People who move less may not just be lazy!
A new study shows a strong “link” — one of those notorious correlations — between physical inactivity and pain severity in older adults. This post isn’t so much about the results of the study as the fishy leap to the conclusion that inactivity is the problem and fitness is the solution. Because the result does not necessarily mean that sedentariness caused the pain (or that moving around more can prevent it). What it could mean is … wait for it…
Many people move less because they are in pain! The inactivity may well be a symptom.
Whenever you see science news about a “link” like this, remember that you can always interpet it more than one way, but often much more easily one way than the other — like “the dress” or a Rubin’s vase/face.
The Rubin vase is a famous example of a “bi-stable two-dimensional form,” which can be seen either as a vase in the center, or two faces on the sides. It’s a good symbol for the ambiguity of the correlations between things like exercise and pain that are often revealed by medical research. It’s not just that “correlation is not causation,” but that the causation could be one way, the other, or both, or neither! But once we’ve started “seeing” it one way, it is amazingly hard to stop.
This particular correlation is prone to being misinterpreted as evidence that inactivity is dangerous … even by the researchers themselves. There’s often a token disclaimer in research of this type — in this paper, it’s “given the cross-sectional design, the bidirectionality of these relationships should be considered.” Yes, someone should consider that! But the authors don’t: they just a nod in the direction of bidirectionality. The paper shows a clear bias in favour of one direction, and neglect of the other. The disclaimer isn’t emphasized enough, so I’m saying it louder: the possible “bidirectionality of these relationships” isn’t a minor thing! Knowing about the link alone, without understanding how it works, isn’t terribly useful.
While being more active is unquestionably a healthy thing, fitness is a rising tide that lifts some boats a lot more than others, and its more of a long-term preventative investment than a short term medicine for pain. So please be cautious about telling people (including yourself) that they need to get more active to solve their pain when they may well be inactive because of the pain.