Pain science: Part 2: How Does it Happen?

Pain Science Part 2: How does it happen?

This is finally a continuation of the previous post entitled Pain Science Part 1. As you already know, I am very excited to introduce this and hopefully be able to explain pain in relatively simple terms. The last post talked about what pain is and what pain isn’t. Now it is time to explain why we experience pain and how it all happens. Let’s start peripherally.

Input to the system includes:


  • There is no such as a pain fiber. Tissues contain nociceptive fibers which are not pain fibers. They contain danger receptors- not pain fibers.
  • We don’t conduct pain in the periphery. We experience pain through the brain.
  • The tissues send signals to the spinal cord then up to the brain, the brain decides to call something painful or not based on its overall threat.
  • For example: If you sprain your ankle in the street you experience pain. If a bus is coming the brain will reduce the threat of the sprained ankle and make you move to get out of the way of the bus. Once you are in the clear, the pain comes back because this is the highest threat to the system.
  • Pain does NOT come from the tissue itself!
  • Another example: arthritis. Arthritis does not cause pain. How many patients have you had with, let’s say back pain, and when you have them perform exercises you can hear their knee crunching but they experience no knee pain. Pain is NOT from the periphery.

Peripheral nervous system

  • The PNS sits right below a threshold baseline. The input from the PNS either fires at a rate higher than threshold which is sent to the spinal cord or it fires just below baseline in which no response is sent further on into the system.

The injury:

  • All nerves are myelinated. When an injury occurs these myelinated axons become unmyelinated.
  • At the dorsal root of the spinal cord, ion channels are formed from DNA/mRNA and then travel down axon plasma and insert into specific areas that are unmyelinated.
  • After an injury, these ion channels form at the injury site. For example, if you develop a stress fracture/reaction in your tibia this causes a decrease in myelination-> there will then be an increase in ion channels in the area.

Ion Channels:

  • Channels open and close based upon a whole host of other influences:
    • Temperature, stress, movement, immunity, blood flow
  • They are always in a balance and if there is an increased input from one of the influences it will open the channel and send chemicals up the axon to the spinal cord.
  • For example, stress reaction= ion channels= cold temperatures= increased activity in the spinal cord. This does not = pain. Pain will be determined by the brain
  • If you are more stressed about the injury then the signal to the spinal cord will increase. If you are sick and also have this injury then there will be an even larger increase in signal to the spinal cord.
  • Ion Channels have a half-life of 48 hours. They are replaced naturally by neuroplasticity.
  • The signal is sent via chemical release from the ion channels opening. They fire in both directions. If the ion channels keep opening then chemicals are continually released to the spinal cord and can have long lasting persistent effects that have nothing to do with the current injury.
  • By educating the patients about pain, we can down regulate the system and decrease the activity of the ion channels and therefore decrease the chemicals released.

The Spinal Cord:


  • The chemical released by the ion channels travel to the dorsal horn of the grey matter of the spinal cord.
  • These then are picked up by the spinal interneuron
    • The job of the interneuron is to determine what gets inhibited (stopped there) or what gets relayed up the spinal cord to the brain.
  • There are two fibers that come into the spinal cord
    • A-fibers which regulate everyday light touch activities like the feeling of your pants against your skin
    • C-fibers which are the nociceptive fibers that will alert to danger
  • The interneurons will then take the inputs and determine if the threshold is met and then either send the signal on or stop it there.
  • There is a convergence of information at this point. Not only from the left side and at the L3 level but also from the right side and everything below that level because it receives information from each segment.
    • This is why many people with chronic pain will have a bilateral presentation.

Chronic pain/sensitization

  • Persistent firing by the ion channels cause increased chemicals to be released at the dorsal root of the spinal cord.
  • This causes increased input to the interneuron, increased above thresholds signals relayed up to the brain and therefore consistent awareness down the chain at the site of the tissue.
  • This persistent input can degrade the interneuron and this also can then affect the levels around it because they are receiving even more input due to the lack of one of the levels not regulating the input.
  • These DON’T regenerate!
  • The A-fibers then begin to grow more and now light touch becomes an issue leading to difficulty with discrimination of your left/right sides.
    • Mirror therapy!

