The pain equation

Doctors and researchers have written a lot about pain. The International Association for the Study of Pain (IASP) defines it as:

An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage(1). 

After a long period of consultation, they’re considering changing it to:

An aversive sensory and emotional experience typically caused by, or resembling that caused by, actual or potential tissue injury (2). 

Spot the difference?

I’ve specialised in lower back pain for the best part of thirty years. And I’m constantly looking for ways of helping people in pain. You need to feel empowered so you can regain control over your pain and your life.

A single event brought me a flash of insight.

Insight

I was cycling to work early one morning along idyllic country roads. Suddenly my thoughts were interrupted by a sharp jab half-way down the front of my left thigh.

I looked down to see a wasp sitting on my cycle shorts. I’d been stung. And I had an opportunity to observe my own experience of pain. I still had forty minutes of cycling ahead of me, so I had plenty of time.

Ow, that’s sore. Never mind, I’ve been stung before. It’s not a big deal. (Pain level low).

Watch out, you crazy badger. Nearly ran you over there. (Pain level zero).

How’s my thigh? It’s still sore. I wonder if it’s swelling. Yep, swelling already. (Pain level medium.)

Busy junction coming up. Better pay attention to the traffic. He’s coming slowly. I can get out in front of him. I need some serious effort to get up this hill. (Pain level zero.)

The road’s quieter now. Wonder how my thigh’s doing? Still sore, though not too bad. No worse than ten minutes ago. I wonder if I’ll have an anaphylactic shock response. I’ve never had one before due to a wasp sting but my lip and tongue swelled up a few years ago when I ate that hazelnut. It’s a good thing I’m not far from the hospital. (Pain level highest yet.)

Busy traffic. That guy cut me up on purpose. What an XXX. (Pain level zero.)

My pain levels had varied between 0 and 5 on a scale of 0-10, averaging 2-3. And as soon as I got into work I made notes on my observations. These led to my equation for pain.

Equation

P = (N – MWP) + (NO – PO) + (ATBP) + (PVOP)

Let’s break this down.

P represents the level of pain you experience at any given moment

N means nociception

When something bad happens to your body, nociceptors detect noxious events such as physical trauma, extremes of temperature, or chemical changes (like inflammation). The local nociceptors fire and send a message to the next neuron (nerve cell).

Nociception is a variable in the equation for pain. The more damage or inflammation, the more nociceptive input you’re likely to have.

But it’s not quite that simple.

The wasp released a toxin into my thigh. This caused nociceptors to fire and inflammation to build up, along with more nociceptive activity. Although the inflammation remained fairly constant over the next two days, the pain didn’t – it varied.

MWP means movement without pain

Why do you rub something that hurts? Why do people jump around when they hit their thumb with a hammer? Because the more movement you can do that doesn’t cause pain, the less pain you’re likely to feel. Ronald Melzack and Patrick  Wall first described this in 1965 as the Gate Control Theory (3).

When you move around, you stimulate sensory neurons called mechanoreceptors. They detect movement and pressure within tissues. When they fire, they block nociceptor messages.  So the next neurons in the pain pathways in your spinal cord/brain don’t fire.

Brilliant, isn’t it? TENS (transcutaneous electrical nerve stimulation) uses this system to reduce pain. (TENS machines are often used by  women in labour to reduce pain.)

If you move around enough, your brain releases chemicals that suppress your pain system. For example, when you exercise. (There’s a debate about whether endorphins or endocannabinoids are responsible for this.) Movement can reduce the nociceptive input into the spinal cord. And it can suppress it via these naturally occurring chemicals.

When I was busy with other activities, I didn’t feel any pain. 

NO means negative outlook

If you are prone to depression or anxiety or feel stressed, you’re likely to experience more pain. The pain pathways pass through the parts of your brain responsible for emotions and motivation. And your deepest motivating emotion is fear.

Worrying is an expression of fear. The more worry/fear you have, the more active this system is. And that augments your pain-pathway activity. Your pain system and your emotional centres share neurons, so if fear is “firing”, pain is more likely to fire too.

I like to describe stress as fear. For example, fear you won’t get paid this month. Fear you’ll lose your job and you won’t be able to pay your mortgage. Fear you might get sick or perform badly at work.

You may not be facing those fears consciously. But if you look inside yourself, they’ll be there.

When I was stressed, I felt more pain. It was no coincidence. When I thought about the possibility of anaphylaxis, my pain levels were at their highest.

PO means positive outlook

Fortunately, a positive outlook can reduce pain. Your brain releases chemicals when you’re enjoying yourself or connecting with other people in a positive way. And these chemicals reduce your pain.

So if you’re feeling pain, do something you enjoy. Spend time with people you find uplifting, especially if you can move at the same time. Team sports, and dancing with a partner you really like reduces pain levels dramatically, combining MWP and PO.

When I remembered that I haven’t had anaphylaxis and I’m generally pretty lucky, my pain decreased immediately.

ATBP means attention to body part

The more you think about it, the more it will hurt. Attention to pain has a greater impact than anxiety. (4). When you’re busily engaged in something else, you feel less pain. Conversely, the more you focus on your pain, the worse it feels. Many people feel worse pain at night when there are no distractions.

Whenever my attention drifted back to my thigh, the pain increased.

PVOP means previous volume of pain

I’m using “volume” to mean two things: the amount of pain (cumulative over time) and its loudness (severity). The more pain you’ve experienced in the past, the more likely you are to feel pain – whether in the same body part or elsewhere. For example, migraine sufferers get more lower back pain and lower back pain sufferers get more migraines. And migraine sufferers get more RSI. And so on.

