There's no solid evidence for orthotics for most of the conditions they're prescribed for. They are good for rheumatoid arthritis and for high arches.
For other conditions, improved coordination can be a more effective solution.
Personally, I've only gotten plantar fasciitis from a chi gung exercise called swimming dragon, which I solved by not doing swimming dragon. However, I didn't have the problem with the exercise when I was younger, so maybe I should take a serious look at how I'm doing it.
Also, I cleared up flat feet for a while by doing an exercise about the relationship between hips and ankles from _Running with the Whole Body. I need to get back to that.
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