The Brain:

  • There is no pain area in the brain!
  • Some common areas light up but the pain experience is a combination of multiple inputs from multiple areas of the brain.
  • On brain imaging from fMRI, chronic pain patients have a brain that is very alert and hyperaware. There is too much going on! If our goal is herniated disc -> pelvic tilt -> and we make them think that they have to maintain this all we are doing is increasing input to the system that is already overloaded
    • On a side note: chronic pain and abdominal exercises. No, they usually aren’t “weak” but actually they are already co-contracting too much. If we focus on this even more then all we are doing is scaring the patient into thinking that they are too weak and this will increase the system even more! We need to down regulate!
  • Typical Pain Nueromatrix taken from A. Louw (these are the areas that light up the most)
    • Premotor cortex/motor cortex
      • Movement
    • Cingulate cortex
      • Concentration and “fog”
    • Prefrontal cortex
      • Memory
    • Amygdala
      • Fear and addiction
    • Sensory cortex
      • Right and left discrimination, joint position
    • Hypothalamus/thalamus
      • Stress responses, chemical output and motivation
    • Cerebellum
      • Movement and fine motor control (ie. Those patients who can’t even perform those simple lift leg up exercise)
    • Hippocampus
      • Fear conditioning
    • Spinal cord
      • Peripheral inputs
    • As you can see from the above list, increased input from the spinal cord influences all of these areas. Think about your patients who are too tired to get out of bed, who are too fearful to move, lack motivation, have a difficult time even with simple tasks, etc
    • If a patient has difficulty with simple tasks because the brain is too active and that area has such a low threshold. The communication between the brain and the body is impaired. This can lead to those imbalances and poor movement that we see.
      • Not necessary weak but rather inability for brain to focus on that one specific movement

The output:

  • The brain puts every other system on hold except for the most important ones. It decides this based upon threats. If one threat is larger than another then this system will take precedence.
  • The brain releases a whole host of chemicals in response to the perception of a threat/pain
    • Adrenaline
      • Stress chemical (see below)
    • Cortisol
      • Shunts blood and can make tissues sore/tired/sensitive/fatigued
      • Impacts sleep, memory, concentration
      • Increases nerve sensitization (ion channels), persistent inflammation (makes the body think that an area is still injured when not thereby increasing sensitivity to an area), and general malaise.

In summary:

Once you understand that the brain controls everything. Questions begin to answer themselves. For instance, general “patella femoral” knee pain. We can all agree that the research shows an impaired onset of the activation of the VMO versus the other quad muscles. But why? Well, if you believe that the brain truly runs the system, then you have to believe that there is a reason for it. Not because there is pain there. Pain is not there! Pain is in the brain! So if you have someone that collapses in with running and there medial knee is painful with a reduced VMO activation (we can’t measure this in clinic). Then look further. If there is a dynamic valgus then the patella no longer needs to track medially. It make sense for the patella to stay in the groove and this would be best accomplished by activating the vastus lateralis first. The problem would be at the hips and proper control over the musculature in that area. This does NOT include just SLR 4 way and call it a day but much more.

If everything is regulated by the brain then so is manual therapy! Yes, we like to think that we are doing this awesome adjustment. But really all we are doing to sending a neurological feedback into the system which hopes to “reset” the system. At least give us a way in. Watch the Medbridge Chad Cook cervical lecture and he points to some great research showing the chemical effects that manual therapy has and the short time effects if it.  I will also go into how to explain it to patients (creating handouts soon) and also what this means in respect to different cases and “painful” experiences.


I really like to use pain science to better understand what we do as therapists. But it should never be used alone. There is always something we can do to help the patient. Use reset systems (like Mackenzie, mulligans, any manual therapy), use proper words and also improve movements. Give the patient hope and a purpose to getting better.

