During the past twenty years, research on chronic pain has significantly increased, with advances in understanding its etiology, assessment, and treatment (Johannes et al. 2010). These discoveries have important healthcare implications as pain is the leading cause for why people seek out medical care, even more so for manual therapy. Whether or not pain relief is your immediate goal, the fact remains that the majority of people who walk into your office experience some degree of pain; as such, we must understand what pain is and most importantly what pain is not. It is no less important than knowing the anatomy of the body. This article is a review of the most recent understanding of pain, providing a summary of some of the latest pain science research that is both relevant and applicable to you and your clients. It proposes explanations for phenomena where, with your treatment, a clients’ pain may decrease, remain the same, or perhaps gets worse. Most importantly, understanding this phenomena is empowering for both you and your clients.
Client expectations and fears play important roles in the outcomes—positive and negative—of manual therapy. These expectations of treatment outcomes mainly include pain relief, improved function, and improved overall well-being—including mental well-being. That being said, having a good understanding of the neurobiology of pain will help practitioners meet their clients’ personal goals for seeking out care.
Within roughly the last twenty years, neuroscience and pain science have disproven the belief that pain exists solely in the physical tissues, a purely biomechanical explanation for pain (Gifford 1998, Lederman 2010). It is a major falsification of what we once believed. The International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Simply put, pain is the brain’s perception of tissue damage (Butler & Moseley 2003). Perception is key, because pain is about how a person consciously and non-consciously creates meaning of his/her physical reality. When the perception of our tissue state is less accurate, as with chronic pain, the perception has become an illusion. This perception of tissue damage (i.e. pain) is modulated by a number of cognitive, emotional, and sensory inputs (Carlino et al. 2014; Gifford 1998).
When someone in pain walks into your office, they want answers to the following:
1. What’s wrong with me?
2. How long is this going to last?
3. Is there anything I (the client) can do about it?
4. Is there anything you (the practitioner) can do about it?
(Verbeek et al. 2004; Gifford 2013)
When considering these questions, they make sense in terms of survival. However, if these questions are left unanswered, we begin to worry about potential disability in the future. When experiencing physical pain we sensibly, but mistakenly, place all of our attention in the physical domain. This leads us to conclude that pain is entirely a reflection of the state of our tissues, assuming the biomechanical model for explaining pain: poor mechanics = pain. Today, we see that this conclusion is falsified.
One of the brain’s chief priorities is to keep us safe and protected. Pain warns us of danger and compels us to take action to relieve and/or avoid that danger. Thus, the experience of pain is based on a prediction of danger we are physically in, not how much we really are in. Our response to pain results in altering the way we sit, stand, and move. Even if there are no problems in the tissues, nerves, or immune system, you can still hurt if your brain thinks that you’re in danger (Butler & Moseley 2003).
One class of sensory receptors called nociceptors were once, incorrectly, referred to as pain receptors. Nociceptors are receptors that require higher thresholds of stimuli to trigger an action potential, which in turn sends larger, more amplified signals to the central nervous system (CNS). These larger signals serve to get a person’s attention by acting as warning signals. The brain, though, can ignore input from the body, large or small, if the brain is either distracted enough or does not value the incoming messages. Pain is context-dependent. A notable example of this is seen with soldiers in the heat of battle who are shot but don’t feel pain until much later, once they are out of the dangerous environment.
Nociception is quantitative, not qualitative. This means the body’s sensory system simply provides raw data to an individual’s CNS. It is the brain which must then interpret that data’s meaning. While nociception is not an essential part of one’s pain experience, it can be a very powerful contributor.
One of the most important factors in understanding pain is injury healing times and their relevancy. Wound healing is a complex and dynamic process consisting of four phases: hemostasis, inflammation, proliferation, and remodeling. Typically, most tissues heal within 1-6 months. Soft tissue, such as skin, takes around 10 days to 2 weeks. Deeper soft tissue can take 3-6 months, and depending on the type of deeper tissue, it may take up to a year to regain full tensile strength. Bone takes up to 3-6 months to heal and up to a year to fully remodel (Maxson et al. 2012). Pain is mostly experienced during the inflammatory phase of the healing cycle, where a flood of chemicals excite the nervous system and lead to pain; glutamate, aspartate, substance P, adrenaline, cortisol, and cholecystokinin. Pain serves an important role during healing to ensure the process is preserved, and to prevent further tissue damage in order to facilitate a full recovery (Lederman 2015; Figure 1). Regardless whether the discontinuity of tissues remain permanent, as sometimes in the case of section tissues, the phases of healing eventually end. Recovery is partly a resolution of inflammation and attenuation of nociceptive excitation. When tissues aren’t able to complete this phase it’s do to the absent of metabolic energy i.e., blood, whereas surgery may be needed.