I just can't make myself believe in any kind of "expert" advice on the "correct" way of sitting, standing, walking, running. The whole notion is based on this premise:

All vertebrates: <evolve for hundreds of millions of years, with nobody to tell them how to sit and stand>

Some random shithead, born some time in the 20th Century: "Okay, here's how you're doing it wrong."

And, of course, you can bet both your balls that guy has a book on the subject, for sale at all reputable booksellers. And probably some expensive-ass chairs and shoes, too.