To understand low back pain, researchers are looking closely at how our bodies move

Anyone who suffers from chronic low back pain knows how difficult it can be to manage, and how quickly it can turn the most ordinary activity into a daunting prospect. Nonspecific and difficult to pinpoint anatomically, its root causes often elude treatment and can result in a strikingly broad range of impairments. 

That’s partly what makes back pain the number one health care-related expenditure in the U.S., according to a study published in the Journal of Orthopaedic Translation. And despite being one of the most common causes of disability in the world, surprisingly little progress has been made in developing effective treatments. 

Researchers at UC Berkeley and UC San Francisco are addressing the condition with comeBACK, a study that aims to make advances in personalized treatment for those who suffer from it. The team’s first step? Exploring the connections between chronic pain and movement, and in particular, how these experiences vary between men and women. 

The study’s findings, published in the European Spine Journal earlier this month, reveal an unexpected conclusion: Though males are less sensitive to low back pain than their female counterparts, they also exhibit a reduced quality of movement and a greater aversion to activity. Using full-body motion capture and pressure pain threshold tests, which measure the minimum pressure at which pain is felt, scientists were able to expand our understanding of how the sexes experience the condition.

UC Berkeley News spoke with two of the study’s co-authors — Grace O’Connell, a Berkeley professor of mechanical engineering, and Jeannie Bailey, professor of orthopedic surgery at UCSF — to learn how a better understanding of sex-based differences might lead to more effective treatments for chronic low back pain. 

Your study points to chronic low back pain as the leading cause of global disability and minimal treatment outcome improvements in the past 30 years. Why is chronic low back pain so challenging to treat effectively?

Jeannie Bailey: With chronic low back pain, in general, it’s hard to know what the underlying cause is. Sometimes there’s no obvious indicator from imaging, like an MRI, so you don’t know what’s causing the pain. And when you don’t know what’s causing the pain, you don’t know how to treat it. Often surgery is not an option because, in that case, what would you operate on? So there’s physical therapy and other sorts of pain treatments like epidurals and steroidal shots. Because it’s hard to treat, because there’s chronic pain, opioids tend to be relied on, and they’re dangerous. 

O’Connell: As we get older, our tissues degenerate, our spine degenerates, and so as Jeannie mentioned, you can have MRIs of people, and they’re degenerating, but that doesn’t really tell you if that’s what’s causing the pain, which makes treatment a lot harder. And then if you do get surgery, it may not treat the pain long term, and the patient may be at risk of having a mechanical failure from that surgery. All of these things factor into the complications of treatment. 

You hypothesized that lower levels of pain sensitivity in males with chronic low back pain would correlate with superior biomechanical function. Did that turn out to be true? 

Bailey: We actually showed that lower pain sensitivity in males correlated with worse biomechanical function. What we found is that males are less sensitive to pain, and they move worse, because they’re less reactive. Our conclusion is that females sense pain quicker, and that’s why they’re moving better than males who have back pain.

Why think about sex-specific mechanisms? Why is that important in considering the relation between pain and movement? 

Bailey: We knew that there’s sex differences in pain. So we were curious if that related to perceived pain: Do women report having higher maximum pain? We didn’t see that, but we see they are more sensitive when we do the actual testing. They’re reporting a similar level of pain, but that’s [their] perceived experience. I think what led us here is seeing the really obvious difference in motion and trying to figure out why the movement differences were present. 

O’Connell: I also think there’s been a push to look at sex as a variable. Since 2016, the National Institutes of Health started saying you have to look at it, so even when you wouldn’t think there would be any sex-based difference, … big surprise! There are differences in places where you might not expect. I think there’s just been a shift in the culture in the scientific community. 

You alluded to a possible difference between total pain and pain sensitivity. Can you elaborate on that?

Bailey: Say you have back pain, and you go see your doctor, and they ask you on a scale of zero to 10, “How severe is your pain?” How do you know how to answer that question? The way that we measured the thresholds for pain was based on this indentation for sensitivity testing, which is something that people have a little less control over. it might be a little more physiological than your perceived pain — your perception of pain versus how it’s actually affecting you. 

Taking into account individual pain sensitivity, is it possible that other factors like socialized gender norms could account for the sex-based differences?

Bailey: I think so. I really think the lack of sex-based differences we saw in the perceived pain is potentially a factor of gender norms, of women just underreporting how bad things are or how they’re experiencing them. I think women are adapted to be more used to pain because of evolution.

What do the study’s findings portend for the future of pain and body movement research? Are we nearer to a breakthrough in developing effective treatments for chronic low back pain?

Bailey: I think that we’re getting somewhere with phenotyping patients to understand different types of chronic low back pain and how they actually create impairment or not. Better understanding the heterogeneous population of chronic low back pain patients will probably help us inform treatment selections that will work better. How do different pain mechanisms relate to biomechanical impairment? Understanding how the pain informs dysfunction, we start understanding the condition better. And then once we know if it’s creating dysfunction or not, what is the right treatment avenue? Is it physical therapy, or is it more biopsychosocial?

There are so many ways to treat chronic pain. Opioids are obviously a pharmaceutical for it, but there’s also mindfulness and cognitive behavioral therapy. You can imagine that for a person who has chronic pain but is moving just fine, you’d probably go down those routes. But when a patient is moving horribly, you’d probably need to have physical therapy and learn how to move better and cope with the pain. So you can see how understanding how these things are impairing their lives and affecting them informs the treatment selection.

The interview was condensed and edited for clarity.