The more severe your pain has been in the past, the more likely it is to recur. If you’ve had severe lower back pain, you’re more likely to have another bout when compared with someone who’s only had mild lower back pain.

This is due to central sensitisation – when your central nervous system (your brain and spinal cord) becomes sensitive. This is an effect of neuroplasticity.

Your nervous system’s capacity to adapt is essential to learning. When neurons fire, they make firmer connections with one another, and those connections become more sensitive. So if you want to learn anything (like a new language), neuroplasticity is essential. Neuroplasticity is your friend – except when it comes to pain. Due to neuroplasticity, the more nocicpetion you experience, the more you’re likely to learn pain.

I hadn’t been stung in the thigh before. My previous experience of wasp stings was that they’re benign and don’t cause many problems.

My pain is much worse

You might think, “You only had a little wasp sting. My pain is severe and debilitating. It hurts!”

You’re right. Your injury/disease process and level of nociceptive input is different to mine. But the equation still applies. In extreme cases there’s a huge amount of nociceptive input. But they frequently don’t result in any pain  (at least, at first). Shark attack victims frequently state they felt something “hit” them, but they didn’t experience pain at the time. Perhaps partly because they didn’t know they had been bitten. Even losing part of a limb without any pain at the time. So, a lot of nociceptive input but no pain.

And at the other end of the spectrum, you can have severe pain with little or no nociceptive input.

XRay showing nail through booted foot

Photo by M.J.Fuller at wiki Radiography

The man with the nail through his steel toe-capped boot was in screaming agony. But the nail had passed between his toes, not even grazing his skin. And yet he was in severe pain.

Most people focus on what they imagine is the cause of their pain – “tissue damage”.  But that’s only the cause of your nociception. You expect the pain to have an entirely physical cause. But it doesn’t. No brain, no pain. Your brain has the final say, and determines how much pain you experience at any given time.

Look at the variables in the equation.

P = (N – MWP) + (NO – PO) + (ATBP) + (PVOP)

Most of them have nothing to do with “tissue damage”. But NO, ATBP and PVOP have a lot to do with threat. Leading pain researchers agree that the amount of tissue damage is a poor predictor of the amount of pain you feel (5). Remember the shark attack victims? If you don’t know you’ve been bitten, it doesn’t hurt as much.Shark-bite victims who see the fin approaching them before they’re bitten probably experience much more pain.

As for the poor embarrassed burly builder with the nail through his boot – his brain told him he had a nail in his foot. That’s a strong threat, so it hurt. A lot.

Threat has a huge influence in deciding how much pain you feel. It’s explained in detail in this review entitled “Associations Between Pain Appraisals and Pain Outcomes”(6) published six years ago in the Journal of Pain. It concludes:

        In sum, appraisals of pain as a source of potential damage or opportunity have robust associations with responses to acute laboratory pain and ongoing chronic pain. 

In other words,  if you feel threatened by your pain, your pain levels will be higher.

My equation helps people understand their pain better and come up with a practical plan to combat it. I hope it helps you.

Experiment with your own pain

If you have a persistent pain of your own, write the equation down. Then work out what you can do to boost MWP and PO. And then to reduce N, NO and ATBP.

Do let me know how you get on. And if you can think of a way in which the equation could be improved, I’d love to hear from you.

Gavin Routledge

Registered osteopath

About the author

Chief Back Officer at Active X Backs, in Edinburgh, Scotland.  (https://www.active-x.co.uk/). Co-author of “The Back Book” in 1997 with Gavin Hastings OBE, and author of “Active X Backs; an effective long-term solution to lower back pain” in 2017. Gavin graduated as a Gold Medalist (awarded for Conspicuous Merit) in 1991 from the British School of Osteopathy. He was Vice Patron of the British School of Osteopathy from 2005-2015, and a Director of the British Society of Lifestyle Medicine 2018-19. He has an MSc in The Clinical Management of Pain from the University of Edinburgh, and runs regular free webinars for those affected by lower back pain and sciatica.

  1.  Merskey H, Albe Fessard D, Bonica JJ, Carmon A, Dubner R, Kerr FWL, Lindblom U, Mumford JM, Nathan PW, Noordenbos W, Pagni CA, Renaer MJ, Sternbach RA, Sunderland S. Pain terms: a list with definitions and notes on usage. Recommended by the IASP subcommittee on taxonomy. PAIN 1979;6:pp249–52.
  2.  International Association for the Study of Pain (2019) IASP’s Proposed New Definition of Pain Released for Comment. Available at: https://www.iasp-pain.org/PublicationsNews/NewsDetail.aspx?ItemNumber=9218 (accessed 25 May 2020).
  3. Melzack, P.D. Wall PD. Pain mechanisms: a new theory. Science. 1965 [archived 2012-01-14];150(3699): pp 971–9
  4. Arntz, L. Dreessen, H. Merckelbach.  Attention, not anxiety, influences pain. Behav Res Ther. 1991;29(1):pp41‐50
  5. G. L. Moseley, D. S. Butler  Fifteen Years of Explaining Pain: The Past, Present, and Future. The Journal of Pain. September 2015
  6. Jackson, Y Wang, H Fan Associations Between Pain Appraisals and Pain Outcomes:Meta-Analyses of Laboratory Pain and Chronic Pain Literatures. The Journal of Pain, Vol 15, No 6 (June), 2014: pp 586-601