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Blog Post

How do we explain pain that comes and goes?

We have known for decades now that pain is a very complex thing. Pain can emerge with or without corresponding tissue damage. When there is tissue damage, pain is usually not very well correlated with the extent of the damage. Two people with the same tissue damage can experience quite different levels of pain. And consider how much a paper cut or wasp sting can hurt even though the actual tissue damage is minimal.

Nevertheless, many people assume that if they are having pain there must be some new or ongoing injury to explain it. I will use spine pain as an example because it is so familiar and yet so perplexing to most people. You may have been told your back pain is coming from a bulging disc. We’ll ignore the fact that is a pretty uncertain statement (e.g. many pain-free people have bulging discs, it is extremely difficult to pinpoint the source of back pain with any certainty, blah, blah, blah) and assume it’s true for the sake of argument. That disc bulge should be pretty well healed after 8-12 weeks. If it continues to hurt after that time, what explains it?

If you “throw your back out” again 6 months later, is that you reinjuring your disc? Anything is possible, but if you fully recovered in 14 days and not 8-12 weeks then you should question whether it was really injured. So what caused the pain?

Rather than think of pain as having a one-to-one connection with injury, we need to adopt a better understanding of what causes our symptoms. We recognize that there are many variables that can go into having painful symptoms, or other types of protective sensations like stiffness. A good way to understand and visualize how these variables interact to create symptoms is a “vector model”. Physical therapist Matthew Low did a good job of explaining this idea here, but I will attempt to give it to you in brief.

Let me take you back to physics class (briefly, I promise). A vector is an arrow that represents some force that has a direction. The longer the arrow the higher the force it represents. Importantly, vectors representing several different forces can be added together to give you the resultant force and the direction it goes. Thus you can see how several forces can interact to create the one force you see.

We can use the same concept to visualize how many variables in your life and body can interact and result in pain.

We’ll return to our back pain example. Some things are factors that increase the risk of back pain. Let’s say being very sedentary, past injury, fear avoidance (not doing a particular movement because you think it will hurt or injure), depression or anxiety, hypervigilance (often leading to excessive, unnecessary muscle contraction), job stress, poor sleep, and poor muscle fitness. These will be represented by arrows that tend towards back pain.

Some things may decrease the tendency towards back pain like positive beliefs about getting better, an enjoyable exercise program or physical activity, and good social support. These will be represented by arrows that tend away from back pain.

Every person will have their own such factors. The amount that they contribute to or detract from the back pain will be different, so the arrows will be different lengths.

Now we have a chart that looks like this. The arrow at the bottom is the result of adding the lengths of all the arrows up. The more and longer the negative arrows, the more likely one is to pass the threshold and feel symptoms. The more and longer the positive arrows, the more protected one might be from experiencing symptoms.

Looking at this, perhaps you can start to understand why some days you feel no symptoms and other days you do. If one or several variables increases quite a bit—say you have a bad day at work and a poor night’s sleep—you may experience back pain, even if you didn’t increase the stress on your back at all.

This can really help us understand the ebb and flow of conditions like back pain. Increase a few of the negative variables and suddenly you get that pain “out of the blue”. Once we might have attributed that to a new injury, but most likely you just crossed that threshold. A few days later, some of those variables can get smaller, the resultant arrow passes back over the threshold and your pain goes away.

Hopefully viewing painful conditions in this way makes you recognize that you have some control. You can make some of those negative variables smaller through activity modification and lifestyle changes, and you can choose which are the easiest or the most convenient to change. You might also decide to tackle the largest arrow first. Additionally, and no less important, you can increase the size of the positive arrows to counteract the negative factors. Now you have options for how you can treat yourself and control your condition. It doesn’t always have to be what the physical therapist tells you to do. If you despise exercise, you may still be able to reduce your pain by addressing other factors (but I still think exercise has huge bang for the buck.)

There are other helpful suggestions about treatment that you can glean from this model. If the resultant arrow passes the threshold line by quite a bit, you can make two important deductions. One, is that changing just one thing may not be enough to reduce your symptoms. For example, if you have untreated or poorly-controlled depression but choose to ignore it and instead focus on increasing your core endurance you may not notice any positive effect. You will probably want to address the biggest contributing factors, and you may need to address more than one. The second deduction to be made is that your rehabilitation will likely take a fair amount of time and require you to be persistent with the changes you deploy.

Viewing the model will help you identify not only those things that you can change, but also those things that you cannot or will not. If you had a previous back injury, you can’t change that. If you have pain at work and you’re a construction worker but can’t change your job or don’t want to, then that variable will always be there.

The model also lets you see when you may need help from more than one specialty. As a physical therapist, I must recognize that my realm is mostly related to activity modification and exercise. If you have a mood disorder, or a serious sleep disorder, or you’re stressed because you’re struggling to make ends meet at home, those are things that must be addressed by the appropriate professional. Ideally, all of us professionals would coordinate to help you.

Lastly, this model can be applied to any and all pains and injuries, not just back pain, and not just pains that come on without an obvious injury. It could be knee arthritis. It could be shoulder surgery. It is important to recognize that increases in any of the variables can bring pain on again and your battle to remain pain-free may require lifelong vigilance in some cases. But viewing your pain in this way should give you confidence that you can manage your condition in a variety of ways. With the proper guidance, you can be put back in control.