This isn't a fad. I work with Dr. Blair at USC and he has been researching physical activity effects on health for the past 20 years. He is one of the leading exercise science researchers with over 2000 citations per year.
Since it hasn't been a topic in the press for those 20 years, I think that actually supports the idea that this is a fad. Fads are mostly disconnected from the slow progression of science. (I don't mean that makes it wrong, of course.)