Practical Science on Movement and Pain
Practical Science on Movement and Pain
This weekend I went to Portland, Oregon to attend a conference sponsored by the APTA Section on Women’s Health, featuring talks by Lorimer Moseley and Paul Hodges on the issues of chronic pain and motor control. It was a fantastic experience, and most of the time I was buzzing with geekcitement.
Jealous you missed it? Don’t worry I will summarize the highlights. This post will address the talk by Lorimer Moseley.
First of all, I should point out that Lorimer is an extremely engaging and humorous speaker. And a total character as well. How can I describe him?
He’s kind of like a rough cross between Steve Irwin the crocodile hunter and Austin Powers. An international man of mystery/naughty school boy with a thick Aussie accent and huge enthusiasm.
Even though this guy has taught neuroscience at Oxford, he lectures about it like a guy reviewing a rugby game with his mates at a pub. One day he lectured in a dress. Oh behave! (Of course he did that to raise money to help girls in Sierra Leone attend school. Good on ya mate!)
OK enough with the personality. What did he talk about? Here is a summary of the main take aways for me.
If there is only one lesson to be learned from the talk it would be that nociception (often erroneously referred to as pain signals) does not equal pain. Here’s the difference.
Nociception is defined as activity of high threshold Adelta and C nerve endings, which are designed to detect mechanical, thermal, or chemical changes in the tissues.
Pain is defined as a conscious unpleasant experience designed to evoke a protective response.
Although nociception is an input to the brain that often results in the output of pain, the brain considers many other inputs before deciding to create pain, some of which may be far more decisive than the level of nociception. In fact, nociception is neither sufficient nor necessary to create pain. In other words, you can have pain without nociception and nociception without pain.
Before the brain creates pain on the basis of nociception, it will essentially ask a key question: how dangerous is this really? To answer that question, it will consider many different kinds of inputs, which can be divided into four basic categories:
1. proprioception (information from joints, muscles, tendons and skin about the positions and movements of the body parts)
2. interoception (information from nociceptors about the thermal, mechanical and chemical condition of the tissues)
3. exteroception (the five senses)
4. cognition (knowledge, memory, feelings, perceptions, belief, logic, attention, expectation, etc.)
If the brain processes the different inputs and concludes that some form of protective action is necessary, it can choose between several different kinds of protective outputs, such as pain, immune responses (e.g inflammation) or protective movements such as flinching, limping, muscle guarding, stiffness and other motor control changes. (Now which kind of protective output would you rather have, movement or pain?)
One important point to consider is that any output will almost immediately become a new input into the system. For example, a protective movement will modify the proprioceptive and exteroceptive inputs to the brain. Pain will create new thoughts, feelings and knowledge about dangers to the body. Inflammation will sensitize nociceptors. And so new outputs are created which then immediately become inputs again.
The point is that this is an incredibly complex and dynamic system that loops back on itself every second in an unpredictable and inherently personal and individualized manner. To illustrate this, Lorimer asked us to consider several simple scenarios and to write down all the inputs and outputs which might be involved.
For example, let’s assume that some guy bends forward in a way that activates mechanical nociceptors in the low back. How does the brain weigh this information and decide whether this is a dangerous event that requires pain for protection?
The brain will consider all the inputs, and there are many. Proprioceptive and exteroreceptive information will report the positions of all the different body parts and whether they are controlled and balanced. Perhaps they will provide information showing that balance is very poor and that a fall may be coming. Perhaps cognition will report that this is the exact same position the body was in last year when it experienced extreme back pain that lasted for several weeks. Maybe another part of the brain remembers that a doctor once told him he has a bulging disc. Or a physical therapist told him that forward flexion is a great way to blow out a disc. Maybe other cognitive inputs will report that he has just lost his job and has no way to pay for medical care.
Will this person have the same pain experience as someone else who has the same level of nociception, but who moves with good balance, has never had back pain before, is not afraid of movement, and has excellent financial and social support? No way!
Lorimer told a great story that illustrated the power that cognitive inputs can have over the output of pain. He once worked with an elite biker who had back pain with riding. After a great deal of progress, she could ride the flats but was still experiencing pain while climbing hills. Most therapists would assume that the problem with hills was related to some mechanical factor that comes into play when the relationship to gravity is changed.
But Moseley was curious whether hill climbing was problematic for visual or cognitive reasons. So he set up some cameras on a bike treadmill in a way that created an illusion of hill climbing for the rider, even as she rode over flat ground. She immediately reported back pain, based solely on the new visual input. After it was explained to her that this was an illusion, she regained the ability to climb without pain. Apparently the recognition that her pain was not caused by a mechanical factor modified her cognitive inputs in a way that convinced the brain that hill climbing was not dangerous.
Cool stuff huh? Actually nowhere near as cool as the rest of the talk, which I won’t be able to get to until another day or two. See you soon, mate!
Click here for part two.
If you want to read more about pain and some of Lorimer Moseley’s research, check out some of the posts below: