As barefooters, I think we’re all pretty much aware of the importance of proprioception, the awareness of our body position which comes from our sense of touch and our perceived motions. It is sometimes called our “sixth sense”.
Unsurprisingly, shoes limit our proprioceptive sense and that can lead to falls and other difficulties.
And you might just bite off your foot.
Dr. Steven Robbins of McGill University is one of the pioneers in studying how footwear has affected proprioception. In Proprioception and Stability: Foot Position Awareness as a Function of Age and Footwear, published in Age and Aging in 1995, he and fellow researchers found (from the abstract):
We found significant differences between the two groups in terms of estimates and the effect of footwear. Psychophysical functions for estimate of slope were 0.95 for the young when barefoot and 0.71 when shod compared with 0.80 and 0.81 respectively for the older men.
We conclude that sensitivity to foot position declines with age, mainly owing to loss of plantar tactile sensitivity. Footwear impairs foot position awareness in both young and old. Loss of foot position awareness may contribute to the frequency of falls in later life.
Dr. Daniel Lieberman, as we all know, is one of those who has taken up such research. Here’s what he says about proprioception in What We Can Learn About Running from Barefoot Running: An Evolutionary Medical Perspective in the April 2012 issue of Exercise & Sport Sciences Reviews.
First, shoes limit proprioception. Sensory feedback from the plantar surface of the foot evolved in early tetrapods as an adaptation for sensing characteristics of the ground including hardness, roughness, unevenness, and the presence of potentially dangerous objects such as sharp rocks. Plantar proprioception activates reflexes and helps the central nervous system make decisions that help increase stability and avoid injury. If so, then the way in which people run when barefoot likely is to reflect the effect of ancient evolved proprioceptive adaptations to maintain stability, to avoid painful impacts, and to modulate leg stiffness. In turn, these feedback mechanisms, which are curtailed in a shoe, may help avoid some traumatic and repetitive injuries
He also notes that a lot more research needs to be done to fully understand the impact of footwear on, well, impact when running or walking.
But what prompted this blog entry was a story I read in which the lack of proprioception really did make a huge difference. Yes, I’m looking at it a bit whimsically, but still . . .
The story is Here’s What Happens To Snakes In Microgravity.
Researchers seem to like exposing animals to microgravity (µ-G) to see how they’ll react. They’ll take them up on the vomit comet (a special airplane) to do a parabolic loop and get some extended time in µ-G. Snakes, of course, touch the ground with their whole bodies, and it turns out that they really do get their sense of “self” (whatever that means to a snake) from their proprioception.
In a 1993 paper in Zoological Science, The behavioral reactions of a snake and a turtle to abrupt decreases in gravity, Wassersug and Izumi-Kuratani report on a striped rat snake that, after losing that proprioception, actually attacked itself because it could no longer tell that it was part of itself.
As they put it,
The fact that the snake actually struck at itself suggests that the animal suffered loss of proprioceptive clues about body position in µ-G.
In a later 2005 paper, Wassersug did not observe the snakes striking themselves, but they did go into a self-embrace, trying to knot themselves up. Here, the researchers say
Although this behavior seems profoundly different than an aggressive display directed towards a snake’s own body, both the strike seenin E. quadrivirgata and the self-embrace seen in E. obsoleta and T. sauritus share the basic common feature of loss of proprioception. Both indicate that in the absence of gravity, snakes have difficulty distinguishing self from non-self.
I do know that when I am forced to wear shoes, I’m usually about ready to gnaw my feet off from lack of proprioception. 🙂
But the lack of proprioception can also have a profound, and deadly effect. There is a show on the Smithsonian Channel called “Air Disasters” which is quite fascinating. They re-enact various airplane crashes and look at the efforts to find out what went wrong. One of their latest was Hockey Team Tragedy, about the loss of a major Russian hockey team upon take-off.
What happened was that the pilots (who had pulled rank to be the ones for this particularly prestigious flight) were somewhat unfamiliar with the YAK-42 airplane they were flying, being more recently trained in the YAK-40.
And there was a difference in the brake pedals between the two planes.
In the YAK-40, you rested your heel in the heel cup. In the YAK-42, your heel rested on the ground.
It turned out that the plane, while trying to take off, had its brakes partially on. The braking force caused the nose to dip (it also meant that they were having to increase engine thrust too, obviously). But with the nose dipped, their ailerons were not set at the right angle to get off the ground. (Correction: as per the comments, and upon rechecking the episode, it was the stabilizers that were not at the correct angle with the nose dipped due to the brakes.) So the pilots increased the angle. But as soon as the plane left the ground, the brakes were no longer keeping the nose down, so the nose leapt into the air, which meant that the plane’s angle was too steep and it went into a stall and crashed.
How could it be that the brake pedal was depressed? If the heel is supposed to be on the ground, but is instead resting fully on the pedal, it is really easy to be applying the brake without realizing it.
I think anybody who has ever driven barefoot knows how that, under those conditions, the pilot’s shoes would have inhibited any feedback about pressure being applied to the brake pedal. The pilot had a lack of proprioception as to exactly what his feet were doing.
In my opinion, this is a situation that would not have happened if the pilots had been flying barefoot. They would have been able to feel that they were applying braking force.
It’s worse than that. One of the pilots suffered from polyneuropathy, which causes a loss of feeling in the extremities. See Yak-42 Russian Plane Crash: Pilot Error Blamed In Crash That Killed Hockey Team. While they don’t know which pilot was applying the brakes, I’d say it was a good chance that it was the one with the neuropathy. Not only were his shoes preventing him from feeling what he was doing, the neuropathy would have exacerbated that.
Going barefoot can make up for some of the problems with neuropathy, and I experience that myself. My spine is busy deteriorating and I am getting numbness on my left side. Putting on shoes or anything with an artificial sole really affects what I feel when I walk and causes me problems. When suffering from neuropathy, putting any extra barrier between your sense of touch and what you are doing makes no sense at all.
But that is exactly what that pilot was doing. Because, of course, if you are a pilot you really, really need to dress for the part, and fancy dress shoes will inspire confidence in the people you are flying. That is what our culture has dictated, even when it may not actually be true.
Yet we would not have pilots wear really smart-looking gloves that inhibited their pushing the right buttons.
In the end, proprioception is one of those things that very few people realize the importance of. Heck, I suspect most people have never even heard of the word.
But it really is a determiner of self and non-self, and life and death.