Casey Viator went from 166 pounds to 212 pounds doing 14 full body HIT workouts in 28 days.
People are... let's use the word skeptical... and say the progress was due to Viator sneaking off to do extra training, steroids muscle memory, that he simply didn't gain as much as was reported, or a variety of other possible explanations.
This is a pretty in-depth article from a guy who knew Viator and Arthur Jones and complied the actual notes after the experiment.
The physical results reported, gaining that much actual muscle tissue in that little time, is something that science says basically shouldn't be possible. So there's that. But the general concept of the ultimate bulking routine being "train a lot, eat a lot, grow" is kinda basic and accepted. Put a genetic freak like Viator through a plan like that and I could kinda-almost see how something crazy could happen.