The trouble with demonizing trivial physical stresses

In 2018, Yamato et al. reviewed the effect of backpacks on back pain in kids as reported in 69 studies, including five higher quality long-term studies, and they detected bupkis:

The volume of research and the fact that associations show no consistent pattern suggest that any relationship between backpack use and back pain is minimal at best, and research resources aimed at understanding adolescent back pain are better directed elsewhere.

(One tiny signal they did detect: “the perception of heaviness is associated with back pain.” In other words, when you do have back pain, your bag seems heavier! Which does not seem surprising.)

The concern about packs is the old school version of the trendier anxiety about “text neck” — just with backs and backpacks instead of necks and smartphones. All of the research on this fails to show that minor physical stresses are harmful to spines (see Richards, Damasceno).

Hopefully evidence like this can undermine overconfidence in the importance of trivial physical stresses, posture, and biomechanics in back pain. Let’s put more emphasis on the psychosocial factors and subtler biological vulnerabilities that spinal pain is more sensitive to.

More examples and implications…

The physical strains we overestimate: three more examples

It sure can seem like “common sense” that physical stresses must cause back pain. For instance:

• It might seem like obesity must surely be responsible for the epidemic of back pain. And yet it clearly isn’t. Hussain et al found a clear link, but not for the reason everyone assumes, and Dario et al found no link at all, despite looking extremely carefully.

• Someone told me — doubting the findings of the backpack study — that awkward lifting technique “has to be” responsible for a lot of back pain. Not necessarily. We all have to beware of overconfident talk like “has to be” when it comes to the causes of chronic pain, because there are a lot of very non-obvious factors. It rarely works out to assign most of the blame to any one thing.

• Excessive sitting “has to be” a risk factor for back pain, right? Surely that? Probably not that either, no. I had to correct my own common-sense-based opinion on this topic several years ago when I realized that many studies have shown that people who sit a lot do not suffer more back pain or disability than more active people. See my chairs treatise for lots of detail on that.

There is conflicting evidence on all of these points, of course, but the controversy is the point: the signals are weird and erratic, not consistent and strong.

If not these stresses, then … what?

These failures of common sense are legion, especially in the life sciences, where the complexity is generally much greater than our paltry powers of inference.

There undoubtedly are some mechanical stress factors in back and neck pain, but our complex physiological vulnerabilities to those stresses is probably the real story, factors like sleep deprivation, a subtle pathology like hypermobility (which ironically tends to make people feel stiff), a vitamin deficiency, hormonal changes, or “inflammaging” (increased systemic inflammation from aging and metabolic syndrome), to name a few fairly straightforward examples.

Even just the perception of back fragility and pessimism make us more vulnerable to persistent pain, and maybe that is more of a problem than all kinds of trivial physical stresses put together. That fearful fire has been fanned by therapists selling “fixes” for mechanical problems with exaggerated clinical importance based on “common sense” instead of evidence.

Demonizing trivial physical stresses is clearly wrong: it sends the harmful message that our bodies are fragile, especially our spines. And yet it’s a message that both patients and pros embrace all too easily.

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This post was originally published in early 2019, and was re-published July 26, 2024, with numerous minor improvements and a new audio version. I don’t generally “maintain” blog posts (only articles in the main PainSci library), but occasionally I re-run an upgraded version — usually when I’m too exhausted to contemplate writing something new from scratch. 😜 It’s amazing how much work even “just an upgrade” can take (about 3 hours for this one), but that’s still easier than a new one!