What’s MOST important for muscle growth & strength?

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What are the most important things you have to do in your training to build muscle and strength?


00:00 Introduction

00:17 2023 meta of 178 studies

00:47 2023 umbrella review

01:50 General trend – volume and intensity

02:13 Why is training volume so important?

07:19 Why is training intensity important for strength?

11:11 What about Mike Mentzer, Dorian Yates?

15:34 Conclusion


What are the most important things you have to do in your training to build muscle and strength? In this video, I’m going to answer that question based on an analysis of over 200 studies. Specifically, I’m going to discuss two new meta analyses that were very, very large. The first math analysis we have here from 2023. So very new. They analyzed 178 studies and they concluded the highest ranked prescriptions for strength involved higher loads, whereas the highest ranked prescriptions for hypertrophy included multiple sets. So basically they concluded that intensity is most important for strength and volume. Measured as sets is most important for muscle growth. These results coincide quite well with another super huge review. Again, a new one, an ultra big-picture umbrella review of 44 systematic reviews. So that’s 44 other reviews, each of which contains many other studies.

And the only super consistent predictor they found for muscle growth and strength development was volume, and the effect was much stronger for muscle hypertrophy, so muscle size development than for strength development For strength development than for strength development For strength development the most important variable again was training intensity. So these are super, super big picture reviews and I don’t recommend reading too much into the details of the reviews. I think these are mostly suited when you just throw all the data together and we see, okay, what really works super consistently and has a large effect it’s not something that works for certain individuals or it’s not some variable that you can make it work with the optimal program, no. These things work in everyone basically all the time. We’ll get to more later on exactly what the optimal volume and the like is, because that will vary per individual. But as a general trend volume for muscle growth and intensity, so heavy training loads using heavyweights, especially 1-5 RM weights, with weights that you cannot lift six or more times is most important for strength development. In the researchers own words, they concluded that resistance training volume number of sets influenced muscular strength and hypertrophy.

So why is training volume so important? Well, the number one variable that influences muscular development, and muscle growth in particular is mechanical tension on the muscle fibers and volume, especially the number of sets is essentially a measure that measures how often we impose this stimulus on the muscle. So every time you do a set, this is a stimulus, it puts tension on the muscle and it basically sends a signal to the muscle, okay, hey, we need to get bigger to resist, to adapt to this tension. When you do multiple sets, you’re basically giving it repeated signals. So this makes perfect sense. However, why is there such a big difference between strength development and muscle growth? And why is training intensity important for strength development?

In fact, even more important than training volume in most of these analyses, whereas the researchers found actually that training intensity was not important in either analysis for muscle growth. this finding has become known as the hypertrophy zone myth. You’ve probably seen images where there is a label of strength on the 1 to 5 rep range and a label of hypertrophy on a 6 to 12 rep range and then a label of endurance on the 13 plus rep range. In reality, the hypertrophy zone, it’s not 6 to 12 reps, it’s actually possibly 1 to 30 reps. When you go over 30 reps or 30% of 1RM. it seems that the resistance is too light to simulate maximum tension on the muscle fibers and thereby muscle growth and strength development. You will still be able to stimulate some gains, but not maximal gains When you get super heavy, when you get to the 1 to 5 rep range. It is true that on a set by set basis you may have less muscle hypertrophy with say sets of two than sets of six. And that’s not because it’s inherently worse. Because if you logically think about it, heavy weights impose higher tension on the muscle fibers. So per rep, this should be better. Indeed, they probably are.

But you’re doing so few reps that the time under tension is not sufficient to stimulate maximum muscle growth. So there seems to be a threshold around 85% of 1RM, say five reps if you want to be conservative, if you’re staying over 85% of 1RM and over five reps per set or at least five reps per set and no more than 30 reps per set on the lighter than 30% of 1RM, then muscle hypertrophy on a set by set basis in these studies is the same. So you can do sets of 18, you can do sets of 28, you can do sets of eight. All of these sets on a set by set basis, so three sets of each in many, many studies now result in the same amount of muscle growth. That’s called the hypertrophy zone myth. and the reason that light weights can be as effective as heavyweights for muscle hypertrophy is because when you train with light weights, then as you accumulate neuromuscular fatigue, this lowers the recruitment threshold of higher threshold motor units.

