Why "Muscle Confusion" Might Actually Work for Hypertrophy | Ep 470
Is "muscle confusion" just bro science, or does recent strength training research actually back it up? You migh be surprised...
We get into how muscles grow, why exercise selection changes which regions of a muscle develop, and the role of muscle length in hypertrophy.
This episode covers the last decade of research on exercise variation and hypertrophy. These include studies on leg press vs. leg extension and on triceps and hamstrings at different muscle lengths.
We distinguish the original P90X version of "muscle confusion" from the systematic variation (aka periodization and mesocycles) that you can intentionally plan into your strength training programming.
This framing matters most for adults over 40 who've been told to pick a few compound lifts and add weight to the bar forever (sound familiar?).
Join Eat More Lift Heavy, the 26-week coached program where adults over 40 build the nutrition and training skills to preserve muscle, lose fat, and manage their physique for life.
Timestamps:
0:00 - Muscle confusion and exercise variation
2:25 - Where "muscle confusion" came from
4:00 - Mechanical tension and progressive overload
5:52 - Muscles as regional structures
7:30 - Regional hypertrophy in the quads
10:24 - Muscle length and hypertrophy
14:30 - Strategic exercise selection
15:45 - Training programming for adults over 40
17:01 - 3 rules for planned variation
20:42 - Caveats on variation
23:35 - Bonus: lengthened-position swap per muscle group
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Philip Pape: 00:00
If your training program looks basically the same as it did a year ago, because every coach tells you, just pick your lifts and add weight to the bar, but your muscle growth has stalled in spite of doing everything right. This episode is for you. We're gonna look at research from the last three years in the area of quote unquote muscle confusion, and some of it's gonna surprise you. I'm gonna show you what kind of exercise variation actually does grow more muscle, which ones waste your time, and a simple way to balance all of this along with your progressive overload. Welcome to Wits and Weights, the show that puts a popular piece of fitness advice under the microscope, finds the hidden reason it doesn't work, and gives you the deceptively simple fix that does. I'm your host, Philip Pape, and we're gonna talk about the concept of muscle confusion. It probably sounds like something from the 90s, from P90X, from classic bodybuilding days, you know, random workout, shock the muscle, uh, progressive overload, what's that? Maybe not tracking, you know, none of the good stuff we often talk about these days. And a lot of coaches, you know, even evidence-based for the last decade or two have said, hey, that that that concept is nonsense. Let's focus on just muscular tension and growth and progressing our lifts. And I generally agree. I still generally agree. But honestly, there is there are aspects of bro science that do hold up in a way. And I like to address these because I think it's fun to tease apart reality from myth. And the phrase muscle confusion, I think, covers different things, two specific ideas, and we're gonna separate those. One of those ideas doesn't make any sense at all, complete nonsense. The other, the one that is a real driver of muscle growth, uh, especially the older you get and the more that you train, might give you this extra advantage once you understand it. And then stick around to the end of this episode because I'm gonna give you the single highest payoff exercise swap for each major muscle group. If you only change one thing in your training this week, this bonus at the end is the one that you can incorporate. All right, in this episode, I'm gonna cover why the original P90X version of muscle confusion was indeed broscience and what Tony Horton himself has admitted about it. The actual research from the last two to three years on regional muscle growth and muscle length training, and then a simple rule of thumb to set up your accessory work so you're getting the most out of every
Philip Pape: 02:25
session. All right, let's start with what muscle confusion originally meant, because I think a lot of people argue against it without realizing what they're arguing against. Okay, so the phrase actually predates P90X. We can go back to Joe Weeder. Joe Weeder was writing about something called the muscle confusion principle decades ago in the old bodybuilding magazines, and then it finally hit, I guess, what you'll call the mainstream, is in the infomercials about 20 years ago, the mid-2000s, let's say, Tony Horton. And the pitch was that your muscles get used to exercises and then they stop growing. So you need to constantly shock them with new movements to force adaptation. Monday is Plyo, Wednesday is Kenpo karate, Friday is yoga X with weighted curls. You know, you get the idea you've probably done something like this. Maybe you're laughing out loud right now. And if it kind of sounds like nonsense to you now, especially if you listen to Wits and Weights, you're definitely not alone because Tony Horton has admitted on multiple podcasts that it was a marketing term. Muscle confusion was a marketing term. The team made up the phrase as a label for what was just variety. That's it. And we call this something else generally. It's called periodization. So generally that, you know, labels are mean a lot, especially when we think about the fitness industry and marketing. There was another interview where he said muscle confusion and periodization are the same thing. So again, variety. That's really what we're talking about. And so that's the piece we're gonna say could work for certain reasons. We're gonna get into it. Now,
