This is a repost from the P90x #053 newsletter and has some great information on how P90x works and why it works.
By Steve Edwards
With the popularity of P90X, the term Muscle Confusion™ is getting a lot of play in the media. And while many people credit it as the reason P90X is effective, not many people understand what it means, much less how it works. Today, we'll briefly examine what Muscle Confusion is and why it's so effective.
Peaking
I think it will be easier to comprehend if we work backward. The whole idea is based around creating a fitness peak. P90X starts and ends with a fit test. We don't have you take the fit test mid-program because your progress curve is not supposed to be steady. Instead, the program is designed with phases that take a while to master. As you are attempting this mastery, confusion reigns, and your performance may not be all that great. But when you put it all together, and the various bits that have been confusing your body all come together, the result is a period of peak fitness.
One of the concepts that seems the hardest to impart to our P90X athletes is how (or why) to peak. Most Xers don't consider themselves athletes because they lack performance-oriented goals—they just want to look good or feel better. But it's important to understand that all training at the level of P90X adheres to athletic principles. And athletic training always builds around a peak period when you need your body to perform at its best. Following this template doesn't just work for athletes. It works for anyone training at a high level.
Periodization
The entire theory of Muscle Confusion is based on something called periodization, which is basically training in targeted cycles that keep your body from getting too used to your schedule. The goal of periodizational training is to minimize performance plateaus and keep your improvements happening for a specific amount of time. All periodized programs are structured with a progression of training blocks designed around a peak. This is why most of our customers get their best results during the latter phases of our programs, especially with P90X.
Adapt, master, transition
The training blocks are laid out with a plan. Your body begins each block faced with something new. This forces you to adapt to it. The stress of this process leads to accelerated improvements. When your body is used to the new regimen, it has a short period where it makes even greater improvements, which is called a growth or mastery phase. Finally, you get so used to the training that your results begin to plateau, at which time it's best to transition into something else.
Timing is everything
You don't always want to be in a state of confusion, so it's important to be aware of when your body should transition. This can be difficult, but with experience, you get better at it. Moderately intense programs like Power 90®, customized for clients who are out of shape, have a structure that is less rigid because the adaptation period takes longer. Conversely, the fitter you are, the quicker your body reacts to training and the quicker it adapts.
Most science shows that a 3-week-on, 1-week-off cycle of training is about as short as you can go to maximize the adaptive and growth phases. That's why we've used this in P90X. This isn't set in stone. If you read the fine print of your guide, you'll see that we do recommend that you set each block to your own schedule. Ultimately, what's important is that you halt the growth phase before a plateau occurs and that you see the full cycle through to its end.
Don't get happy! Attack!
A friend of mine was in a wrestling tournament and his opponent's coach kept yelling to his wrestler, "Don't get happy! Attack!" His vitriolic approach was so over the top that my friend started laughing and almost lost, but his message was a verbal equivalent of Muscle Confusion. You teach your muscles something new until they master it. Then, before they get happy, you launch into something else and force them to respond.
Although he wasn't speaking of Muscle Confusion, I think Arnold Schwarzenegger summed the process up quite succinctly in the film Stay Hungry. When asked why he didn't take it easy more often, he said, "I don't want to get too comfortable. I'd rather stay hungry."