~ TJ Slowik

Thank you to Adriaan Louw for one of the best continuing courses I have taken (through medbridge).

Thank you to Adriaan Louw for one of the best continuing courses I have taken (through medbridge).


Pain Science: Part 1…

Pain Science Part 1

Pain science is a topic that I really wanted to discuss since I started this blog. Much of what I do nowadays refers back to pain. Our job as therapist is to treat patients who are in pain. It is what we do. It is why we get paid. The end product of every patient that walks through that door is to relieve their pain and to improve function. They are dependent on each other. Do you really think that a patient will be happy with the care if there is not a pain reduction? Probably not even if they can function normally. They came to us to help their pain. Then why do most therapists not know what pain is? Where pain comes from? Many therapists, and I did for a long time, feed into pain. We give it life. We make it worst with our words and demeanor. I hope that, at the least, what you can take away from this is to not feed into the pain. To debunk the common myths about pain so that you can communicate that to your patients.

Pain education isn’t only important for chronic pain but also for acute pain. All pain does start at some point. Hopefully, if we can educate our patients early on in the process we can begin to change the onset of chronic pain. Take a patient, who may be at risk for developing chronic pain (many reasons for this), and help to reduce the effect that pain has on their future self. Like most other “interventions” it is not best to memorize the information but rather to learn the concept. You can apply an intervention to a handful of patients but you can apply a concept to every patient. Learn the concepts of what pain is and what pain isn’t. Learn how to properly explain pain to patients. It changed my career path and I hope by at least starting this conversation with you that it will do the same.

There are many avenues to learn more about pain. The first is research of course though it is harder to find in the US versus other countries who push out a lot of research about pain (if looking for research just look at Moseley and all the research that he puts out). The US seems to be focused on this drop step/jump down and rehashing old and abused research material. Honestly, do we need another research article on a step down task or jumping tasks to know that faulty mechanics equal ACL tears/other injuries? What we need is more research on the rehab behind this and proper exercises that will improve this functionally and not the same old 4 way SLR with some planks thrown in for good measure. The second area that I have learned the most from and is where much of this talk comes from is Medbridge course by Adriaan Louw called “teaching people about pain”. If watching this course doesn’t completely change your practice re-watch it and really try to learn the concept. Not the individual parts. Thirdly, are the blogs. In the margin I have a lot of blogs that I follow. All experts and clinicians that I admire. If I become half the therapist that they are my career will be a success. Some of the ones that I like the most for pain:

  • Noijam and
  • Body in Mind.
  • Forward Thinking PT
  • Explain Pain

Yet, all of them have some type of pain related education involved in their postings.

So why is pain science important?

Chronic pain has doubled in the last 15 years and continues to be a growing problem in the clinic. Chronic pain itself can be hard to define but for simplicity we can give it a quick definition of pain that the patient is perceiving that has lasted longer than the healing phase for the original acute injury (though ~ 30% of chronic pain doesn’t have a related injury). Treating chronic back pain isn’t always about targeting core musculature or activating the TA or giving heat/stim and “cracking” them. It starts way before any intervention that you want to give. You must treat their fear and beliefs first.

Fear can be defined as a distressing negative sensation induced by a perceived threat. The fear of pain is worse than the fear itself. The circle of fear is something like (from Vlaeyen, Linton 2000)

Injury -> Pain experience -> no fear -> confrontation -> Recovery OR

Injury -> Pain experience -> Fear from lack of knowledge/medical tests/words/internet -> Pain catastrophizing (irrational thoughts) -> pain related fear -> avoidance -> depression/anxiety to move/disability -> feeds back to the pain experience again.

This is where we need to educate them and stop that second loop from starting acutely or move them out of the second loop.