So basically that the big guys with more type II fibers, more muscle fibers in general, they can produce more force. The big guys only come in to help when the little guys get tired. That’s basically the principle that regulates motor unit recruitment, also called the size principle, the bigger motor units, the higher threshold motor units. They kick in, as you get fatigued, to help. So in the end you’re still recruiting all the motor units. If you do a very heavy sets, say six reps, five reps. Most research finds that around 80% of 1RM you get full multi-unit recruitment. So if you start a set at say seven reps, six reps. Now from the start you’re recruiting all the motor units, you get tension and all of those muscle fibers. Because the motor unit is basically a motor neuron that regulates the activity of a lot of muscle fibers. All of these muscle fibers, you impose on them because they contract.

The contraction, the force production of the muscle fiber – that is the tension. Force production and tension inside the muscle are basically the same. That’s called active tension. There’s also passive tension. Now, if you do heavy sets, with say six reps, then you get tension on all of these motor units, everything in the muscle basically at the same time from the beginning to the end, right? If you do a very light set, then you don’t get tension on all of the motor units from the start of the set. But as the set progresses, as you can see in this image here, you get something like this where on the horizontal axis over time we have the increasing duration of the set and also the accumulation of neuromuscular fatigue. And on the Y axis, the vertical axis, we see the total number of active muscle fibers and they’re also organized by muscle type. You see that the type I fibers, they are active from the start, no matter how light the activity is, some type I fibers are going to be active and then as you get more fatigued, you come closer to failure then the type IIA fibers, then the type IIAX fibers and the type IIX fibers, they all kick in later to help.

And in the end, you’re still recruiting all of them. So you’re still putting tension on all of them and you are getting a similar amount of muscle growth from the set as long as you train close to failure or given the same proximity to failure in general, whether you do a set of 17 reps, 27 reps, 7 reps, it’s going to result in the same amount of muscle growth because in the end you’re recruiting all the muscle fibers anyway. So that’s why intensity as in your relative load, how many reps you do, does not influence muscle growth within the hypertrophy zone, the hypertrophy zone 2.0 if you will, of say 5 to 30 repetitions.

Now, why then is training intensity important nevertheless for strength development? Well, the reason for that is that while all motor units are recruited at some points with a light set, you’re not recruiting them at the same time. So muscle activity at any point in the set, as you can see in this image here, for example, is relatively low with a low intensity set compared to a high intensity set. And you want muscle activity levels to be synchronized, you want all of them at the same time so that you can synchronize the activity of all of the motor units of all the muscle fibers together.

Because strength development is not just a function of muscle size – morphological elements, which is simply how big the muscle is, but it’s also in very large part driven by neural factors. So strength is like a racecar where The engine that’s the size of your muscles is a big factor. But there’s also a huge factor in the skill of the driver, which is the skill of your motor cortex, the part of your brain that governs movement.

So if you have a very skilled driver, very skilled motor cortex – it can coordinate all of your muscle fibers very well. In order to do that, you need very high muscle activity levels. So that all of the muscles are active at the same time at maximum capacity. This maximizes force production and that’s why you need very high levels of muscle activity to maximize strength development. More intuitively, you simply need very high force production and maximal strength performance to train maximal strength. The body gets better at what you do, and this much greater reliance on neural factors of strength development versus muscle growth also explains why muscle growth is much more strongly influenced by volume than strength is.

Strength is influenced by volume, but not nearly as much as muscle growth. For muscle growth, volume is king, Volume is the most important variable in your training for strength development training intensity is king, at least in the short run, because in the short run, the neural factors are much more important than the morphological factors. It takes a long time to build size, and if we look at records from powerlifting, for example, we see that strength and size correlate pretty much linearly because you’ve maxed out the neural factors.

At that point, we can see that the correlation between strength and muscle growth is basically linear. And what that means is that, yes, size builds strength, but you need a lot of size to improve your strength, specifically to get your levels up by 20%, say 100 to 120 kilogram bench press. That’s going to take 20% size increase in the pectorals, the delts, the triceps. So that’s a lot of muscle growth. It takes a long time to build that. So in that sense, I think these studies are a little bit short sighted because the contribution of volume to strength becomes much more significant over the long run as you need to build a continued size to increase your strength.

