Proprioception: updated thoughts

How do you sense where you are located in space? Not just, “my arm is by the side of my body,” but “my arm is within grasping distance of the object located to my right.” If you were to close your eyes and try and touch right index finger to your left nostril, could you? What about your right foot to your left knee? If you are standing, that’s probably a little bit harder, but why? Is it “just” that your balance is off? Why is your balance off?

Proprioception, or our awareness of where our body is located in space, is often considered our sixth sense, arguably as important as our other five senses (touch, sight, smell, hearing, and taste). It’s our innate knowledge of our physical self, and it reduces the separation between the mind and the body. Just like a sommelier has a heightened sense of taste and smell compared to, say, me, the person who spends time practicing physical tasks moves in a way that is more coordinated, balanced, and integrated than his less movement practiced cousin.

Proprioception is determined not only by our level of physical activity, but also by things like previous physical trauma and genetics. Our ligaments, the cartilaginous tissue that connects bones other bones, are filled with mechanoreceptors that determine joint position. Joint sprains/injuries and genetic predisposition to laxity can affect proprioception- where you think you are located in space doesn’t always match where you are actually located in space.

Habituated patterns can also affect proprioception. Take the person who habitually stands at attention, with his shoulders thrown back, his chest puffed out, and hips thrust forward. His perception is he is standing up straight when, in actuality, he is standing arched back. When asked to soften the ribs so they move down, broaden his shoulder blades so his arms hang loosely by his sides, and stand in the middle of his feet instead of his heels he feels like he is slouching. If you were to take a picture of him from the sides, he would look more straight in the second scenario, but this contradicts the internal image of he has of himself. 

Patterns:

Proprioception isn’t just a matter of how we perceive our resting position. It is also our sense of how we maneuver through space. It enables us to step off curbs without looking down and allows us to reach back for the water glass and “just know” where it is. We interact with the world largely through this relationship between how our body moves and where things around us are located. Our response to the world is predicated on our ability to just know how to move.

Pretend you have a job that requires a lot of screen time and your favorite form of physical activity is lifting weights. You like the traditional lifts, so you do things like bench press and rows, lat pull downs and shoulder presses. Your life doesn’t require your arm to move behind you very much, if at all.

Time passes, and it’s been months since you have reached your arm behind you, let alone placed any body weight on your arm when it’s in that position. Is it any surprise that when, on whim, you decide to teach yourself the Turkish Get-up, it goes a bit disastrously and your shoulders and arms are sore for several days?

There are a number of reasons for this (the muscles are de-conditioned at that joint angle, it’s a move you have never done before), but I think it’s worthwhile to remember that if you haven’t recognized that part of yourself for months, or even years, it shouldn’t be a surprise that the neuromuscular system overcompensates in the form of excess sensation. 

Stretch:

The same thing happens when a person first approaches a joint angle that hasn’t been used in a while. The sensation of stretch is high. Again, multiple factors cause this, but if you stretch, walk away to perform another exercise, and return to the same stretch, the sensation will be less. Why?

The mechanoreceptors that determine stretch are a little less loud the second time around because the “new” joint angle is no longer novel- it’s not scary or threatening, and the memory of the position is still fresh. Your brain is learning to access a part of your body that was previously, in a sense, unrecognizable. Repeated exposure to the new joint angle will eventually quiet the sensation of stretch, partially because there has been an increase in proprioception. The outline of your internal view of what you look like begins to look a little more complete.

Scientists have identified a gene specifically related to the ability to sense force, a key aspect of proprioception, named PIEZO2. Examinations of two subjects born with variants in the PIEZO2 that rendered it essentially ineffective found both subjects had difficulty reaching and had shallow breathing as babies. They could not feel light touch or detect vibration against the skin, and they were unable to perform touching tasks with their eyes closed. Their movements were bigger and less coordinated than their fully PIEZO2 functioning counterparts. Though they were still able to feel pain and had normal strength and cognitive function, their ability to maneuver through the world in a way that felt safe and secure was diminished.

Have you ever climbed up on something just a little too high, only to look down and feel a wave of insecurity (and maybe a touch of nausea) as you realize you aren’t sure how you are going to get down? You don’t trust your body to know how to scale the tree/counter/rock that you just climbed and the fear you are experiencing is almost paralyzing. 

Short of channeling your inner Alex Hannold, what do you do? You probably suck it up, cross your fingers and hope that no imminent harm is done as you figure it out.

Once you are on solid ground with no expansive drop beneath you, your heart rate will be elevated, your breathing rate a little bit quickened, and an alternating sense of tension and relief will wash over you. People living without PIEZO2 feel this way regularly while performing tasks many of us take for granted. A sense of safety is necessary to perform a movement skill in a coordinated way; lack of safety results in both over-efforting and a heightened focus of the other senses as you work to maintain self preservation.

Force:

Perhaps one of the most interesting aspects of proprioception is the innate awareness of how much force is needed for a particular task. Someone whose proprioception is finely tuned knows how to dial force up and down to match task demands. 

Whenever you are exposed to a movement skill for the first time, or when you are asked to do a skill you’ve done many times in a new way, the level of force used will be high. Just like when you are asked to place your limb at a joint position that is novel and the sensation of stretch is high, new movements require the neuromuscular system to figure out how much effort is necessary. Motor unit recruitment (which allows for the appropriate contraction to occur), appears to be modulated by the information received from proprioception. 

Let’s say you are being instructed to take your right knee behind you without arching your back. You are struggling, since this is the first time you can remember doing the movement this way, and the instructor has you come into a 1/2 kneeling position with the right knee behind you so you can “feel” the position a little bit better. While there, he has you perform some pelvis tilts to feel the pelvis move around the femur. At some point, he stops you with your pelvis in a very slight posterior pelvis tilt and asks you to feel like your left hip bone is moving back while your right hip bone moves forward. He stops you again in what feels to you like your right hip bone is far past your left hip bone, but when you look down you see they are even, and asks you to breathe. As you breathe, you feel your right glute and abdominals in a way that is both intense and completely foreign. When you are told to relax, you happily come out of it, surprised that such a simple looking movement could result in the sensation of so much work. What just happened?

You were asked to perform a familiar movement in a new way. The new way resulted in lots of motor units being recruited, while the nervous system figured out what was required. If you were to do the same exact position a second time, the sensation of effort would be a little bit less- your neuromuscular system would begin to figure out exactly how much effort was needed to be in that position.

With repeated exposure, the position would still feel like work, but not as much work as the very first time you did it. You could turn the volume knob up if you wanted and make the sensation of work higher, or, as your strength increased, you could turn the knob down and make the movement feel easy, especially if given the right cues. You begin to regulate the effort to meet the demands of the entire goal- what are you trying to do? How much force is needed to do it?

Proprioception is a critical aspect to moving well. Take the time to feel where your body is in space and how it moves through space. How do you interact with the environment? How much force are you using to perform a specific skill? Is it appropriate for the demands of the task? If not, why not? Can you adapt to different surfaces, different grips, different textures? Body awareness improves not just through moving a variety of ways, but in a variety of environments. Practice adaptability and variability to improve resilience and, ultimately, strength.

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