updated 6/26/04
What Hurts You
The strange science of pain perception
by Paul Ingraham, Vancouver, Canada MOREclose
Credentials and qualifications
I am a writer and retired Registered Massage Therapist (unusually well-trained for a massage therapist, a 3000-hour program). I’m almost done with a Bachelor of Health Sciences degree. I am a peer reviewer for The Natural Standard, and a copyeditor for Science-Based Medicine. My most important qualification is more than a decade of workaholic post-graduate study, clinical experience, and constant conversations with readers from around the world, including many experts who have provided countless suggestions and criticisms.
For more information, see: Who Am I to Say? More information about my qualifications, credentials and professional experiences for my readers and customers.
Credentials and qualifications
I am a writer and retired Registered Massage Therapist (unusually well-trained for a massage therapist, a 3000-hour program). I’m almost done with a Bachelor of Health Sciences degree. I am a peer reviewer for The Natural Standard, and a copyeditor for Science-Based Medicine. My most important qualification is more than a decade of workaholic post-graduate study, clinical experience, and constant conversations with readers from around the world, including many experts who have provided countless suggestions and criticisms.
For more information, see: Who Am I to Say? More information about my qualifications, credentials and professional experiences for my readers and customers.
Articles in the Biological Literacy series are fun explorations of how the human body works. See below for a complete listing of articles in the series.
People often ask me, “Why does that hurt?” It’s not an easy question to answer. Best to start at the beginning …
Usually, the sensation of pain probably originates in nerve endings called “nociceptors” which doesn’t actually tell us much. Some nerve endings produce the sensation of pain, and we give them a nice Latin name. But we don’t know enough about what stimulates nociceptors, how many types there are or what the differences are, or what the brain does with the information they deliver. In fact, the brain may often generate the sensation of pain as well, which complicates everything quite a lot.
One thing that seems certain is that the pain of injury and tissue damage is stimulated by the release of molecules that are normally on the inside of cells. Such molecules floating free obviously means trouble, so the nerves respond by generating nerve impulses. But that’s only the simplest possible example. Everything gets stranger after that.
Consider a toe-stub. In a typical stub, there is no tissue damage to speak of. Yet toe stubs can be excruciating! This kind of pain is produced by “redlining” ordinary sensations. Any sensation in excess — sudden, strong pressure in this case — gets interpreted as pain. Obviously, any situation that creates excessive sensation could be dangerous, so this kind of pain keeps us from being too rough with ourselves.
Three competing theories
What about muscle pain the day after a workout? That kind of pain is called delayed-onset muscle soreness. There are several competing theories1 to explain it. The most popular is that a hard workout causes microscopic tissue damage (“microtrauma”), which certainly sounds sensible. Unfortunately, it hasn’t been verified and the experts argue about it.
Another unexplained kind of pain is the most common type of pain in the world: the pain of “knots” in your muscles. Stiff necks and throbbing backs. This is the kind of pain that I try to help people with every day. Again, the only explanations are theories.2 For instance: one theory is that tight muscles strangle their own blood supply, restricting the amount of metabolic waste that can be flushed away. The very toxic tissue fluid then aggravates the nociceptors. Maybe. Or maybe we’ve got it all wrong.
There are so many more mysteries in the study of pain that I can only list them here: cramps, nausea, migraines, radiating pain from organs, trigger point referral patterns with no anatomical correlates, amputee ghost pain, the extreme pain sensitivities of people with fibromyalgia — all of these are poorly understood pain phenomena.
Pain tolerance
One mystery fascinates me more than the others: the variability of pain tolerance. Some people are much tougher than others. At one end of the extreme, I have clients who seem nearly immune to pressure and pain. At the other extreme, a few clients cannot tolerate more than a feather-light touch, so sensitive that I have sometimes wondered how such people can wear clothing without pain. Many of these people are superficially healthy … yet you can barely touch them.
Some people are much tougher than others.
The sensitivity also seems to translate into real fragility. Not only do these people feel more pain, they are damaged more easily. Even modest pressure could cause bruising and loss of function. To do the same to a tougher client, I would have to use a baseball bat. Why? Can there really be that much of a difference in the tissues? Why would one person’s muscle be fit to put in a vice grip with no consequences, and another be hobbled for a week by massage no stronger than a firm handshake? I honestly don’t know. But there seems to be some implication that the relationship between tissue and pain is reciprocal: that the sensation of pain changes tissue, just as the condition of tissue changes sensation.
That’s an introduction to some of the strange science of pain. I regret that there are not more solid facts to report! Stay tuned. Perhaps there will be more to tell in another fifty years.
The Biological Literacy Series
- Dance of the Sarcomeres — A mental picture of muscle knot physiology explains four familiar features of muscle pain
- The ‘Use It Or Lose It’ Principle — The importance of stimulation and movement in healing
- Natural Imperfection — Evolution doesn’t care if you have back pain … just as long as you can breed
- Oh, a flow-induced system of mechanotransduction! Of course! — A century-old mystery of bone biology was solved just a little while ago
- Eccentric Contraction — A peculiar phenomenon in muscle physiology
- Stiffness, tightness and limited range of motion are not always the same thing — An interesting little thing to understand about your body
- We Are Full of Critters — The human body is a colony of ten trillion co-operating cells
- How Many Muscles? — A (slightly tongue-in-cheek) tally of the body’s many muscles
- The Sixth Sense — Proprioception, the vital but mysterious sensation of position and movement
- Ugly Bags of Mostly Water — The chemical composition of human biology
- An Introduction to Biological Literacy — Why you need to know more about your body
- What Hurts You — The strange science of pain perception
Notes
- See “Persistent myalgia following whiplash”. Return to text.
- See Save Yourself from Trigger Points & Myofascial Pain Syndrome!. Return to text.