For you P90X-heads: There'a s big profile of Tony Horton, Beachbody, and the company's head honcho, Carl Daikeler, in the New York Times. Check it out here.
The guiding principle is to mix up routines and “confuse” the muscles so as to avoid hitting a plateau. So some days are devoted to dumbbells or resistance bands, in addition to old-fashioned push-ups and pull-ups. Other days are reserved for yoga or cardiovascular workouts that involve a lot of jumping and squats.
But Robert Marting, a personal trainer who sells his own exercise videos, says that “muscle confusion” is a time-tested principle of bodybuilding, and that the idea has been around since the early days of Joe Weider, a creator of the Mr. Olympia contest. Beachbody “kindly borrowed the principle and just retermed it as a training secret,” he says.
True enough, Mr. Daikeler says.
“Trainers love to give negative reviews of P90X, saying it’s not that special,” he said. “They are right. It’s not that special.”[Source]