Published October 12, 2020
It’s long been assumed that chronic musculoskeletal pain – the persistent pain felt in the muscles, joints, ligaments, tendons, and bones – is directly correlated with the amount of damage to those tissues. People with musculoskeletal pain conditions such as low back pain, arthritis, whiplash, and fibromyalgia often make this assumption, believing that the more severe the injury, the worse the pain will be. As a result, they are often loath to exercise or participate in physical therapy to better manage their pain.
Yet, research has consistently demonstrated that musculoskeletal pain and tissue injury do not have the one to one relationship so commonly supposed.
Pain is actually a “very poor measure of tissue damage,” said Romy Parker, a pain researcher and physiotherapist at the University of Cape Town in South Africa. “Certainly, all pain is real, no matter what is causing it. But while a person may be in pain and feel terrible, it doesn’t necessarily mean that there’s anything dangerous going on in that person’s back, neck, or ankle, wherever they are feeling the pain. That’s why teaching people that pain doesn’t necessarily equal danger, and why that’s so, is critical to helping them do the things they do to best manage it.”
Given that the extent of tissue damage does not necessarily explain the degree of pain, what does? To answer that question, researchers are pointing to the need for a better recognition of how the body integrates multiple sensory inputs to create the experience of pain, as well as to the importance of education, both about the pain system and about the benefits of movement and exercise. By going beyond a narrow focus on the body, and by increasing the understanding of all of the factors that contribute to musculoskeletal pain, the possibility of better outcomes for people who live with pain will emerge.
A whoosh and a creaky door give insight into the experience of musculoskeletal pain
Pain is often described as a warning signal that alerts a person to the risk of tissue damage upon further movement or action. Yet, according to Tasha Stanton, a pain researcher at the University of South Australia in Adelaide, the experience of pain results not only from an electrical signal from the nerves in the injured tissue but also from the integration of information from numerous sources in the brain.
“The pain you feel is the result of the integration of a lot of different information: the situation you are in, the feelings you have, the beliefs you hold, and your past experiences. It’s so much more than just what is physically happening in a particular body part,” Stanton explained. “The brain is actually quite good at taking shortcuts, which is good for survival, but, when it comes to pain, the nervous system often links things together in ways that can alter your perception of what is occurring in your body and what you feel.”
For example, in a 2017 study, using a customized device called an indentor, Stanton and colleagues applied varying degrees of pressure to the backs of people living with chronic back pain, They paired the pressure with one of two sounds: either a creaky door or a gentle “whoosh.” Stanton discovered that when individuals heard the creaky door sound, they significantly overestimated the pressure applied to their spine and reported feeling more back stiffness, in what she called an “overprotective” response. Conversely, when they heard the more soothing “whoosh” sound, they reported the opposite, underestimating the pressure and feeling less stiff.
“The data suggest that those sounds were integrated with the pressure information and interpreted as giving additional information about the state of the back,” she said. “What’s so powerful about that finding is, most of the time, this kind of thing is completely outside of our awareness. But, as researchers, we can bring these perceptual changes into awareness; we can play with different inputs to see how our perception of pain or stiffness might be changed by them.”
In a 2018 study, Stanton and colleagues reported similar results when they used computer technology to “resize” the knees of people living with knee osteoarthritis. Here, participants wore head-mounted displays that made it appear as though their knee was either being stretched or shrunk. As with the paired sounds, these visual changes altered an individual’s pain perception.
“We actually tested a lot of different illusions but what we found was that illusion conditions that induced a credible resizing of the knee joint were analgesic [pain relieving]. We saw quite a sizeable reduction in pain levels, on the order of 30-40%,” Stanton said. “It’s only a temporary reduction in pain but it suggests we have powerful, innate processes at work in the nervous system that influence what we feel.”
Those processes may even have the power to change the body’s physiology. Stanton said that the visual illusions led to a change in actual swelling in the knee of one of the study participants. It was a surprising result and one that her team decided to investigate further in a case study of this person.
“We performed one of the stretch illusions and his knee just swelled up before our eyes,” she said of the earlier study. “He was lovely and was willing to come back to see whether or not we could reliably manipulate the level of swelling, and it turns out that we could. When we did the stretch illusion on his knee, it reduced his pain, but it made his knee swell. When we made his entire leg look very small, both his pain and the swelling were reduced. The complexity of it all just blew my mind. In this case, we saw that the sensory systems were interacting with the processes involved in physiological regulation of the body.”