Many patients in pain have impaired beliefs about pain such as:

  • Pain is always bad and pain equals injury
  • All pain must be gone before engaging in normal activity and movements
  • Pain will increase with all activity/any activity
  • Passive treatment is the best
  • I have to live with pain the rest of my life

We feed into these beliefs by using our words. These words include any medical test findings such as arthritis and bulging discs, something is out of place, your posture is bad therefore you will have pain, you have a weak core or you are “unstable”. I am not saying that some of these don’t happen or that we shouldn’t treat what we see as deficits but rather we need to pick our words better. They are very abrasive words and telling someone who sits all day that there posture is causing their pain then that will only increase the hyperactivity of the entire system every time they sit!

Our educational systems feed into these beliefs as well. It is hard to change something that you learned in school and then practiced when you graduated. It is not easy to start to change your thinking. Believe me, I know! It is a small steps each day to change the way you think about pain and change the way your patients think about pain. It is hard to drop this biomechanical model/patho-anatomy model of pain in lieu of something that you can’t see! Once again, I am not saying to drop the entire system and only think about pain. That is not at all. But question what you have been taught and why things happen. I use the biomechanical model with pain science to explain the reasons why the brain could be perceiving outputs as pain or to explain the original injury. I am very much biomechanical based but adding pain to the whole picture actually clears up so any questions that I have. [Look at “explanatory and diagnostic labels and perceived prognosis in chronic low back pain” by Sloan/Walsh 2010 Spine.]

Definition of pain: “Pain is a multiple system output, activated by the brain based on a perceived threat” (Moseley via Louw)

Lorimer Moseley performed a study on someone with 4.5 years of pain. Pain started as LBP then became widespread in lower extremities. Using an fMRI they measured brain level activity. On evaluation the fMRI showed severe hyperactivity of the brain. Then they educated on spinal stabilization exercises for one week. There were improvements! But mild! There was a small change in hyperactivity of the fMRI. Then they educated patient for 1 session on pain and did nothing else. What happened? Severe decreases in brain activity. Pain education decreased pain much more than any spinal stabilization exercises. I know that it was just a single subject but isn’t that enough to warrant a longer look at it. [Moseley 2005. Widespread brain activity during an abdominal task markedly reduced after pain physiology education]

There are more: A couple of systematic reviews on therapeutic neuroscience education from Clark and Louw that also show marked improvements in chronic pain. Lorimer Moseley/Body in Mind have plenty of articles to keep you busy.

Tissues and pain

  • Tissues due to get injured! But they heal!
    • And even shown that disc bulges reabsorb in one year.
  • Tissue injury does not equal pain
    • I have read anywhere between 40- 60 % of people have a disc bulge with no pain
  • Arthritis does not equal pain
    • Arthritis is one of those bad words. Patients feel doomed by the thought of having arthritis and become afraid to move. How terrible that is. The one thing that will help them they become afraid to do inciting a hyperactivity throughout there CNS.
  • Cool study on “neck pain in demolition derby drivers (Simotas, Shen. 2005)”
    • Shows only a 2.5% chronic neck pain
  • Shoulder after rotator cuff repair. MRI imaging findings in asymptomatic individuals (Speilmann 1999)
    • 90% showed abnormal signaling and 16% had partial tears while 20% had complete tears

In my next post I want to go through the pain process. How pain develops and where it comes from. I am going to review the basics from what I have learned.  I have many more research articles which I think that I am going to review as a group after the next post.

Final thoughts:

Like I said above, and I want to reiterate. I know, that in order to treat patients, we need to look everywhere for the possible reasons why someone is in pain. Sometimes it is simply fixing the mechanics to take pressure of an area. Yet, it is also, fix the mechanics to take the pressure off an area and have a neurological input that decreases the hypersensitivity of the nervous system/brain. Think more! Challenge yourselves to go above the standard treatments for people in pain. Remember: we go to work and then leave work but patients come to clinic in pain then go home and there pain continues. For many of our patients the pain never ends. Think about that! Pain that never goes away. Think of a time that you had pain from an activity (as most PTs were athletes at some time we all have them) now think about it being there all the time and every day for years. That is what many of your patients experience.

~ TJ