We are working on this and did a related study which included a group of participants more sensitive than average to standing and sure enough- more frequent posture changes from standing eliminated discomfort in 100% of participants. If curious: https://www.sciencedirect.com/science/article/abs/pii/S00036...
Have not seen any scientific backing for this Cornell recommendation 20m sit duration.
Most relevant study I have found is that sitting harm (average sedentary bout lenght & all cause mortality) actually begins at ~10-11m, and increases from that point. https://pubmed.ncbi.nlm.nih.gov/28892811/
"A marked increase in mortality risk was observed at ~10 min/bout; suggestive of a threshold effect."
We have been working on a better solution to this the last few years and have a good answer if extended desk work focus is integral to your work.
The fundamental conflict is one of movement vs. focus (and health vs. career sadly), and we have found a way to introduce significant posture changes while doing work. https://www.movably.com/
We, also unlike basically every other chair company sadly, also put this to an independent research group. Our protocol was a simple sit-stand transition every 3 minutes, and the seems to be the first study to show a chair preventing pain without interrupting productivity. https://www.sciencedirect.com/science/article/abs/pii/S00036...
We are just launching something related. Basically the harm from static sitting actually begins at around 10-12 minutes and builds from there. The more often you can interrupt it before that the better, but of course that also starts impacting productivity. There are also many sitting health impacts from muskuloskeletal to metabolic and these kinds of studies might show benefit in some areas but aren't testing everything.
Our thought is if we can also build significant posture changes (sit-stand) more easily into the workday it can help a lot, and our first study showed this dramatically.
My guess is today's recommendations to move every 30m/45m or so were a compromise between ergonomists and employers given more frequent interruption was not practical in the workplace.
In our study 100% of participants reported no discomfort even compared to high end ergonomic chair. Aside from what our chair does it does show how impactful more frequent posture changes can be. https://www.sciencedirect.com/science/article/abs/pii/S00036...
Anecdotally, I can sit in a chair for hours, but sitting on a rock or reclining on the ground (things I do often) seem to cause my (45+ year old) body to "set in" and it becomes difficult to move afterwards.
