Your Back Hurts, and I Look at Your Foot

"My back is what hurts — why are you looking at my foot?"

It is something I hear often in the consulting room. The back is what hurts, and here I am holding the ankle and moving it about, so it is fair to find it odd.

When I explain, most people are satisfied. It is because the way the body holds a posture is closer to a calculation than you would think.

The body works out its own posture through sensation

Even standing with our eyes closed, we know that we are standing. We know roughly where our arm is without looking at it.

Inside muscle and tendon and joint there are sense organs that measure their own length and tension and angle. The information that comes up from them is called proprioception. Added to this is pressure information from the skin of the sole pressing on the floor.

The brain gathers this information, calculates what shape the body is in right now, and decides which muscles to use and how much to match that calculation. It is work that runs without stopping while we are unaware of it.

When the information goes blurry, the calculation wavers

This can be confirmed by experiment.

If you have someone stand on soft foam, the pressure information the sole receives is smeared. Then the body's sway grows immediately. The muscles have not weakened and the joints have not been damaged, yet simply from the quality of the information dropping, balance gets worse.

When you are standing, the sole of the foot is the surface where the body meets the floor, so the share of the information that comes up from here is large.

Once you have hurt an ankle, that sense stays dulled

There are many people who have turned an ankle. Most remember it as having hurt for a few days and then stopped.

But in material gathering together a number of studies, in people whose ankles are repeatedly unstable, the position sense of that ankle itself really was dulled. Even after the swelling had gone down and walking was no longer a problem, the sense side had not recovered along with it.

And after an ankle injury, the way the muscles above it are used changes too. Doing the same movement, the order and the degree to which they are recruited are not what they were before. The body reassembles its posture with the sense out of true.

The body is connected like a net

The membrane wrapping muscle is not something each muscle has separately — it runs on through the whole body. There is a line that runs from the sole of the foot up the back of the calf, across the back, and on to the head.

Pull one corner of a net and the opposite side moves. So tension that starts in one place comes to be felt in a distant place. If you draw this only with bones and levers, it does not explain well. Bone is closer to a pillar holding out inside the net, and what actually sets the shape is the tension strung between them.

The frame for seeing the body this way is called tensegrity — a structure that holds its form through a balance of tension and compression. I use it not as a settled map but as a picture that lets you see. Even so, there is a great deal in the consulting room that this picture does explain.

So what I do

I feel the place that hurts first, and after that I look at why that place ended up taking on the work.

I have the person stand on one foot, I look at which direction the ankle sways easily in, and I look at where on the sole touches down first. And then I work on the side where the information is out of true. There are cases where the painful spot keeps being released and it comes back before long, and then it is usually because the material for the calculation is unchanged.

This story continues from If treating the painful spot doesn't cure it. If that piece dealt with where the force moves to, this one is a story about what the body looks at in deciding that.

The side that holds posture from the middle of the trunk I have written down separately. (What You Can Tell by Laying a Hand on the Belly) If the foot is the side sending information up, the belly is the side that holds the body with that information.

When to see a doctor first

If the leg goes weak, if there is a distinct patch where sensation has dulled, if bowel or bladder control has changed, if pain wakes you at night, or if you cannot put weight on it since an injury — before this story, examination and testing come first.

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Sources

• An analysis gathering together a number of studies confirming that in people whose ankles are repeatedly unstable the position sense of that ankle itself is dulled — Journal of Sport and Health Science, 2020
• A study measuring that blurring the pressure information the sole receives immediately increases the body's sway — Frontiers in Human Neuroscience, 2016

Written by Dr. Heo Ji-young (Ph.D. in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)