You know, at some point you’re going to max out your strength. That takes a long, long time because the nervous system is very plastic, it means it’s very adaptable. But eventually you’re going to have perfected a movement, say, the bench press technique, muscular coordination, antagonist coactivation is low. All these factors that make you a good bench presser from a neural point of view, how your muscles are coordinated by brain At some point that’s basically capped out. And the only way that you can get bigger after that point is to gain more size. That’s why over the long run size and strength are very tightly correlated to lifters. In fact, in powerlifting research, we see that the correlation is so tight that you can basically forgo the powerlifting competition altogether because you can just put them in a DEXA scanner. You get pretty much the same ranking. And I think a very ironic finding that powerlifting competitions, which are known for being all about strength and not about size in reality, the rankings are pretty much simply their fat free mass indexes.

So that explains why, over the long run, strength and size correlate very neatly. Whereas in the short run, strength is much more influenced by neural factors and thereby by training intensity than by set volume. Over a long run, set volume is still very important for strength by virtue of increasing muscle mass, which will improve your long term capacity for strength development. Now, I know that at this point some of you are going to be wondering, okay, yeah, but what about Mike Mentzer, Dorian Yates, what about high intensity training? Because that seems to violate the central principle here that volume is king and indeed volume is king. And training to failure, which is what they advocate as being more important – is not in fact, in both of these analyses “set end point” as they define it and one of them and “volitional fatigue” as they define it in the other one were not consistently predictive of muscle growth or strength development. And I recently did an extensive video on training to failure.

So you can find all the details there. Training to failure does help – on average, if we look at more granular data, does improve muscle growth and strength development, especially muscle growth. But it’s a very small effect that’s explained by the increased volume that you do – if you do more repetitions. it’s not nearly as important as doing more sets in most circumstances. So for more details, you can check out that video. regarding Mentzer and Yates and looking at these single individuals, for one, it makes no sense to look at single individuals. If you look at my recent short I did on what makes the most difference, you can see it’s mostly genetics and training hard, and they had both of that in check.

And then drugs are also, of course, a huge factor. Moreover, if we look at bodybuilders in general, high volume is actually a super widely practiced element of pretty much all successful bodybuilders, barring a few exceptions, that of course garner all the interest of people that would like to do low volume, myself included. I would like to do low volume. I push to failure because that suits my personality a lot better. But it’s simply not what the data support volume is king when it comes to muscle growth and training to failure is not nearly as important.

Now, when we are talking about volume, what exactly do we mean? In the analysis they define it as a number of sets. Indeed, most research finds that the total number of sets per muscle group per week is the best predictor by far of muscle growth. And that’s because it’s a measure of the total amount of mechanical tension imposed on that muscle. So this confuses a lot of people. When I talk about training to failure, for example, saying it does matter to some extent because it increases volume.

And in that context, the volume means repetitions or total amount of work, which is weights multiplied by repetitions multiplied by number of sets, total amount of work volume, which is also a definition that researchers often use. And we see that in some contexts total work, as in total repetitions, is important. For example, with rest intervals, exercise order and training to failure. However, in other settings, set total set number is most important and as I just discussed, when it comes to sets of different number of repetitions, we see that they stimulate similar amounts of muscle hypertrophy. Now, there’s actually a very simple solution that explains why in some context set volume and in other contexts, repetition volume is more important If the weight is kept constant, the total amount of tension imposed on the muscle is constant – in that setting, the total amount of repetitions becomes important.

That’s why we see with training to failure There is in a bit more granular research, not these super big-picture umbrella reviews, we do see effects that training closer to failure helps to some extent with gaining more muscle because you’re doing more repetitions, therefore extending the total amount of time under tension. However, when we change the weights, so when we’re looking at training intensity research by changing the weights you’re changing the muscle tension, right? The weight and the muscle tension, they correlate linearly. So if we are looking at high versus low repetitions, then we see a tradeoff between the intensity per repetition and the time under tension essentially.

So that tradeoff is largely neutral when it comes to higher vs lower repetitions, you get in the range of 5 to 30 repetitions roughly. However, what the weight is kept constant, like with training to failure, We do see these effects. They are smaller because of course we’re talking about a few repetitions as opposed to a whole set of repetitions. And that explains why in some context. So total amount of sets is most important and indeed big picture like these reviews show, total number of sets per muscle group per week is the single most important factor that governs how much muscle you are going to built in that specific muscle. And for strength development, it’s training intensity – at least in the short term. In the long run, you also need muscle growth to build extra strength.