Philip Pape: 04:00
the bro science piece of this is the idea that muscles, you know, memorize your exercises or they get bored or whatever. Nonsense. Skeletal muscle responds to mechanical tension. That is the primary driver of hypertrophy. And you need sufficient volume with that mechanical tension to induce progressive overload, right? You have to have enough of the stimulus over time and the tension to grow. I mean, you don't want, you can't use mechanical tension today and then skip training for three weeks and hope for it to work because you're going to get detrained. So if you do the same lift week after week and you keep adding load or reps because you are pushing close to failure and inducing muscular tension, your body will adapt and you'll get stronger for next time. And that is the process. Very simple, full stop. You don't need muscle shock or any of this crazy nonsense. Randomly changing exercises, especially if you're doing it every session, that actually destroys the thing that drives long-term growth, which is your ability to track progressive overload and get enough frequency and stimulus on a specific movement pattern. Can you still grow in some ways? Yes, there are definitely programs where they rotate a lot and you still grow, but it's very hard to tell that you're getting stronger on your bench if every Wednesday is a completely different pressing variation drawn out of a hat. And again, it doesn't preclude growth if you're stimulating the same muscles. It just may not be very efficient. So when we push back on muscle confusion, there's a lot of validity to that. And the idea of picking a small set of exercises and just sticking with them is a great way to drive progress. And I would recommend that to all beginners and most intermediate lifters. And I've said that on this show many, many times. It's why I do like programs like starting strength. They're very basic compound lift style programs, especially when you're a beginner.
Philip Pape: 05:52
So we want to talk about some new evidence though in the last few years that addresses a narrower question. Does it matter which exercises you pick? And does loading those same muscle groups from multiple angles because of that variation produce different growth than loading it from just the one angle you get in a single movement pattern? And the answer, surprisingly, maybe, is yes. Yes, it does. And it does so in a way that has some practical implications for your accessory work. And that's where things get useful on this show. We want to tell you how to actually implement this in your real life. Okay, so to understand why exercise selection matters more than we used to think, I want to drop an assumption on you that a muscle is a single object. This is an assumption many of us have, right? That like there is a muscle. That is not true. A muscle is a structure and it has regions. For example, the biceps has a proximal portion near the shoulder and a distal portion near the elbow. So proximal is near, distal is far. The quadriceps, right? The quads of your leg have four separate heads, hence the word quad. Each head has a top, middle, and bottom. The triceps has a long head, a lateral head, and a medial head, right? Tri-three. And they all have different geometric relationships to the shoulder and to the elbow. So when you do an exercise, the load gets distributed unevenly across that muscle, that muscle belly. And it gets concentrated in regions where the geometry of the exercise puts the most tension. The more you understand that, the more you understand why different exercises produce different growth patterns, even when they technically target the same muscle group. So even when you're when you swear in the gym that I'm training my chest, you might be growing different parts of your chest. Case in point, flat bench versus incline. For anybody who knows anything about that at all, you know that they hit different parts of the chest. So I want to share some data because numbers are really helpful. I'm an engineer, I like data, and I always like to tie it back to metrics and numbers. Um, and this some of this stuff might surprise you. So it's interesting. There's a foundational study by Fonseca and colleagues in 2014. They took young men and split them into two groups. One group did only back squat for 12 weeks, another group rotated among squat, leg press, deadlift, and lunge across the same training week. So all back squats versus four different leg exercises each week. But the total weekly volume was matched. The total quad growth was the same between the groups or similar between the groups, but when the researchers looked head by head, so muscle, muscle head, the squat-only group had gaps in certain heads of the muscle, the rectus femoris and the vastus medialis. You don't have to know what these are, those are, you can look them up. The varied group, the group that had multiple exercises, grew all four heads of the quad more uniformly. And so that was kind of the first sign in the literature that exercise selection affects which regions of a muscle grow beyond just how much total growth happens. Now, again, we're talking hypertrophy, we're talking muscle growth. A lot of this growth, a lot of this isn't gonna translate one-on-one with strength if that's your goal, right? There's significant overlap for sure. But if you, for example, have already well-developed heads of the