That particular case report adds an additional layer of complexity to the issue of multi-sensory integration and pain: different people respond uniquely to the same sensory manipulation. Stanton said that she and her team see a remarkable amount of individual differences in most of their studies.
“In the knee resizing study, some experienced pain reduction when we resized the joint by stretching it. But for others, shrinking the knee joint was analgesic,” she explained. “We don’t quite understand why we see those differences, but they are quite consistent within an individual.”
Taken together, Stanton said, all of these multi-sensory effects have profound implications for treatment of musculoskeletal pain and for how patients with different musculoskeletal conditions can better manage their pain. For example, each person may require a slightly different approach to find the relief they seek – and it’s important for clinicians to understand that. Furthermore, Stanton said, people with pain will benefit most from this improved understanding if they grasp the myriad factors that can influence their perceptions. Education is important.
“Your pain is not a read-out of what’s happening in the body tissues. It’s the integration of numerous sensory inputs, as well as your beliefs, the environment you are in, and your past experiences. It all matters,” said Stanton. “I would argue that we now understand that pain is a protective feature that occurs in response to either real or perceived danger. And there are so many cues around us that can influence whether our nervous system is primed toward protection, including sensory cues. This understanding – that pain is about protection rather than about tissue damage – has importance when it comes to clinical care. Because people’s thoughts and beliefs about pain can contribute to the system being overprotective, we need to be having deeper, more nuanced conversations with patients about how pain works, what factors can influence it, and how it all comes together to create the perception and experience we have.”
The truth about pain leads to a revolution
Not having a proper understanding of the complexity – and flexibility – involved in how the nervous system constructs the pain experience means there is a higher risk of becoming “overprotected” by pain, said Lorimer Moseley, a pain researcher at the University of South Australia who has worked with Stanton. When Moseley first started out as a physiotherapist, he said he was surprised to see that when he educated his clients about the nervous system and pain, they would have better outcomes.
“What I saw was a stable, predictable relationship between understanding and pain,” he said, explaining that an understanding of the underlying neurophysiology seemed to be of benefit to his patients. “I wanted to understand my own clinical observations about this – what was the most important thing I could do, as a physiotherapist, to help people improve?”
In some of his early research, Moseley and colleagues compared education about the neurophysiology of pain with more traditional “back school” education in people with low back pain. In this 2004 randomized, controlled trial of 58 patients living with back pain, the researchers found significant improvements in several measures related to how people think about their pain as well as on a forward-bending task after participants received the neurophysiology information. This suggested that an overprotective system could be retrained to improve both function and quality of life for those who live with persistent pain.
“The control condition was basic stuff about protecting your back, ergonomics, lifting strategy, disc herniation, all that sort of stuff,” he said. “As a naïve researcher at that point, I was surprised to see that talking about the complexity of the nervous system seemed to work better for people. The content was relevant to recovery and helping people do the things they needed to do to feel better.”
In the years since, Moseley has worked to understand the nuances of neurophysiology education and pain, including what kind of language, as well as other factors, can best help those who live with chronic musculoskeletal pain conditions engage in evidence-based interventions, like exercise and physiotherapy, to make improvements. The work remains ongoing. His ultimate goal, however, is to help people “truly understand just how amazing and adaptable the human organism is.” That’s why he created Pain Revolution, an organization that provides both patients and clinicians with evidence-based resources to improve pain education across Australia.
“We are learning that we can really make a dent on this massive problem – the costs and disability from chronic pain conditions really are just massive – when we can help people better understand what pain is and how it works,” Moseley said.
As a graduate student working with Moseley, Dave Moen, of Form Physiotherapy in Adelaide, worked on developing another engaging pain-related educational resource, Tame the Beast. As a physiotherapist, Moen wanted something that would help people understand the value of exercise for long-term management of their pain. There are now dozens of studies showing the value of regular exercise for improving chronic musculoskeletal pain. Yet, Moen said, when people feel pain, trying to get them to do physiotherapy or regular exercise can be a hard sell.
“When people with pain move more, they develop greater physical capacity and strength, and that can help reduce their pain levels over time,” he said. “But when people believe that pain equals damage, they are less likely to move because they are feeling pain when they do so. We wanted to develop resources so people can understand that pain is not necessarily a sign of damage, so they would be more likely to exercise and do the things they should do to help them recover.”
Moen developed online courses for people with pain and for clinicians called Permission to Move to help inform both groups that doing exercise will not cause harm. And even if exercise may feel a bit overwhelming at first, sticking with it has long-term benefits.
