, between each layer, giving us a vignette about something else interesting about how the foot works and what some scientists have found out about how we walk and run.
I’m going to combine all the dissection stuff, and then go on to talk about the other segments.
They start by cutting through the skin of the heel, which by the way, was incredibly thick. I doubt the person whose foot they used was a barefooter, so for many of us that skin will be even thicker.
That yellow stuff is the fat padding. Interestingly, when they talked about it, it’s really not like padding from a sponge (or the foam that’s in athletic shoes), they said it is really more like bubble wrap, to provide superior shock absorption.
Next they went down to the plantar fascia.
This is the structure that ties together the arch of the foot. As we know, it’s also the structure that gets weakened by wearing shoes, and then causes troubles because of that.
(By the way, I did get a bit queasy watching it. My mirror neurons were imagining what it would feel like if they were cutting into my own feet, and it was not pleasant.)
Next down they showed a lot of the muscles that are under the plantar fascia.
These are the muscles that work all of the toes except for the big toe. When you are walking barefoot in the cold, these are (at least some of) the muscles that get used to generate heat to help keep your feet warm. They really don’t get used much when you are wearing shoes, so no wonder shod people get cold feet so easily.
They then went further and showed the tendons that make all the toes work.
For the smaller toes, the tendons attach to the muscles we just saw. However, for the big toe, that large tendon goes all the way up into the lower leg, where there is a much larger muscle near the calf to really give it the power we use for walking.
Finally, in their dissection, they showed the Achilles tendon.
Of course, it is huge, and where we also generate most of our power when walking.
Their first side segment was about the mechanics of walking and running. For that they used motion markers attached to the body and pressure plates. Here is their subject hitting a pressure plate while walking.
On the pressure plates we are then show how the pressures transfer from the heel to the ball of the foot (and toes) on push-off.
Landing on the heel:
Push-off:
I occasionally hear barefooters talking about how we are not supposed to land on our heels even when walking. That may be so, but I doubt it. Native barefooters do it. The heels entire structure has been developed to handle landing on the heel. We’ll already seen the enormous fat pad cushioning in the heel. But also, the heel bone in humans is incredibly larger than it is in other primates (that don’t walk upright the way we do). Our heel really is the way it is in order to handle that impact. (That said, I do know some barefooters who, while walking, do land simultaneously on their heels and forefoot.) And then they show running.
Huh? They showed the walker barefooted, but for running put them in shoes? But do notice the heel strike of their shod runner.
They discuss the impacts while running, and the stresses on the heel.
The arrow not only shows the stress on the heel, but the way that stress works its way up through the entire body. According to them, when you walk, the stress on your heel is generally about twice your body weight, but when running, that goes up to three times.
But they showed us another running shot.
They showed the shod running to contrast it with barefoot running.
I’m a bit bothered by their runner, who landed with what I though an extreme forefoot landing. That’s guaranteed to give tarsal problems over the long haul.
But it at least showed how the forces were less, and distributed better over the joints.
Another of their segments was on comparative anatomy, looking at the feet of other tetrapods (though mainly mammals). Here’s a selection of animal feet.
One of the examples they looked at was an elephant foot.
Where his fist is the elephant has a huge fat pad (kind of like our heel pad . . . on steroids). It turns out that elephants kind of walk around on built-in high heels. Except, of course, their tarsal bones a sized appropriately for doing so (ours, of course, are not).
Among the other animals looked at (oh, by the way, that’s biologist George McGavin, the host of the show) was a zebra.
The structures that correspond to our foot are illustrated between his hands. His left hand is up near what would be in us humans the heel bone. (By the way, this is really strong evidence for evolution, that the same structures are used over and over again, based on the initial structure of a remote ancestor, and then modified by genes during development into specialized shapes). The long bones between his hands are the tarsals, etc., that correspond to our third finger. (The other bones start to develop but are suppressed during development.)
They also have another segment featuring artist Tom Yendell, who was born without arms because his mother took thalidomide. He shows just how much dexterity you can get out of feet.
They also have George McGavin try it himself. He manages to grasp the pen, but cannot do much more.
Our feet cannot work for us, and that regard, as well as hands simply because the structures and joints only allow certain movements (for instance, the joints simply don’t allow an opposable big toe). However, if you try using your feet to draw, a lot of that is that you simply have not developed the neurons to give you the fine tuning. It feels awkward, so you stop trying.
It’s really rather like trying to use your opposite hand. I myself am fairly ambidextrous, but that’s mainly because I’ve worked on using my non-dominant hand so that over time it feels less awkward and I’ve developed the neurons to support that. In Tom Yendell’s case, he really had no choice, so he’s lost that awkwardness and shows us just how much feet can really do.
They also had a segment comparing our feet to those of orangutans. This segment I have a few doubts about. First they showed how orangs walk, on the sides of their feet.
Orangutans are mainly arboreal and don’t have much cause to actually walk, so their feet really don’t have walking adaptations.
But on the pressure pad, when they do walk, the rear pressure on their foot comes from a mid-tarsal bone.
In the show, they then demonstrated that a fair number of people also show a bit of mid-tarsal pressure while walking:
They interpreted this as meaning that we still retain some of the flexibility in our feet that orangutans have. Well, from my point of view, my first question is: how much of that is just from people walking a bit on the sides of their feet? Also, couldn’t it just be that that bone, in some people, sticks out more and thus can show up in a pressure chart? I have my doubts. It also bothered me that they’ve only looked at this in the terminally shod. Maybe it’s a sign of the weakness of shod feet and doesn’t show up at all in those who go barefoot all the time and have strong feet because of it.
There was one more segment that discussed the importance of proprioception, and the various things that can screw it up. This is one of the devices they use to do that.
They also screwed up his proprioception by having him walk on an elevated beam (in that case the fear of the height can tense one’s muscles and screw up the proprioception, which then becomes a feedback loop increasing our fear because our proprioception is screwed up and tensing our muscles even more).
But what they didn’t show (and I wish they would have) is how much shoes can screw up our proprioception and have that echo all through our bodies.
Here’s their final summation:
So even standing still, the muscles in our foot and calf are making constant and minute changes, just to keep us upright. And as they do this, those muscles provide our brain with essential information to help us balance.
Our feet really are remarkable. They’re sensitive enough to gather information about the world around us, and yet strong enough to bear all that weight pressing down on them. And yet we’re hardly even aware of the complex interactions that go on between our feet and our brain, that allow us to form the everyday act of walking.
All in all, it was a very interesting program. Again, it is here.
[It appears it is limited to viewers in the U.K.. If you are elsewhere and want to see it, I suggest that you look for an anonymizer (google it) that will let you claim you are in the U.K.. In addition to websites, many browsers have add-ons that will allow you to do such anonymization and location-spoofing fairly easily.]
Wow, Tom Yendell has some really terrible looking feet.
If you want to watch BBC programs overseas there are a couple of Firefox extensions that might do it.
Well, that certainly appears as though it would be painful for the subject. I about lost my lunch. I need to add this blog to the list of websites that I do not look at while eating now.
Maybe I wasn’t clear. The subject was dead. That was a cadaver!