muscle, you may benefit more from the big movement patterns in a systemic way. So that's just a caveat. Anyway, fast forward to very recent research back in 2024, Burke and colleagues, they did an in-person or a within-person study. Uh, and this one's pretty compelling. They had each participant train one leg with leg press and the other leg with leg extension for eight weeks. So within your own body, you're training each leg different ways. Kind of interesting, right? So one leg gets a leg press, the other the leg extension, and then they measured the rectus femoris and the vasus lateralis using ultrasound. So again, two heads of the quad. And what they saw is the leg extension leg grew the rectus femoris more, and the leg press grew the vasus lateralis more. So same person, same effort, different exercise, different regions, different regions growing. And the statistical probability of this correlation was as high as 0.99, which is almost a perfect correlation. So that's kind of the regional heads finding. The second
Philip Pape: 10:24
piece of this mechanism is muscle length. And this one might be even more important because you've heard a lot of talk about the short and long positions of the muscle and lengthened partials, things like that. So now there's a series of studies showing that loading a muscle in a lengthened position produces more growth than loading it in a shortened position for the same number of sets and reps. And just quick caveat before you jump to ah, I see, see, I need to be training lengthened. We're gonna find that it's still beneficial to train the full range of motion for a variety of reasons. But let's just look at this. So Mayo and colleagues 2023, they had their subjects do triceps extensions overhead with one arm and triceps pushdowns at the side with the other arm. So again, this is a within person type of deal. And both arms got the same training volume. So after 12 weeks, the long head of the triceps had grown 29% on the overhead side and only 20% on the pushdown side, the whole triceps grew 20% versus 14%. Now, isn't that interesting? Isn't that interesting? So in the overhead, now I've always thought or I learned a long time ago that overhead triceps work tends to be, tends to blow up your triceps more, and that it's because of the length and position, because of that extra range of motion. By the way, the overhead group used less weight than the pushdown group. Now, not that it translates directly, but that's just interesting, right? So the length and position was the the real key variable here, not the load. The overarm, the overhead arm grew more despite working with lower absolute weight on the bar. I think I said that right, right? Yeah, the overhead group used less weight but had more growth. So that's interesting. The same lab, they tested hamstrings the same way. So they did a seated leg curl where your hip is flexed, your hamstring is stretched over the hip joint, right? A seated leg curl versus a prone or lying leg curl where the hip is extended and the hamstring is shorter. After 12 weeks, the total hamstring volume grew 14% on the seated side and only 9.3% on the prone side. So it's 50% more growth from the same movement, but done in a different muscle length. So the seated seems better than the prone. And then in 2023, another group looked at the big calf muscle called the gastrosinemius. The group that trained mostly through the bottom stretched portion of the range, remember, this is calf raises. We talk about it all the time, how important it is to stretch at the bottom, have that height, and really have that ankle come down. So you stretch at the bottom, produced more than twice the muscle growth of the group that trained mostly through the top shortened position. Same load on the bar. The difference just where in the range of motion the muscle was working the hardest. So I think you get the picture from all of these studies. The same muscle can respond differently to different exercises and to different parts of the range of motion. And the mechanism here is straightforward. Mechanical tension drives growth, and different exercises apply that tension to different regions of the muscle at different points along the strength curve. So it's not muscle shock, muscle surprise, novelty effect. It's just physics and geometry. That is fascinating. As an engineer who loves to explain things with science, that is so cool. It still comes down to mechanical tension, right? But now you're talking about how you get to apply that tension in the proper way for what your goal is. And this is where the idea of imbalances actually carries some validity, right? Because if you're overdoing it in one region of the muscle, um, you could get an imbalance. Now, I'm gonna go way back to my starting strength days and say, you know, if you're if you're training the full movement patterns, by definition, you shouldn't be as imbalanced because everything's working together as it should. However, because of life, because of injury, because of improper movement, because of, because, because we do still see some level of imbalance. Plus, a lot of you want to do hypertrophy and grow your muscles and look better and all that. And so you might even create imbalances by training too much of the same thing, for example. And that's kind of what we're getting at when we talk about this concept. So that brings us to strategic exercise selection, where you cover different regions and different muscle lengths to drive more uniform growth across the whole muscle. And that is in concert with the major movement patterns, which