Do we move differently in pain?
For the past few years, my studies in pelvic health have taken me further and further outside of the pelvis. I have learned and continue to learn how amazingly interconnected our bodies actually are. The pelvis can be influenced by the ankle, the knees—and even the neck! It is amazing and awe-inspiring. This past weekend, my studies took me to the Level 1 Selective Functional Movement Assessment (SFMA), where I spent 2 days learning a systematic way to evaluate movement and identify where dysfunctional patterns exist—head to toe! (How awesome is that?!) There are many different systems and programs out there for evaluating someone’s movement, and honestly, I don’t necessarily think one is superior to the other. I liked this one though, as it made sense to me and the initial screen could be completed in 2 minutes :).
So, why is it important to look globally at human movement when a person is experiencing pain anywhere in the body? For lots of reasons, like I said above—but for the purpose of today’s post—because we now know that movement patterns do really change when a person is experiencing pain—and this is helpful initially and important—remember, your brain wants to protect you from experiencing harm! However, dysfunctional movement patterns, although helpful to the body in that moment, can persist and lead to further problems down the road.
Paul Hodges (a favorite researcher of mine!) and Kylie Tucker examined the current theories regarding movement adaptations to pain in a 2011 review published in the International Association for the Study of Pain. They looked at the current research regarding movement variations in pain, and frankly poked holes in the theories where holes needed poking. They then presented a new theory on the motor adaptations to pain, and that’s what I would like to share with you today.
The theory they presented is based on the premise that movement adaptations occur to reduce pain and protect the painful part. The way in which a person does that actually varies and is flexible. Here are the basics of their theory, simplified, of course. I do encourage you to read the paper if you’re interested—it’s great!
Adaptation to pain involves redistribution of activity within and between muscles. Basically, the brain varies which pools of motoneurons fire in a muscle based on the individual and the task requirement. The common goal still is to protect the painful part from pain or injury, but the way the body does this can vary greatly. Interestingly, we know that the motoneurons active before and during pain tend to reduce activity, and the production of force actually seems to be maintained by a new population of units who were previously inactive. Normally, motoneuron units are recruited from smaller to larger pools to allow for a gradual increase in force—but in pain, a person often will have earlier recruitment of larger pools to basically allow for a faster development of force to get away from pain (think fight or flight response!). Also, the new population of active units may be altered to change the direction of the force generated by the muscle (again, aiming to help protect the painful structure). We also can see in some areas, like the trunk, that one muscle may become inhibited (like the transverse abdominis) while other larger muscles become more activated. This again, makes sense with the body’s goal of protection. Quick activation of larger motor units allows for a quick activation of a muscle to help protect and escape pain.
Adaptation to pain changes mechanical behavior. Basically, like we just discussed, the redistribution of activity within and between muscles changes the force and output of the muscle. Hodges & Tucker give us a few examples of this. First, they’ve found that when someone has knee pain, the quadriceps muscles fire differently to change the direction of knee extension by a few degrees. They also explain that the changes in muscle firing in the trunk muscles in someone with back pain leads to more stiffness and less control of movements and less anticipatory action. Basically, in each of these cases, the big picture motion stays the same, but there are small changes within how the body accomplishes those tasks.
Adaptation to pain leads to protection from pain or injury, or threatened pain or injury. Basically, this redistribution of muscle firing is done to protect against pain—or even the threat of pain. When a person experiences pain, the brain choses a new pattern to move to either splint the injured area, reduce the movement of the area, or alter the force on the area. The interesting piece here is that the body responds this way even when there is a perceived threat of pain! The key with all of this is that the adaptation varies significantly—not one pattern is seen for all types of pain, but the nervous system has a variety of options for protection!
Adaptation to pain involves changes at multiple levels of the motor system. So, although we know that the activation of motoneuron pools can change during pain, that alone does not describe the variability we see. We know now that the way the body changes movement can be influenced by structures in the brain, spinal cord or at the local level of the motoneuron. All of this is going to be influenced by the task at hand and the individual (thoughts about the pain, emotions, stressors, and previous experiences)
Adaptation to pain has short-term benefit, but with potential long-term consequences. Although the short-term benefit is protection of the painful area and prevention of further pain, this may lead to consequences down the road if the adaptation persists. Of course, we assume in this case that movement in a non-pain state is likely the most efficient and optimal way to move. So, changes over time could produce decreased movement variability, modified joint loading, modifications in walking patterns, joint load and ligamentous stress. Hodges and Tucker state that in order for these long-term consequences to occur, there would likely need to be a gradual maintaining of the compensation, thus that the nervous system did not recognize it being problematic. Basically, the brain slowly adapts to the new pattern and does not recognize the problems it could cause down the road.
Interesting stuff right? The tricky thing is, we don’t really know for certain how these long-term changes can impact the body—but we do know that one of the biggest risks for injury is previous injury. I can’t help but think that movement changes could possibly contribute. But how do we change this in a positive way? I think the first step is understanding pain, learning what pain is and what pain is, and developing a healthy mindset toward pain—this alone goes a long way! We also have to look closely at our own emotions, our psychological state, our previous experiences, and understand how all of these things can influence how are brain chooses to respond to pain. But then, we need to identify which movements the body has changed, understand how the brain is varying movements to protect against pain, and then slowly provide variability with good force modulation in those movements to help the brain learn optimal, safe and pain-free ways to move again.
What do you think? I’d love to hear from you in the comments below!
Cheers!
Jessica