“The idea is that, if you’re in a dark room and go outside on a normal day, it can seem very bright because of the differences in the two environments,” Moen said. “If you’ve been at rest for a long time because of your pain, your body can get more sensitive to movement because you haven’t had the same exposure to it. At this point, we’re sort of denying patients what we know is best practice care because of their own assumptions about their pain and how exercise might make that pain worse. But, through education, we can achieve the behavior changes we want; education is the gateway to doing what is necessary for recovery.”
In an annual survey of patients at Form Physiotherapy, Moen said that more than 80% of them stated that education about pain neurophysiology was a “pivotal” part of their recovery.
“We have a lot of people who come to us who don’t even know that pain education is a thing,” he said. “They just know they have chronic pain and they are primed to think it’s all about the injury. But when you see that 80% of your clients say education was a key part of their recovery, you realize the clinical benefits. You understand why it’s so important to establish, communicate, and then act on this knowledge to improve.”
Moseley agreed, and said the combination of education and movement has the power to “retrain” the nervous system in a way that can improve not only function but also pain.
“When you make that shift toward understanding that your pain system is overprotective and you can do things to retrain it, you will feel better,” he said. “Many people progress to a life less impacted by persistent pain.”
What does exercise do to the nervous system?
What might this “retraining” look like in the nervous system, with regard to exercise in particular? Michele Sterling, of the University of Queensland in Brisbane, Australia, and colleagues recently scoured the literature to find brain imaging studies that might show any marked changes in the brain after patients with chronic pain participated in an exercise program. That search yielded only four studies, but a lack of randomized study design, considered the gold standard in human research studies, in that small group of studies made it hard to draw any conclusions.
“We thought that, perhaps, the exercise would affect the areas in the brain commonly associated with pain, but there weren’t enough studies available for us to be able to show this,” she said. “We’d like to ultimately be able to look at the effects of different exercises on the brain so we can see what types or amounts of exercise might be most beneficial.”
Kathleen Sluka, a pain researcher at the University of Iowa in Iowa City, said that work in animal models provides some clues about the types of changes that exercise produces in the nervous system.
“There’s always this balance between the amount of excitation in the nervous system and immune system versus the amount of inhibition,” she said. “It turns out, in chronic pain conditions, we have a lot more excitation. The neurons become hyperexcitable and the immune system secretes more inflammatory cytokines [small proteins] leading to an inflammatory state. At the same time, we have less inhibition. But, with regular exercise, both the nervous system and immune system release different substances that bring back some of that inhibition to reduce all that excitability. If you exercise regularly, it will reset the nervous system and immune system, and, over time, shut down pain.”
That said, one of the biggest obstacles to pushing this reset button is that, while exercise decreases chronic pain in the long run, it can lead to increased pain in the short term.
“There are a lot of clinical trials looking at exercise for chronic pain, particularly musculoskeletal pain,” said Sluka. “There is an overwhelmingly positive response if it is done repetitively; it reduces pain and improves function. But we also know that people who have musculoskeletal pain have an acute increase in pain, especially when they start. We’ve done studies in fibromyalgia showing you can get a three-fold increase in pain during an active exercise task. That’s pretty big.” Helping people move past that initial acute increase in pain is tough, Sluka acknowledged. But she said education really is the key to getting started.
Romy Parker has found in her studies that it is especially the combination of education and exercise that really improves function and reduces pain.
“When you can educate people that pain doesn’t necessarily mean danger, that it’s not just about the tissue, you can help them get to where they will exercise,” Parker said. “The human body is a lot more resilient than most people give it credit for. In fact, the message most people receive is that the body is incredibly fragile. They are told their cartilage has worn away or the disc has slipped. But we now understand that the human body is incredible, and it can compensate when you build strength and do these exercises. So, when you can put the education and the exercises together, which lets them know just how adaptable the body is, you get much bigger effects for people.”
Sterling said there is still much to learn about the appropriate dose, duration, and intensity of exercise to help manage musculoskeletal pain. With regard to those questions, Parker said her work shows that the beneficial effects come about provided people do exercise that they actually like, which makes it much more likely that they’ll exercise regularly.
“Coming up with the right regimen is more of an art than a science, and it takes a lot of trust and communication between a physiotherapist and a patient,” according to Parker. “That said, our work suggests 20 minutes of exercise seems to be a pivotal point where your central nervous system kicks in and starts making some changes. We also have learned that you should work at an intensity where you can easily talk, but not sing. But, ultimately, what we see is that it doesn’t matter so much what you do, as long as you like it, because then you’ll keep doing it and then you’ll see the changes you want to see.”
Kayt Sukel is a freelance writer based outside Houston, Texas.