Navigating the Pain Trail – Tissue Sensitivity, Defusing the Threat
Back again for more pain! Here’s a quick primer on what we discussed in our first article on running pain:
- Pain is information. Specifically, it is any information the brain (or “Board of Directors”) deems threatening. It should be neither feared nor ignored.
- Pain is a brain output based on sensory inputs, not only from peripheral nerves, but all of our senses.
- Pain correlates poorly to actual tissue damage.
In this article, we’ll expand on those concepts to address chronic pain and how it develops and persists, in spite of our best efforts.
The Board of Directors, Revisited
Last article we discussed the concept of “The Board of Directors” or the accumulation of various parts of the brain that accumulates and interprets all sensory information. It uses previous experience and personal values to make decisions: “Sticks don’t hurt. Snake bites do.” Or, “Quad soreness doesn’t hurt, but low back pain does.”
Based on that threat assessment, the Board makes decisions and takes action, both conscious and unconscious, to protect us.
But what happens when that information is no longer credible? Or if the Board becomes overly cautious?
Pain Management and Central Sensitization
Physiologists and researchers in pain describe chronic pain as the result of central sensitization: the notion that the central nervous system becomes overly sensitive to information.
When tissue damage occurs, various sensations are registered: tissue strains cause leakage of intracellular chemicals onto nerves. This signals chemical, pressure, and temperature receptors to send information to the brain. This registers (usually) as pain.
Pain management concepts – e.g., a “RICE” approach of Rest, Ice, Compression, Elevation – when appropriately applied, invariably results in healing. Different tissues have varying but well-established healing times:
- Soft-tissue inflammation (muscle, skin, minor tendon strains): 10-21 days
- Bone fracture and moderate tendon strains: 4-6 weeks
- Cartilage, major tendon or muscle strains (ruptures) and surgical repairs: 2-6 months
So how is it, then, that many injuries – despite several months if not years of healing time and copious rest – still cause severe pain?
When tissue healing is poorly managed, or when threat value is high, the brain continues to produce pain. Inputs and interpretations cause the Board to decide, “Hey! We need to pay attention to this!” When this situation persists for weeks (or for some, months and years), real physiological changes occur to the information system that keep us in pain, and often make it worse:
1. Nerve tissues become more sensitive to information
With prolonged pain outputs, the Board determines that, “The information from Left Leg is constantly worrisome. We need to keep tabs on this situation! Rather than getting five reports a day, let’s get ten.”
Based on that response, the central and peripheral nerve will generate a greater number of nerve receptors. Receptors are cellular structures that, when activated, will trip a nerve to fire. Nerves have different kinds of receptors that will respond to:
- Light Touch
- Stress and Anxiety!
Chronic, prolonged pain will cause a greater number of receptors and make them easier to trip. Moreover, current research demonstrates that stress and anxiety are the primary receptor types that “grow” on nerves in states of chronic pain. For a runner trying to overcome injury, this may mean that their foot or back pain may occur at one mile, instead of two. Or one meter. But there is no actual tissue damage; rather, the nerve is now more sensitive.
2. The brain becomes more receptive to information
While the peripheral nerves are becoming more sensitive, changes occur in the spinal cord as well! The peripheral and central nerves meet at a junction in the spinal cord (for legs, in the low back, for arms, in the neck). At this junction, there are several “interneurons” that serve to relay information. One cell, in particular, serves as mediator of information. He takes a look at all the reports coming from the legs and helps decide what’s worth letting in, and what can be ignored. He’s “The Bouncer.”
In chronic pain, the Board will determine that it needs all the information it can get, and it will deactivate (and, based on some research, actually destroy) “The Bouncer,” which allows a free flow of any and all stimuli from the body to flow into the brain.
Therefore, this series of events creates a situation where “x” amount of tissue input is interpreted as “10x” or “100x” by the brain. Reality is skewed. The slightest amount of running, walking, or even active or passive joint motion is painful.
Signs and Symptoms of Central Sensitization:
- Symptoms persist beyond normal healing times (>3 weeks to >3 months or more)
- Symptom area “grows outward” from original (more pinpoint) injury area
- Symptoms change, from ache/soreness to stabbing, buzzing, “lightning bolts,” tingling
- Symptoms occur at rest, or without weight bearing
- Symptoms worsen at times of stress and anxiety
- Tissue tolerance (sitting, standing, walking, running) actually worsens…
Sensitization is important in primitive survival: tissue damage is a threat that requires acute monitoring to avoid. But when these changes occur in the absence of any tissue damage, the pain – and the threat of that pain itself – is the sustaining element of the pain cycle:
Tissue damage → threat → pain → sensitized tissue → more pain → more threat → more pain…
Understanding this system is vital to overcoming chronic pain. The realization of, “What I’m feeling right now might not actually be tissue damage… I might just be sensitive!” is critical in taking steps to overcome chronic pain. Moreover, recognizing how our attitudes, beliefs, and stress/anxiety affect pain is vitally important.
This gets us back to the question: “If pain is information, what is mine telling me?”
Based on what we now know, the answer might be one – or all – of three things:
- I need rest!
- I need more load!
- This information is erroneous!
More or Less? Inflammatory versus Ischemic Pain
When tissue damage occurs, it is invariably an inflammatory condition: inflammatory chemical rush to the injury site, the area swells and becomes warm, cells begin to repair. And, usually, it hurts! In acute and sub-acute inflammation (10 days to three months, depending on the tissue), rest is critical for tissues to heal.
