Aches and Pains

We do not mean to preach against the very important role of nociception in pain, nor the very important role of potential or actual tissue damage in both nociception and pain. [… However], to engage with the biology of pain is to let go of the erroneous notion that pain is a measure of nociception and that nociception is a measure of tissue damage. Even in highly controlled experiments the notion of tissue damage = nociception = pain does not apply.

– Lorimer Mosely & David Butler 

Pain is not a measure of nociception and nociception is not a measure of tissue damage. The relationship between injury, nociception, and pain is complicated.

If a load (external force) is applied to bones, muscles, ligaments, etc., they undergo stress and can strain (change in shape, length, width).

Types-of-force-255x300

An injury occurs when a tissue can no longer support a load and “fails.” This happens when the plastic range is exceeded. In living tissue, these ‘permanent’ changes can sometimes be reversed.¹

stress strain

Injuries go through a process of healing. While different tissues take different times to heal, healing is a predictable process. All tissues go through a inflammation, proliferation, and remodeling phase. These phases aren’t discrete and overlap.

 

Additionally, it’s important to note that pain often goes away before an injury is even healed.

Nociceptors are free nerve endings. It’s useful to think of them as “danger” receptors. They are high threshold receptors that detect temperature, pressure, and chemical stimuli.

Nociception is a purely physiological process. It refers to a mechanism in the nervous system whether or not there is pain. It DOES NOT imply pain perception. No matter how much we know about the details of a nociceptive mechanism, we can’t know how much that mechanism influences individual’s overall and subjective pain perception (though it most likely will).²

nociceptive system 2

Pain often has a variable relationship with injury. It’s intuitive to think that tissues without pathology aren’t painful and tissues that have pathology are painful.

fig 1

This is inaccurate. Most commonly, it’s because people have some sort of pathology without pain. Most of us would have some sort of tissue “issue” on our MRIs, even without any symptoms of pain or “stiffness.”

fig 2

However, it can also be because people with pain do not exhibit any pathology outside of normal. It’s also important to realize that nociception occurs all the time whether or not we are experiencing pain.

Lars Avemarie says it best:

“Recent research has shown us that you actually can have pain in the body without anything being wrong in the area of that pain. You can also have “damage” and so called degenerative changes in the body without any pain. As I see it, there are four possibilities:  Having tissue damage and pain. Having no tissue damage and no pain. Having pain but no tissue damage. Having tissue damage but no pain.”

This is because pain is an entirely subjective experience. It is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in such damage.³ Without psychological awareness pain cannot exist. There isn’t an objective way to measure it and it’s very hard to express.²

the-scream

The assumption that pain is linked with tissue damage is protective, reflexive, and ingrained biologically, psychologically, and socially in human nature. It is this a very strongly held and deeply embedded assumption, which is difficult to break when pain persists in the absence of treatable tissue pathology.