also, in a sense, do a similar thing, but may hold you back if your bottleneck is a weak area of your muscle and the movement pattern doesn't stress that muscle group. Does that make sense? That's where I think variations can blow you up if you are in that situation. Whereas for others, they may not add anything and they may just add fatigue and volume that are unnecessary. So it's very interesting. All right, now if you're hearing this and thinking, all right, it all makes sense, but I don't want to spend a ton of time researching which exercises go with which heads of my quads. All right. And I get it. And you know, most lifters don't want to be their own programmer. They want to lift, they want to see the numbers go up, they want to know that someone else has thought about the program or the training. And that's why we built Eat More Lift Heavy. This is our program, Eat More Lift Heavy, where the programs are available already to cover a variety of goals, days per week, equipment, and skill level. And we assign it to you on day one based on what's going on with your intake, your life, your equipment, your experience, your goals. Right? We don't just give you a content library of a million templates or an app that has unlimited selection. We actually tell you here's what you can do to make the most out of where you are right now. And typically they're based on compound lifts with accessories rotating on a certain type of schedule. And the more advanced you are, the more of this kind of rotation and variation you might have. So this muscle length and regional growth stuff I'm talking about today is baked into how I like to structure our programs. And Coach Carol, who is also in Eat More Lift Heavy, she has written up some excellent training programs as well. Because many of you, you can't afford to spend hours and hours trying to research this stuff. So Eat More Lift Heavy, it's a 26-week coached program built around these ideas. Eat enough, lift heavy, progressive overload, know exactly what to do, focus on one thing a week. Don't get overwhelmed. You know what to do next. You focus on your biggest constraint, you make progress, you get accountability. It's as simple as that. There's a lot of extra bells and whistles, there's live coaching calls, there's a private community, there's lots of resources. That's all fine and good. But the main thing is that you actually implement the information to make progress. If you want to learn more, go to eatmore liftheavy.com, check it out, go to eatmore liftheavy.com. All right, I want to get practical
Philip Pape: 17:01
now. How do you use this stuff? Okay, assuming you're not, assuming you don't join our program and we just make it easy for you and you want to program your own stuff. How do you do it? I'm gonna give you three rules. If you apply these three rules, you'll get the most benefit from what the research tells us works. And again, it all comes down to mechanical tension, but it's more complicated as always. And you're gonna get the progressive overload that does build your muscle. All right, rule number one anchor your compound lifts. What I mean by that is the main lifts in your program shouldn't change much. Okay, until you get into advanced, like something like conjugate or powerlifting style thing, anchor your lifts, your squat or your hinge variant, your horizontal press, which is usually a bench press of some kind, vertical press, rowing, andor pull downs. Okay. I think I covered them all, or deadlift as well. I said hinge variant, but squat and deadlift. So even if it's a Romanian deadlift, even if it's a JM or an AD press, whatever, the variation is keep them stable for like eight weeks, maybe 12 weeks. Don't rotate them. All right, that way you build the neuromuscular adaptation. Your body learns the movement patterns. It's essentially a skill, and you'll be able to load it heavier from session to session. You're gonna be using your natural movement patterns. I think that's really, really important. All right, don't switch around from leg press to split squat to step-ups and just all over the place. Do not do that for your main lifts. Okay, so that's the first one. That's like your stable platform for the program. Rule number two is to choose complementary exercises, but rotate them on what's called a mesocycle. This is it's not too complicated. A mesocycle is just a long enough period of time, like four or six weeks, maybe eight weeks, where you swap out your accessories to start hitting different regions of the muscle groups. Okay. And you might already be using hitting different regions within your week, like if you do triceps on two days a week and you hit the long and short heads, you may, or the two, two, two of the two or the three of the heads, you might already have that built in, but then you're going to swap things out for slight variations after, say, six weeks, even if the compound lifts stay the same. And that gives you some variety as well, makes it fun. It's something to look forward to, but you need a long enough runway for your biceps, your triceps, your calves, your hamstrings, your delts, you know, direct chest, like pec work, that you actually make progress and then you rotate over these mesocycles, these blocks within the big block. And then rule number three is at least one exercise per muscle group should definitely load that muscle in a lengthened position. Now, if you're doing full range of motion, you are hitting the lengthened position generally, but certain exercises will hit it harder. Right? So if you're gonna pick two to three exercises