So to conclude, if training intensity is the most important thing for strength development and training volume is the most important thing for muscle growth, what training volume and what training intensity should you be using? Well, for strength development, it basically seems be the case that the heavier you go, the bigger your strength gains – in trained individuals. Most studies in untrained individuals do not find very appreciable differences in strength development. So typically in untrained individuals or novices in general, I would say don’t bother going with 1RM attempts and the like. It’s just needlessly injurious. It’s not a good way to practice good technique. It’s much easier, much more comfortable to get them used to high repetitions first and then start lifting heavier. As they progress as lifters, they get better muscular control, their technique improves, and they also start benefiting more from these higher training intensities. And then the training intensity depends in large part on your preference for strength versus size. If you want to maximize strength development, then for the exercises that you want to maximize strength development in, you will need to use very heavy weights. And if you really want to maximize strength development, I think there is no substitute for 1RM attempts, even. You don’t have to do them often, but you should probably do them sometimes and you should spend a considerable portion of your training in the 1 to 5 rep range. Now this comes with the trade off of having to do multiple sets and having to do very long workouts.

If you still want to get your optimum volume in for muscle growth. It might also be problematic for your joints because getting in tons and tons of super heavy sets like squats, 1 to 5 rep range, super high set volume, super heavy weights is going to take a toll on your joints, say for deadlifts, bench presses… Pretty much any exercise honestly that you do with high volume and high intensity is going to take its toll. So for a lot of people that is simply a practical concern that you have to navigate and that will go into a whole different video of injury management and the like. Suffice to say here, for maximum strength development, you will need to spend a considerable portion of your time in the 1 to 5 rep range. For muscle hypertrophy. It’s more important to maximize the total number of sets that you can do without burning out, without getting injured, etc.

That’s why we see in practice there is a difference between people that train more for strength versus people that train more for size, even though theoretically strength and size are perfectly synergistic, there is zero inherent negative interaction or any mutual exclusivity between muscle strength and muscle size. In fact, muscle size improves not just size, but also strength in a linear fashion, as we discussed in this video. And strength development might also benefit muscle hypertrophy in the long run if it increases your ability to activate muscle fibers and results in higher levels of voluntary muscle activity, which might increase your long term ability to put tension on your muscle fibers. Again, also a subject of another video. But suffice to say here, there is, for muscle hypertrophy purposes, an optimal number of total sets. Now, in many cases it seems to be the case that more is better, but not in all studies.

There are actually studies that find that higher volumes result in worse muscle growth and strength development, and we deem that’s typically overreaching or over training, and that’s given in large part by recovery capacity. A lot of factors. That’s all subjects that I’m going to discuss in other videos because this video is long enough. And that would definitely become it’s own video. The effect of, for example, cutting versus bulking, recovery capacity, men vs women. There are a lot of factors that determine the optimum to provide you with some ballpark figure that we see in these big meta analysis. The best meta analysis is actually, I think is not one of the two new ones, but is a one from 2022 by Baz-Valle et al. They found that the optimum volume in general on average is between 10 and 30 sets per muscle group per week. That’s a big range and that’s because there is big variance between individuals and one of those factors that determines the variance, as I discussed in my video on trying to failure, is how close to failure you train.

If you were to type the trains Yates vs Mentzer style, then you are going to be earning closer to that, to the 10 than to the 30 sets per muscle group per week. Probably again, depending on your recovery capacity, in principle how trained you are, many other factors, but as a rule of thumb, you’re going to be closer to ten. And if you are not training as hard, and you have perfect recovery capacity, low stress levels, great sleep, then you’re going to be earning closer to that 30 range probably.

So I hope that gives you some ballpark figures of things to aim for in your training. And what like the big picture real fundamentals are that are important to get stronger and bigger and to optimize your training programs. if if you like this type of evidence based content, I’d be honored if you like, and subscribe. See you next time.

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About the author

Menno Henselmans

Formerly a business consultant, I've traded my company car to follow my passion in strength training. I'm now an online physique coach, scientist and international public speaker with the mission to help serious trainees master their physique.

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