When pain persists beyond scientifically-accepted tissue healing times, then rest is seldom the answer. Pain in response to tissue loading might be telling you, “Yikes! That’s stiff! Keep working me!” In those situations, pain is likely ischemic – or due to lack of blood and fluid flow, and overall mobility. Ischemic tissue needs the opposite of inflammation: active and passive motion, blood and fluid flow, and progressive tissue loading.
Think of the different tissue types as meat. Inflammatory tissue is like a medium-rare steak: fresh, warm, soft, fluid-filled, flexible. Hot off the grill, it needs to sit a bit, and cool off. Ischemic tissue is like beef jerky: aged, dry, tough, dysfunctional. To become pliable, it needs heat, fluid, and mobility.
So how do you know what kind of pain you’ve got? Your doctor, PT, or other health care professional can help you determine whether your tissue is inflammatory versus ischemic, but here is a relative comparison:
|Age of Injury||<3 months, usually <3 wk||> 3 weeks or older|
|Peak Symptoms||End of the day||Middle of the night, first in the AM|
|Symptoms||Ache, throb, stab that lingers||Sharpness, immediately subsides w/rest|
|Treatment Approach||R.I.C.E.||Flexibility, relaxed mobility, progressive loading|
(*adapted from lecture notes, “Explain Pain”, NeuroOrthopedic Institute, Adriaan Louw, Minneapolis, MN, November 2012)
Escaping the Pain Vortex – Building Tissue Tolerance and “Defusing the Threat”
Freeing oneself of pain – inflammatory, ischemic, and hypersensitivity – requires progressive, patient loading of tissue. Despite where the symptoms come from, they must be respected.
Muscles, bones and joints – while clinically healed – might still be unfit or disorganized. Thrashed quads, weeks after a hard 100-miler, might be fully healed but still dysfunctional and tough, like the beef jerky. A fully healed plantar fascia might only tolerate a full day on your feet, and nothing more. Progressive tissue loading is required to gradually restore the tissue to desired function.
For runners, building tissue tolerance should be a familiar concept: it’s training! We all know that just because we could run four-hour long runs six months ago, doesn’t mean we can automatically do so, today. Even when healthy, we lose tolerance when we rest. It must be gradually rebuilt.
Injured tissue is no different. It requires gradual building-up of load over a prolonged period of time to strengthen and toughen.
The system that most needs gradual loading is the nervous system. The Board of Directors, after months and years of pain, is, indeed, “nervous.” And just because pain perception might be due to erroneous information, doesn’t mean the pain response is fake. It is, indeed, real, and must be respected.
Thus, to desensitize the nervous system is paramount: to progressively load tissue, just enough to convince the systems that it is “okay” and “Sore but Safe”, to defuse The Threat.
People who can accomplish this feat – progressive tissue loading, desensitization and threat defusing – may do so quickly, and will often report “miraculous” cures, because they finally give their tissues what they need: blood flow, flexibility, and relaxed, confident function!
Tissue Tolerance and Desensitization: A Case Study
I’ve experienced this “miracle” firsthand:
Before my first Western States 100 in 2011, I experienced a knee injury. I strained it in early April, yet by the end of May (nearly two months), severe pain persisted: it hurt with the slightest movement, walking was painful, biking was intolerable, running was out of the question.
Threat value was sky-high: I was running my first hundred, I was unprepared, I had a dozen friends and family committed to helping. Moreover, I was mentally catastrophizing: “If I cannot walk without pain, how could I possibly run a hundred miles?”
At the end of May, critical things occurred:
1. I determined that there was no severe tissue damage.
A simple x-ray ruled out any bony pathology. The absence of swelling ruled out ligament or cartilage pathology, and it confirmed that tissues were healed.
2. I recognized how my own attitudes, stress, and anxiety impacted my pain.
Stress, anxiety, and threat caused two things: abnormal (protective) movement patterns – not letting it relax and bend normally, as well as increased muscle tension and decreased blood flow to the area. The knee tissue was ischemic, not inflammatory.
3. I began to progressively load and defuse threat.
Recognizing the physiological reality, the impact of my mental state on the tissue function, and rationalizing that I’m “Sore but Safe,” I began to gradually load the tissue.
Starting Memorial Day Weekend:
- Pre-Friday: Zero running for over a month.
- Friday: 35 minutes of running, one minute on, one off. I was “Sore but Safe” – pain during the run, but none immediately after. I was relaxed and positive about the progress.
- Saturday: Walked from Michigan Bluff to a mile past Last Chance… then ran back nearly the entire way (26 miles, total – 13 of it running). “Sore but Safe!” More excited…
- Sunday: Ran from Michigan Bluff to Rucky Chucky, 23 miles, total.
What a miracle, right? Or did I finally give my knee exactly what it needed? Relaxed, normal motion, and progressive (albeit, aggressive) loading. I was sore as heck after that weekend – general muscle soreness everywhere – but I had no knee pain. Race day was similar: loads of body pain, a safe knee, but most importantly, a Silver Buckle.
Recognizing what pain is telling you is like learning a new but important language. You need not be fluent, but simply gaining understanding of the impact of our brain and nerves on pain and injury will help defuse the threat, and get you back on the trail!
Call for Comments
- Have you experienced Central Sensitization firsthand? An injury that took far longer to heal, that created abnormal, hyper-sensitive symptoms? How did you “escape”?
- Describe your experience with “miracle cures.” What happened, how did you emerge, and how might that relate to sensitivity and tissue loading?
Explain Pain, Butler & Moseley. Orthopedic Physical Therapy Products; 1st Ed. (2003)