The physiology of sensation when you’re being pressed and moved around
Most people are amazed by the amount of sensation produced by pressure on their muscles. “I can feel that all the way down in my toes!” That’s a common sentiment expressed on a massage table — usually muffled by the face rest. How does that work? What’s going on?
Muscle is a sensory organ
Muscle tissue is about half of the average person by weight (most of us try not to think about the other half), and it is chock full of nerve endings. Also, muscle tissue is thoroughly mixed with connective tissues like tendons and ligaments and intricate wrappings called “fascia”1 — and connective tissue is also full of nerve endings.
All those nerve endings produce sensation — a lot of sensation. In fact, they produce more sensation than all the other senses combined.2
Muscle is a sensory organ.3 A big sensory organ, much more massive even than your skin. How your muscles feel is how your body feels! You are your muscles.
The sixth sense
Those nerve endings detect pressure, movement, stretch, velocity of muscle contraction, and much more. And some of it’s uncomfortable, too: like fatigue and pain during exercise, caused by nerves that pick up cocktails of metabolites.4 All together, about half of all sensory information sent to the spinal cord and brain comes from these nerves.
We couldn’t even stand up without this sensory information. Without it, you wouldn’t even be able to locate your body: you wouldn’t be able to feel it In fact, there is a rare neurological condition in which people lose their proprioception, and the consequence is a devastating and surreal disembodiment.5
Yet hardly anyone knows that it is a sense. Most people have never even heard the name for it.
Physiologists call it “proprioception.” Proprioception is the real “sixth sense” — not clairvoyance, but the very real and physical sense of effort, position and movement.
Strangely, though, most people aren’t aware of how their muscles feel until they start to hurt. If proprioception produces so much information, why aren’t we aware of it?
Raising sensory awareness
We aren’t normally aware of our proprioception because it’s always on, and there’s always a lot of it. It’s like trying to describe daylight in a world where the sun never sets or even goes behind a cloud. Proprioception is just there.
We can turn the other senses off, or easily turn the volume up or down. We can close our eyes and plug our noses. We can touch more or we can touch less. Taste doesn’t have much to tell us without food in our mouths. But proprioception is always on. No matter what position you are in, you are still in a position.
If we could switch proprioception off, it would suddenly be obvious what we were missing. But normal proprioception is a sense without a lot of contrasts. Until you get on a massage table.
Massage therapy produces a lot of unexpected and unusual proprioceptive data. You can’t turn your muscle sensations off … but you can give them extra stimuli, and new and interesting stimuli. And they love it!
Surprise! Novel sensory input
Your nervous system craves data. It’s like a drug.
Baby mammals, including us, literally die or grow up brain-damaged without lots of sensory stimulation.6 Their nervous systems need input in order to know how to grow. We don’t just learn about the world through sensation — we learn about our selves. The developing organism can’t define self unless it can feel other.
As adults, we no longer need that input to survive — but we still need it to thrive. We still want to entertain our senses. We like to touch, to be dazzled by sights and sounds, to stop and smell the roses and taste great food.
Touch is neglected in our culture, of course, and we tend to neglect proprioception completely. People engage in physical activity, of course, which is proprioceptively stimulating — anything from dancing to skiing — but they don’t do it for the proprioception, and the sensations are pretty much what you’re brain expected.
It’s friendly sensory surprises the nervous system really likes. You don’t know what a delicious meal is going to taste like until you put it in your mouth, but your body knows exactly what your next dance move is before you do it. The only way you can easily surprise your proprioception is with massage: with passive stimulation of your proprioceptive sense.
And we are surprised not just by the quality of sensations that massage produces, but by the quantity — as much sensation as all the other senses combined. What a rush!
And that’s why we tingle from head to toe when we’re getting massaged.
About Paul Ingraham
I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.