Nobody today thinks there's any one exercise or any single technique that will induce a bigger rise in metabolism than anything else that requires the same effort and the same amount of recovery.

It's really pretty simple -- stimulus plus recovery equals a faster metabolism post-workout.

One often-cited study used a workout that lasted only 31 minutes, but included circuits of power cleans, bench presses, and squats. The guys in that study still had elevated metabolic rates 38 hours later.

Breathing squats probably boost metabolism because they're really hard to do, which means they're really hard to recover from.

As for Peary Rader gaining 100 pounds in one year, here's an explanation of his "squats and milk" program:

http://workout-routines.blogspot.com/2006/06/peary-rader-workout.html

I don't know if it's legend or myth, but I've read that guys of that era would drink a gallon of whole milk a day when they wanted to gain mass. (I assume none of them were lactose intolerant!)