By Bernie Clark
May 14, 2023
How is your proprioception doing these days? Try this common experiment: sit with eyes closed and touch the tip of your right forefinger to the tip of your nose. Then try the same thing with your left forefinger. Pretty easy, right? Unless you have been imbibing some mind-altering substances, you should have no problem. But, let’s increase the degree of difficulty a little bit. Sitting again with eyes closed and arms spread wide, touch the tips of both forefingers together out in front of you. Did you miss? Did you come close but not quite hit the mark? Did you nail it? If so, you are ready for the big test. Stand in Tree pose, with your eyes closed, on your tippy toes!1
Proprioception has been defined as “the neural process by which the body takes in sensory input from the surrounding environment and integrates that information to produce a motor response.”2 David Lesondak, in his book Fascia: What it is and Why it Matters, gives a more poetic definition: proprioception is Latin for “to grasp one’s self”. The neurologist Oliver Sacks said it is the “the unconscious sense that allows you to move normally.”3 Also termed kinesthesia, proprioception is the process which guides all of our movements. The process involves not only our muscles but also the nerves which activate the muscles and the nerves that sense where the body is in space and the relationship between all the various parts of the body. The nerves responsible for proprioception are called sensory nerves.
Proprioception is trainable. That is good news because poor proprioception is linked to body dysfunction and pain. “Proprioceptive training is any intervention aiming to improve proprioceptive function with the ultimate goal to enhance motor function and performance.”4 Try that second test, touching the tips of your forefingers together, with your eyes open. Easy! Do it a couple of times, then try with eyes closed. Was that better? You just trained your proprioception.
Sensory nerves in our fascia
Surprisingly, there are way more nerve endings in the fascia surrounding and embedded in our muscles than are in the muscles. Also surprising, the nerve bundles that connect our brains to our muscles contain three times more sensory fibers than motor fibers. This means the brain pays more attention to feedback from the muscles than giving directions to them. We need to know about where we are more than how or when to move. The sensory nerves in our fascia are called mechanoreceptions, because they react to mechanical stresses: pressure, stretch, compression, and vibration. There are somewhere around 250 million nerve endings in our fascia, which makes it the largest sensory organ in our body.5
Types of fascia mechanoreceptors
In his book, Lesondak describes five types of mechanoreceptors:
Muscle spindles: Found in the facia around the belly of the muscle (perimysium) arranged in parallel to the muscle fibers. They sense how much stress a muscle is undergoing and how fast that stress develops. If the stress is too much or too quick, they cause the muscle to contract more strongly.
Golgi receptors: found in deep fascia and in the myotendinous junctions (where tendon becomes the muscle’s embedded fascia). In the myotendinous junctions they are named Golgi tendon organs. In ligaments, they are named Golgi end organs. Only 10% of Golgi receptors are found in the tendon; the other 90% are in ligaments, joint capsules, muscle part of myotendinous junctions, and aponeurosis (spread out sheets of fascia). They are arranged in series with these tissues. If they sense a slow stretch in the fascia, they signal the nervous system to reduce muscle tone, which should reduce the stress in the fascia.
Pacini receptors: These egg-shaped receptors are found in the tendinous portions of the myotendinous junction, deep capsular layers of the joints, the epimysium wrapping the whole muscle, spinal ligaments and facet joints. They respond to sudden changes in pressure and vibrations. When activated they increase our proprioception and motor control. They are also found in our pancreas! This is one reason we feel deep pulsating bass music in our gut.
Ruffini receptors: found in our skin and superficial fascia, ligaments of peripheral joints, fascia encasing our nerves, and the fascial layer of joint capsules. They respond to vibration, pressure and shearing forces. This is heightened when sustained pressure is combine with shear. For example, in a long-held massage pressure or long marinating yin yoga posture they cause a global decrease in muscle tone. Chill dude! Relax. That’s Ruffini talking.