per muscle group across the week or across your block, make sure one of them stretches the muscle really nicely under load. So for triceps, that means overhead. Like have an overhead thing in there. Oh, I'm always thinking triceps have something overhead. Don't just do press downs. For hamstrings, a movement where your hip is flexed. Okay, where your hip is flexed. For chest, a fly with a deep bottom stretch or press where the dumbbells go below the line of your chest. For biceps, an angle where the arm is behind the torso. So in this case, I love incline bicep curls. So I think you get the pattern, right? I think you get it. And I'm gonna give you a specific swap for each muscle group in the bonus at the end of today's episode. So hang tight for that. That's it. That is how you upgrade your programming to take advantage of this and get a really effective workout. You anchor the compound lifts, you rotate your accessories using a mesocycle, and you hit one lengthened position movement per muscle group. All right. Now I
Philip Pape: 20:42
want to address something that I know you're probably thinking, because I love nuance. We always lose nuance. That's why I like podcasts, long form. Okay. I am not saying that variation is more important than volume or progressive overload. Not even close. Okay, you have to go near failure on enough sets with enough frequency and progressively overload those lifts. You have to eat enough, you have to need enough protein, probably enough carbs. Are you sleeping? These matter way more than exercise selection. I'll tell you that right now. Okay. I'm also not saying that every study tells us this is exactly how it is. There are some studies that suggest maybe the benefit is really in the combination of all these things. And you're gonna get that just from a normal, well-structured program that we've talked about today. And I'm not also not saying you you make this a random variation where you're constantly switching around because that is not gonna help you out either. All right. I would call variation a refinement on top of the fundamentals. That's it. It's a refinement on top of the fundamentals. It's something to think about. One little thing I didn't mention, I'm just throwing it in there right now, is a finisher. This is just a bonus. You can add a finisher at just the lengthened position. Look it up, go to Google or YouTube, check it out, what I'm talking about. Just look up lengthened partials, and you can use that as a finisher, might. Be an extra fun thing to try. So that is where we land on this with the principles. Before we wrap up, I want to remind you that I promised I'm going to give you a single highest payoff swap for each major muscle group in just a second. But if any part of this episode connected with you, if you realize I haven't been running things quite the right way for my program and I'm not quite sure what to do, that is why we built Eat More Lift Heavy. It is going to level you up so much in your skills, which is my mission in life is to help you build these skills so you don't need to depend on another coach again. I'm sorry to all the other coaches listening where I'm ruining your long-term revenue per client or whatever. But I want people to fire me. I want people to learn and be excited. And you know what usually happens is you learn, you get excited, you grow, you build muscle, you lose fat, you look better. You're like, okay, what's next? I want to level up to the next skill. And that's how this thing should work. So eat more lift heavy, eatmore liftheavy.com, a 26-week coach program, primarily for adults over 40, to build the nutrition and strength training skills to build and preserve muscle, lose fat, manage your physique and sustain it and eat well and sustainably eat for the rest of your life. No diets, okay, no cutting carbs, none of that nonsense. You're gonna get a coach-assigned training program, monthly live coaching calls, a community where you can get accountability in addition to just the program itself, which is one skill per week that you focus on. It's very achievable. And it's an incredible program. Go to eatmoreliftheavy.com. I would love to see you there. You can learn everything about it on the page, eatmoreliftheavy.com. All right. If
Philip Pape: 23:35
you only change one thing in your training this week, swap one accessory per muscle group for its lengthened position version. So here we go. Triceps. Trade cable pushdowns for overhead rope or dumbbell extensions. Hamstrings, trade one set of prone leg curls, that's lion leg curls, for seated leg curls. Biceps, swap a preacher curl for an incline dumbbell curl. Okay, where your arms hang behind your torso. Your arms should be basically straight down when you're sitting. Chest, swap a flat dumbbell fly for an incline dumbbell fly with a deep stretch at the bottom. Alternatively, you can use a pec deck if you have one available. Calves, trade one set of standing calf raises for one where you let your heel drop as deep below the platform as you can. Now, this may be the same exercise, just positioning it differently, getting a higher box or platform or whatever. That's it. I think you can experience some more growth by just making these tweaks and have fun in the gym next time you go train. All right, until next time, keep using your wits, lifting those weights. And remember, growing more muscle comes down to loading the same muscle well with mechanical tension from more than one angle. Nothing fancier than that. I'm Philip Pape, and I'll talk to you next time here on the Wits and Weights podcast.
