Introducing The Equation for Pain

podcast about lower back pain and sciatica.

I studied for a Masters Degree in The Clinical Management of Pain several years ago. You could say this is one of the spin-outs from that major step-up in my knowledge.

Before we dive into the equation, let me share a couple of images with you. Which man had more pain? The one with the nail in his head, or the one with the nail through his foot?

XRay with nail in head
Nail in head
XRay of nail through booted foot
Nail through foot

Credit: Google Images

The man with the nail in his foot was in screaming agony. The man with the nail in his head had no pain. Nail-guns are indeed dangerous. The twist to the tail? The nail through the booted foot had actually passed between the man’s toes, not even grazing the skin. And yet he was in agony.

And what about Phantom Limb Pain? When someone with an amputated limb develops pain in a limb that no longer exists.

The Equation will explain all. Are you ready? Here we go…

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

OK, let’s break this down.

P means the level of pain you experience

I don’t need to say much about this. Pain has long been defined by the International Association for the Study of Pain as “An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage“. After a long period of consultation with their international members, they are considering changing it to “An aversive sensory and emotional experience typically caused by, or resembling that caused by, actual or potential tissue injury“. Spot the difference? We’ll return to this later.

N means Nociception

Not a lot of people know this, but pain isn’t a hardwired system. You don’t have “pain nerves”. When something bad happens out there in your body, there are no “pain nerves” to detect it. There are nociceptors. Nociceptors detect noxious events. That could be physical trauma, extremes of temperature, or chemical changes (like inflammation).

When those things happen, the local nociceptors fire. Firing means sending a message along to the next neuron (proper name for a nerve cell). So nociception is a variable in the equation for pain. Broadly speaking, the more nociceptors that fire, the more pain you are likely to experience. But of course, it’s not just that simple…

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? There’s a good reason. The more movement you can do that doesn’t cause pain, the less pain you are likely to feel. The science behind this was first described by Melzack and Wall in 1965 – it’s called the Gate Control Theory.

When you move around, you stimulate other sensory neurons. They are called mechanoreceptors. They detect movement and mechanical pressure/load within tissues. When they fire, they block the nociceptor messages from reaching the next neurons in the pain pathways in your spinal cord / brain. Brilliant, isn’t it? TENS uses this system to reduce pain. TENS are those little units labouring women often use to reduce pain.

If you move around enough – some call it exercise – your brain will also release chemicals that suppress the pain system too. There’s still debate about whether endorphins or endocannabinoids should get the credit for this.

NO means Negative Outlook

If you are prone to depression or anxiety, or stressed, you are likely to experience more pain. Sorry. Don’t shoot the messenger, please. The pain pathways pass through the older parts of your brain. There they are interconnected with parts of your brain responsible for emotions and motivation. Your deepest motivating emotion is fear. It’s said that depression is worrying about the past and anxiety is worrying about the future. Worrying is fear. The more worry/fear you have, the more active this system is. And that augments any nociceptive input you may have. You see, the pain system and your emotional centres actually share neurons. So if fear is “firing”, pain is more likely to fire too.

There’s been a lot written about stress. But I like to describe it as fear that has or has not been acknowledged consciously. Fear that you won’t get paid this month. Fear that you’ll lose your job. Fear that you won’t be able to pay the mortgage for much longer. Fear that you might get sick. Fear that you’ll be one of the worst performers at work this month. You may not be facing those fears consciously, but if you look inside yourself, they’ll be there. They are there for me. I am currently stressed, and recently I’ve had more pain. Coincidence? I don’t think so. The only reason/variable? No, probably not for me.

PO means Positive Outlook

There’s a flip side. Fortunately, having a positive outlook can reduce pain. We’re back to your brain… Your brain releases certain chemicals when you’re enjoying yourself, or connecting with other people positively. They will reduce your pain. So, do things you enjoy. Spend time with people that you find uplifting. Especially if you can move at the same time. That’s why team sports, and dancing with a partner you really like, reduce pain levels dramatically. You’re combining MWP and PO.

