Does Chronic Pain arise from an evolutionary mismatch?
Chronic musculoskeletal pain is one of the big elephants in the room in Western Society. It’s far more prevalent than we realise, and impacts the wellbeing and participation of millions of people worldwide.
Most of the research in the area tells us that when pain persists, it does so because of reasons beyond injured or damaged tissue (Think biopsychosocial model). In fact Injured or damaged tissue may play less of a role as pain persists than many of us might expect. So we’re left to ask ourselves two main questions:
How did this problem get so big and complicated?
Can we heal/resolve chronic pain? or do we just better manage it?
Leaving aside the enormous second question. I feel the above mentioned paper from Büchel set out some compelling arguments for why chronic pain might be more prevalent in our current evolutionary context.
He states: “technological and societal changes have accelerated rapidly, dramatically changing the human environment. By contrast, evolution with the mechanism of selection over generations is rather a slow process in organisms with a long generation time and has difficulties to keep pace with fast environmental and societal changes. It is thus conceivable that many biological processes in humans are not fully adapted to the challenges of current environments.”
A mismatch has arisen, he says, between our current environment and the one that we best evolved to exist in.
You see, an interesting thing about human beings is that we actually have our own internal drug cabinet of pain relief mechanisms. These are broadly categorised under the ‘descending pain modulatory system’. This system allows the inhibition of pain by modulating neuronal activity at various stages of the central nervous system from the spinal cord to the cerebral cortex.
In simple terms - this system activates to reduce pain when we are made to move or act, or given a meaningful enough action to complete. There is all kinds of research showing people helping in others in emergencies despite their own serious injuries, or reduced pain from induced placebo effects in experimental and clinical contexts. This is thought to be largely due to the functioning of the descending pain modulatory system (DPMS).
In our recent evolutionary past, someone who was injured would have likely been compelled to move due to survival pressures. Whether that be the avoidance of predators, fellow humans or seeking out food and shelter. This would have led to activation of the DPMS, reducing the persons symptoms enough to allow them to move as required. But these days, someone who is acutely injured or in pain doesn’t have these same pressures. They are allowed to rest and recover (rightly so), and not given the onus to move or act unless they decide to, or have to.
But what if this actually interrupts or prevents the normal healing and recovery process? What if we are required to move to optimally heal?
Similar to the problem of obesity arising in part because of the ease of accessible high-caloric foods, this pleasant privilege of resting and recovering as much as we like, may actually lead to us recovering slower or not at all. Thus contributing to the large prevalence of chronic pain we see around us today.
We know now that exercising through pain in acute hamstring injury, leads to at least equal if not faster recovery times. And exercising through chronic pain in general leads to slightly better short term outcomes
Büchel argues that there is emerging evidence to suggest improved recovery time/resolution associated with activation of the DPMS in various chronic pain conditions and even after some surgeries.
At the end of the day, persistent or chronic pain is an emergent, complex and multifaceted problem that does not have one singular fix or cure. It requires creative, complex emergent thinking to address and potentially overcome. But as the great David Butler said - “motion is lotion”, and “rest is rust”. Whilst we may require some rest and inactivity to allow the early stages of repair and recovery to occur. We ultimately have to get moving as soon as we can, however we can, to get better.
References
1. Büchel, C. (2022). Pain persistence and the pain modulatory system: an evolutionary mismatch perspective. Pain, 163(7), 1274-1276.
2. de C Williams, A. C. (2016). What can evolutionary theory tell us about chronic pain?. Pain, 157(4), 788-790.