If you're not already familiar with the muscle confusion training concept it essentially suggests that one must rotate exercises often to keep your muscles guessing to achieve progress/results. If you don't, your muscles will adapt and results could become compromised.
I get why it's a popular theory. People like Tracy Anderson and programs like P90X have sold people on the idea that muscle confusion is absolutely necessary to incorporate into your training if you want results. And truthfully people do run situations where their progress comes to halt because their body has become accustomed to their workout routine.
But is it really necessary? How often should you "switch things up"? Daily? Weekly? Monthly? Every 3 months?
In my opinion, utilizing muscle confusion training to incorporate entirely new exercises and workouts on a daily or even weekly basis it not necessary. Will it keep your workout feeling fresh and avoid boardem? Possibly, but it's necessary to achieve results.
At the risk of oversimplifying, when you perform a new exercise your body does it's best to adapt in an effort to perform that exercise more efficiently the next time. That's a good thing! When your body adapts it means it's getting better, stronger, and faster at executing that movement. However, adaption occurs over the course of continuous work with enough volume and intensity for a given exercise, which typically does not occur over night.
Say for example, you'd like to increase the number of push-ups you can perform. Consider the results of these two examples:
Example #1: On day one of your training you do multiple sets of push-ups. On days two through 13 you perform various other upper body exercises. Day 14 you retest your push-up strength.
Example #2: On day one of your training you do multiple sets of push-ups. On days two through 13 you perform push-ups every other day varying the volume and intensity. Day 14 you retest your push-up strength.
Between the two examples, which do you think would produce better results? I'm putting my money on example #2. Would example #1 give you some results? Maybe but nonetheless I'm a firm believer that if you want to improve a skill you need to practice it.
Not quite convinced? Take a look at runners. Runners who are aiming for a faster pace or longer distance don't run once a week and take aerobics classes the rest of the time- they run. They most likely vary their volume (in this case miles). And they vary their intensity (pace) but they run.
In an article for T Nation, Strength and conditioning coach, Charles Staley, made a great comparison of muscle confusion to learning a foreign language.
"Think about learning a language in high school. If you take 4 years of French, you'll be quite proficient by the time you graduate, right? Now, along the way, there will be days (and perhaps weeks) where you're sick and tired of studying the subject, but that's the price you pay for personal development. If instead, you took French as a freshman, Spanish as a sophomore, Italian as a junior, and Japanese in your senior year, you'll be a lot less bored, but the price you'll have to pay is reduced competency. This is a universal principle of personal development, and it applies to the weight room as much as it does to the classroom."As a lifter, I squat, bench, and deadlift every single week. I may vary my sets, reps, intensity, and even perform slightly different variations (i.e. changing my grip or deadlifting off of blocks) of those lifts but I do them week after week and even after a year of doing so, I'm still getting stronger. If/when I stop seeing progress in my squat I will add weight and/or change my set/reps but I won't stop squatting. Is it fun and exciting? Not always but it works.
Even though I think the idea version of muscle confusion that's being sold to consumers of P90X is totally bogus, I do think the program has some benefits. (Tracy Anderson is a whole other story). I'm certain that if you can perform the moves with good form and avoid injury, you'll see improved cardiovascular endurance, and burn a crap ton of calories. There is no denying it's a hard workout. If the variety it offers is the trick to keeping you engaged or started in a workout routine then by all means, DO IT!
I'll be honest, when I first started training clients I gave them a completely new workout every week. I cringe at that practice now but I thought that's what they wanted. Even though I knew it wasn't necessary, I felt the need to keep them entertained. I finally realized that I might lose some cool points but a shiny, brand new workout every week (typically) wasn't in their best interest.
So how do you know how often to switch things up? That's a tough question to answer as there is really no one size fits all. If you're starting a strength training program for the first time or even just a new cycle I'd give yourself at least four-six weeks to evaluate how your body is responding. Keep in mind that even a slight change in sets, reps, intensity, grip, stance, etc can solicite changes. Results don't happen over night but with hard work, smart training, and consistency you can reach your goals.