ATBP means Attention To Body Part

The more you think about it, the more it’s going to hurt. Attention to pain has been shown to have a greater impact than anxiety. Think about it. When you’re busily engaged in something, you feel less pain. The more you focus on your pain, the worse it feels. Many people have worse pain at night. There are no distractions at night. So your brain focuses on your pain. Bummer.

PVOP means Previous Volume of Pain

Here I am using “volume” to mean two things. Amount (cumulative over time) AND loudness i.e. severity. The greater amount of pain you’ve had in the past, the more likely you are to have pain. That could be pain in the same body part, or it could be pain anywhere. So for instance, migraine sufferers get more lower back pain. Lower back pain sufferers get more migraines. Migraine sufferers get more RSI. And so on it goes.

The more severe your pain has been in the past, the more likely it is to recur.

Both of these facts are explained by something called Central Sensitisation. Have you heard the word Neuroplasticity? It refers to your nervous system’s capacity to adapt. This 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 painful experiences.

It turns out that neuroplasticity means the more nocicpetion you experience, the more you are likely to learn pain. That is Central Sensitisation; when your Central Nervous System becomes sensitive (the CNS is your brain and spinal cord). Double bummer.

Summing up

So from the equation, you can see that these factors make your pain worse:

  • More nociception
  • Inactivity
  • Anxiety, depression, stress, catastrophising (making a drama out of a crisis)
  • Attention to the sore bit
  • More pain in the past

And, on the other side, these factors will lessen your pain:

  1. Movement that doesn’t hurt – especially vigorous movement
  2. Being with friends
  3. Having a good time
  4. Keeping busy on things that take you away from focusing on your pain

Let’s return to the IASP’s current (at time of writing) definition of pain: An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.

Many people focus exclusively on what they imagine is the cause of their pain – “tissue damage”. Whereas it’s only the cause of their nociception. They expect the pain to have an entirely physical cause. But it doesn’t. I like to say “No brain, no pain”. That may seem like a pointless and pedantic thing to say. But I’m trying to make a point. It’s your brain that has the final say. The brain determines how much pain you will experience at any given time. Look at all the variables in the equation.

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

Most of them have nothing to do with “actual tissue damage”. NO, ATBP and PVOP have a lot to do with threat. Many leading pain researchers agree that the amount of tissue damage (and therefore nociception) is very poorly correlated with the amount of pain you feel. Remember the builder with the nail in his head? Turns out he didn’t know he had a nail in his head. It must have happened on the building site when he wasn’t wearing his hard-hat. He may have felt an impact, but perhaps he was massively engaged with something else at the time. Either way, he didn’t have any pain.

As for the poor embarrassed burly builder with the nail through his boot… Well, his brain told him he had a nail in his foot. That’s pretty threatening to your well-being isn’t it. So it hurt. A lot.

So threat is much more influential in deciding how much pain you feel. If you have the stomach for it, read this review entitled “Associations Between Pain Appraisals and Pain Outcomes” published 6 years ago in The Journal of Pain. The conclusion finishes “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.” If I’m not mistaken, that is science speak for “if you feel threatened by your pain, your pain levels will be higher, in the lab and in real life.”

If you’ve made it this far, well done. I’m sorry it’s been a long read. But here’s the pay-off. Knowing all of this can set you free from the fear/threat of pain. Pain is always there for a reason. You just have to work out how much each of these variables is a factor for you. And do something about it!

So, why does my back hurt when I sit at my computer?

This was never meant to be a “6 tips to relieve your pain” sort of article. But I’m conscious of the title of the article – “Why does my back hurt when I sit at my computer?” And because I’m a clinician, I just can’t help finishing with this proposition for you:

Maybe your ligaments, muscles, discs etc are tired of being loaded in the way you’re loading them. Maybe you’ve been sitting still for quite a while, and you’re running low on those mood-enhancing chemicals. Maybe you’ve got a lot on your plate, or you’re working to a deadline, or don’t like this task. Maybe you just hate your job. Maybe having a sore back sitting is a very common experience for you. Maybe your Dad – and his Dad before him – had a “bad back” and you think you have too. And you just can’t help thinking about it. And worrying that there might be something really bad going on back there…

Then again, maybe it’s just your back saying “Move!!”