Interstitial receptors: These are the “free nerve endings”. They are the most abundant and mysterious mechanoreceptors in our fascia and are found everywhere. From the base of hairs, to the inside bone, and all places in between. They report on tension and changes in tension, pressure, temperature (hot and cold), acidity (ph) levels, chemicals that cause damage, etc.6 The interstitial receptors provide feedback to our autonomous nervous system which can then affect our breath, heart rate and blood flow. They can cause blood vessels to narrow (increase blood pressure) or widen (decrease blood pressure). More problematic, most of these free nerve endings are our pain receptors. Any problems with their improper activation may be a cause of chronic pain conditions.
Interstitial receptors can be multi-modal, which means they can sense multiple inputs, but they can only report on one type of input at a time. A free nerve ending that is jangling with pain can also sense pressure, but it has to choose which signal to pass on to the brain. If you bang your shin against a table, it hurts. That is the free nerve ending reporting on the damage to your tissue, but if you rub the shin, now the nerve ending starts to report on the pressure it is experiencing. While reporting on pressure, it cannot report on the pain. This is why we can rub or massage away some forms of pain.
Some areas have more mechanoreceptors than others. For example, the bands of fascia that often wrap our limbs close to a joint, called retinacula, have a surplus of Pacini, Ruffini and free nerve endings. Where we used to think that the role of a retinacula was to redirect forces and stabilize a joint, the newer understanding is that they are proprioceptors, sensing loads and the movement of the joints.
Poor Proprioception and Improving it
Lesondak reports that proprioception is impaired when the muscles are tired, and also under conditions of chronic pain. Robert Schleip has found that our fascia is the most pain prone tissue in our body, far more sensitive than our muscles. If this is so, then poor proprioception may be a cause of chronic pain. If that speculation is true, then improved proprioception should reduce pain. Some studies suggest this is true and clinicians have observed it anecdotally, but there is not enough evidence to really verify it. But in the laboratory of your own body, your yoga practice may demonstrate that improved coordinated movements reduce pain and discomfort. Schleip also reports that proprioceptive training has been shown to be effective in reducing the frequency of injuries in athletes.
Unfortunately, the studies are not definitive but they are suggestive. They vary in the length and duration of interventions and the type of interventions, which may explain why the findings are so variable.7 Often the interventions include balance work: standing on one leg, using a wobble board, or performing other challenging movements with eyes closed. Tai Chi, yoga and meditation have been studied and do show some improvement in proprioception for people with conditions like Parkinson’s, diabetes and knee ACL injuries as well as for older populations.
My own personal experience is that practicing yoga with eyes closed seems to help maintain my proprioception and balance. But the big test, standing on tippy toes with eyes closed in Tree pose, is still beyond me. Timber!
__________________________________
[1] T.K.V. Desikachar once said that Tree pose on tip toes with eyes closed is the hardest pose in yoga.
[2] Rivera MJ, Winkelmann ZK, Powden CJ, Games KE. Proprioceptive Training for the Prevention of Ankle Sprains: An Evidence-Based Review. J Athl Train. 2017 Nov;52(11):1065-1067. doi: 10.4085/1062-6050-52.11.16. Epub 2017 Nov 15. PMID: 29140127; PMCID: PMC5737043.
[3] Fascia: What it is and Why it Matters, 2nd ed., by David Lesondak, Handspring Publishing 2023, page 89.
[4] Winter L, Huang Q, Sertic JVL, Konczak J. The Effectiveness of Proprioceptive Training for Improving Motor Performance and Motor Dysfunction: A Systematic Review. Front Rehabil Sci. 2022 Apr 8;3:830166. doi: 10.3389/fresc.2022.830166. PMID: 36188962; PMCID: PMC9397687.
[5] Fascia: The Tensional Network of the Human Body, 2nd edition, Robert Schleip et. al., Elsevier 2022, pages 156-159.
[6] Etc. includes sensing hot, cold, hunger, thirst, itch, sensual touch – often termed interoception. Disorders in interoception are implicated in many psychosomatic disorders, depression and anxiety as well as eating disorders. They might include irritable bowel, fibromyalgia and chronic fatigue.
[7] Winter et. al. 2022.