The evolution of muscle pain: does muscle “burn out”?

Muscle tissue is probably full of evolutionary compromises, just like the rest of biology. It has probably evolved to as high a level of function as possible in youth, at the price of a loss of healthy function as we age — which may be a plausible (if rather non-specific) explanation for why muscle pain becomes so common as we age, in the form of “muscle knots” (or trigger points, too many of which is known as myofascial pain syndrome). In short, we burn out.

All high-functioning systems — both evolved and engineered — usually walk a fine line between performance and blowing up, and typically fail with age. For instance, all flying machines tend to require intensive maintenance and are more or less constantly falling apart and being put back together. The SR-71 Blackbird fighter jet, the world’s fastest throughout its career, tolerated such extremes of heat at full speed that its parts needed room to expand, and so they were engineered to be loose-fitting on the ground, resulting in all kinds of challenges and risks, such as leaking expensive and explosive jet fuel like a sieve — by design!

Muscle is probably similarly volatile, not just full of compromises, but extreme ones — performing on a razor’s edge between performance and vulnerability, and with potentially significant consequences even to relatively minor deviations from operational norms.

As a simplistic example, with a strong shot of adrenalin, you can get super-strength out of muscles simply by recruiting every muscle fibre to contract simultaneously, instead of only a few at a time as with the relay system we normally use. Such great strength is possible only by paying a price of rapid muscular fatigue. Natural selection picked the balance point: if we were any stronger in general (via this mechanism), we’d get tired too fast and be food for big cats and such; any less strong, and we’d be so weak that we couldn’t run fast in the first place.

Never mind athletics or combat! Every day, your muscles have got to pull off miracles of fast, responsive, intense function in the course of performing quite ordinary actions. That function almost certainly comes with biochemical price tags. In a general way, this is probably why we get trigger points — they are glitches in an impressive but imperfect system, nonlethal and uncomfortable trade-offs for having muscle that is rather amazing in terms of performance. If I’m right, we should expect to see trigger points crop up (activate) at their operational extremes — and indeed we do. They tend to form in response to things like over-exertion, cold, injury, as well as anything that challenges the system as a whole like stress, sleep deprivation, and smoking. Systems fail and misbehave when challenged.

This evolutionary theory of trigger point formation is also somewhat consistent with the age of victims: children don’t suffer from trigger points anywhere near as much as adults. Myofascial pain syndrome seems to get rolling in the 20s, peaks in the 30s and 40s, and then levels off, not getting much worse in subsequent decades of life. Why don’t the young ‘uns get trigger points? Evolutionarily speaking, it would be a really bad idea if your muscles kacked out by your 20th birthday simply because of their own high-functioning! Not a good system! Nature would be hard on people born with that system, with the usual effect: more getting eaten, less breeding.

But past the age of 20? In the barbaric mists of history, your ability to survive into a third decade was largely a moot point, evolutionarily speaking: most everyone passed on their genes by that point (probably a few times), and you were worm food by 30. Evolution didn’t “see a need” for muscles that could perform miracles with no consequences for three decades. So we didn’t get them. And we never will. Broadly speaking, this is why aging sucks: once you are past breeding age, you are in biological territory that evolution can’t touch.