Des Moines University Clinic, Physical Therapy and Pain Science

How does pain work? Understanding the truth behind the hurt

When you take a second to think about it, pain is truly quite the concept to wrap your brain around. Why does my shoulder hurt? Why can’t I move my back? When will this go away? As a third year PT student, I hear these questions daily. The “why” behind the pain is amazing once you break it down.


How does your body process pain?

Pain is something nearly everyone will experience at least a time or two during their life. Whether it be from an injury, following a surgical procedure, or simply an insidious onset, pain can be a debilitating factor that plays a large role in our daily function.

A typical approach to pain management comes from a biological and anatomical standpoint. If there is dysfunction in a tissue, pain will exist. If you fix that anatomical issue, whether it be with surgery, injections, or exercise, the pain ceases to exist. Sounds simple, right? If only this were the case. Pain can persist even with no abnormalities in the tissue. Therefore, we must take a closer look at the biopsychosocial aspect of pain and dig deeper than just the superficial structures of the body.


The Mature Organism model

Taking a look at the Mature Organism Model proposed by Gifford in 1998 is a great first stride to step away from the typical biomedical model. The Mature Organism model looks at how the brain and nervous system receives input, processes, and outputs pain signals and what affect this has on the body.

Nociception vs. pain

Before we dive further into this model, I need to bring up an important point. Nociception is a hot topic when it comes to talking about pain. It is common to automatically assume that nociception and pain can be used interchangeably, but this isn’t the case. An important factor to remember is that nociception doesn’t always equal pain. Nociception is simply just an input that may elicit a variety of responses. Whether or not the body chooses to express this input as a painful stimulus is ultimately unrelated. This is why pain becomes so complicated. Two people with the same injury may perceive this in two very different ways. This could be because of a previous similar injury, fear avoidance, or the environment the injury occurred in. Now that we have this understanding of nociception, we can dive further into the model.

Pain input and correlated response

Breaking down this model piece by piece is the best way to understand how our brain works when it comes to pain. And to no surprise, input is the first factor. How we perceive something can make all the difference to how our brain decides to respond. In a heightened and intense situation, we are more likely to have a heightened and intense response. There is no difference when it comes to pain. C-fibers and A-delta fibers responsible for nociceptive pain input travel to the spinal cord to be processed by the brain. After an injury to tissue occurs these fibers are on high alert and relay hyper excitable messages that put our body in defense mode. This hyper-excitability increases when we are put into an environment that has great significance or great stake. Another notable factor when looking at input is the duration of this hyper-excitability state. In normal healing, the fibers delivering signals to the brain start to down regulate as things return to normal, however if the injury and pain persists, the fibers will continue to remain in the hyper-excitable state and can cause continual and even worsening pain perception. For example, if someone has shoulder pain due to a rotator cuff tear for 2 years, the pain may persist even after getting surgery and rehab for that injury simply because of the duration that body was consistently receiving those inputs for pain.

Processing pain

Processing is the next step in the Mature Organism Model, and we have already touched briefly on this topic. The brain processes nociceptive pain input mainly through C-fibers. When these inputs are consistent, dysfunction in the spinal cord, brainstem and cerebral hemispheres can occur. This dysfunction can occur even after things have healed on an anatomical level. The persistent input increases sensitivity over time and often leads to more widespread and global pain from where the injury occurred. For example, someone has a shoulder injury and has pinpoint tenderness through the joint. The injury to the shoulder continues to heal but the input and processing through the nociceptive fibers remains and intensifies. The patient now complains of tenderness through not only the joint, but also the shoulder blade, into the biceps tendon and through the cervical spine. Not only can time be a factor for processing, but simple belief and perception of pain also play a large role. For example, if you look at someone injured in a motor vehicle accident vs. a football player, those two people are going to experience pain quite differently. Just based on the experience and settings they are in, they are going to see and respond to injuries in different ways.

The football player gets excitement and endorphins while performing his sport, which involves having repeated blows to his body. This athlete tends to associate this pain with winning or adrenaline and typically has a positive experience when it comes to this repetitive trauma. On the other hand, someone who is not used to this consistent trauma and has had just one major accident tends to associate that pain with anxiety and fear that something may happen again while driving. These two people may have similar injuries but due to their perception and belief about the pain, their experience and processing of that pain will be output in two completely different ways.

Pain output

Lastly, we have output. Bringing this model full circle, it’s important to touch base on how the body responds when it’s heightened response to pain remains constant over a long period of time. Unfortunately, the body is not made to sustain constant levels of hypersensitivity and other systems must compromise to deal with this. Blood flow decreases to musculature, cortisol levels rise, nerve sensitivity continues to rise, muscle atrophy sets in, and even general mood can decrease. Therefore it is so important to address not only what is going on with the physical aspect of pain, but also the psychosocial aspects and the environment.


Does physical therapy help relieve pain?

Now you may be wondering how physical therapists can help with all of this, and in fact we can make a bigger difference than you may think! As physical therapists, we spend quite a bit of time on the psychosocial aspect of treating our patients. Some of the sessions we have with patients are simply just talking and retraining the brain with how they may think about their injury or pain. We believe that the body needs to be treated holistically and we cannot neglect the brain with our treatment. There is no doubt that manual therapy skills and therapeutic exercise have their place in healing: creating rapport with patients, providing education on how the brain and body function and working to down regulate the stress and anxiety that plays into pain can be just as effective. These strategies for the treatment of pain are proven in the literature to be effective for long term pain management and you have the control within yourself to understand why you hurt and to return to living your best life!  


Need help recovering from an injury? Our exceptional physical therapists at the Des Moines University Clinic can help. We are currently offering in-clinic and virtual appointments for patients. Visit the DMU Clinic website or call 515-271-1717 to learn more.

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Taylor Joens

Taylor Joens is a 3rd year physical therapy student born and raised in Des Moines. She enjoys playing intramural volleyball with her classmates, getting outside to bike or hike, and spending time with family and friends. Taylor hopes to practice in the Kansas City, Missouri area after graduation and treat a variety of patients throughout her career.

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