Chapters:
00:00 Myth #1: Direct exercises stimulate more muscle growth than indirect exercises
03:32 Myth #2: Free weights are more effective for muscle growth
04:54 Myth #3: CNS fatigue is a serious problem
10:03 Myth #4: You can take volume from one muscle group and add it to another
12:05 Outro
Transcript:
Myth #1: Direct exercises stimulate more muscle growth than indirect exercises. This myth is actually getting more popular, and not only is it a myth, it just doesn’t make any damn sense. I think when people say this they are trying to say that certain exercises are more effective for a muscle than others. I’m not disputing that. For sure, some exercises are more effective than others, but they’re trying to categorize it in a way that doesn’t make any sense. When you contract the biceps during a curl it is the same type of contraction as the contraction of the biceps during a row. There is nothing indirect about the biceps contraction during a row. There is a demand for elbow flexion, so the elbow flexors contract. There is nothing indirect about it. Some people seem to use the term “direct” refer to isolation exercises or single joint exercises, and the term “indirect” for the contribution of muscles that are involved in a compound exercise or a multi-joint exercise. Even then, this is still a myth.
A 2023. meta-analysis has looked at all studies comparing exercises for a single-joint versus exercises from multi-joints, that roughly corresponds to isolation exercises versus compound exercises, and they concluded that there is no difference in muscle growth between the exercise categories in general. Now, you might feel a muscle more and you might be able to focus on it more during an isolation exercise, but that doesn’t make it more effective, research is quite clear on this. A good example of this is the hip thrust, which many people regard as an isolation exercise, but it is actually a multi-joint exercise, and there was significant growth in the quadriceps as well. The quadriceps get recruited quite a lot during a hip thrust.
Researchers also looked at what happens when you step further away during a hip thrust, So you don’t tuck your legs as much. When you move your feet further outward, further away, it becomes more of a hip extension, a straight leg hip extension, a weird one on the floor, and then you increase the activity in the hamstrings. If you tuck your feet more, so you put your feet very close together, then you activate the quads more. You can also feel this and it doesn’t make any difference for the glutes. The glutes do the same job either with the quads or more with the hamstrings, but for the glutes it doesn’t make any difference. The body is not so inefficient that just because you are also contracting another muscle that one muscle group cannot contract to its full potential. No. Whether you contract other muscles at the same time or not does not affect how one muscle contracts. Now, as I said, that doesn’t mean that all exercises are equally effective. It’s just that, because it’s a compound or a multi-joint exercise per se doesn’t matter.
However, certain exercises are worse than others. Therefore, what I’ve always thought my students is to count fractional volumes. So you count, for example, dumbbell rows as 50% volume towards your biceps. You can say it’s partial volume, you can say they’re not fully stimulated, but it’s not indirect volume. There’s nothing indirect about it. And a new 2024. meta-analysis confirms that it is more effective to count your volume fractionally. So you count exercises that are really good for a muscle group fully and other exercises which do involve that muscle group, but they don’t let it fully contract, the force output is not maximal, like the biceps during dumbbell rows, these exercises should be counted fractionally, so you can count them as half or even less if you want to get really crazy with the fractional numbers. And this analysis found that the relationship between volume and muscle growth was significantly stronger when you count fractional volumes than when you only count direct volume, or when you count all exercises as equal. So, if you want to be meticulous with your program design you should count exercises as fractional volumes. Every exercise has a certain degree of contribution to a certain muscle group.
Myth #2: Free weights are more effective for muscle growth. than machines. Or vice versa. I’ve heard this myth go both ways. The reality is that it doesn’t make a difference. Your muscles don’t care why they are contracting. They only care what the degree of contraction is, that’s the degree of mechanical tension that will stimulate the anabolic signaling cascade, and that is what ultimately determines how much muscle growth there is. It’s just the degree of contraction, how much force output is needed during this particular movement. Whether your doing that movement in a machine, or whether you’re doing it with dumbbells, or barbells, or a kettlebell, or your mom, it doesn’t matter. We have multiple studies comparing machine and free weight exercises that are otherwise very similar, and the results are clear.
A 2021. meta-analysis concluded that free weights and machines are, on average, equally effective for muscle growth. For example, the pulldown machine is great and research finds that, even for the biceps pull downs are highly effective, which is a good illustration of both myths. Despite it being a machine it’s actually very effective, and despite it being a compound multi-joint exercise it’s still effective for the biceps. And in case you’re arguing that pull downs are not a machine because there is sufficient freedom of movement, rest assured, multiple studies have looked at actually fixed motion machine as well, and again concluded that there is no difference in muscle growth between a fixed movement pattern and a free movement pattern, as long as it’s roughly the same movement pattern involving the same musculature to the same degree.
Myth #3: CNS fatigue is a serious problem that causes prolonged and central fatigue, reducing performance in the entire body for long periods of time. Honestly, it was difficult to even put this myth into a single sentence because almost everything related to CNS fatigue is a complete myth. Whenever you hear the word “CNS fatigue” you can just replace it with “mental fatigue” or “exhaustion”, or “I feel tired” and it’s probably more accurate. Let’s look at the facts. Central fatigue in general is exceptionally rare. Yes, you get tired from lifting, but whatever you do with your biceps does not affect the neuromuscular behavior of the quads, or vice versa.
Muscle fatigue is a local process. Muscle growth, everything related to it is locally regulated. There is almost no systemic contribution. So you can do any type of training for your triceps, for example, and it’s not going to affect how your hamstrings respond to training or how much force they can produce. Researchers looked at this extensively, and according to multiple studies there is essentially no central contribution to fatigue in strength training. One study concluded: “The force behavior commonly attributed to central fatigue could be explained solely by peripheral factors and questions the very need for the existence of central fatigue.” Another systematic review and meta-analysis of 52 studies concluded: “Overall, the findings do not support the existence of a general non-local muscle fatigue effect. However, when examining specific types of performance outcomes, there may be an effect specifically upon endurance-based outcomes.”
This is a consistent finding in the literature which completely runs counter to the idea that high intensity lifting causes central fatigue, it’s actually the other way around. Endurance training does cause central fatigue. Central fatigue is not caused by heavy lifting. High intensity training has actually a very, very low effect on central and CNS fatigue. In general, the fatigue from high intensity lifting is much lower than that of low intensity lifting. If you logically think about it, how fatigued are you after a 3 rep max? Well, you cannot lift your 3 rep max anymore. However, how fatigued are you after a 20 rep max? Well, you’re so fatigued that you cannot lift your 20 rep max anymore, let alone your 3 rep max. So clearly, you are more fatigued. It also corresponds with the amount of total work done. You do much more work in a high-rep set and fatigue strongly corresponds with total work done. The muscle has simply generated more force expended more energy, and therefore accumulates more fatigue. Yes, this includes deadlifts. Research has specifically looked at the power lifts as well and concluded that they don’t significantly differ from other exercises in how much neuromuscular fatigue they generate. What they do is they demand a lot of technique.
Many people put a lot of their personal pride and effort into it compared to other exercises, so to give it more effort, they’re more anxious about doing it, it is harder to do them, it costs more mental concentration and you’re just training a big part of your body, all of that causes mental exhaustion. Mental fatigue, not CNS fatigue. There is some component of CNS fatigue, but actually this component, ironically, is almost entirely local. CNS fatigue is called Central Nervous System fatigue, but the part of the central nervous system that is fatigued is actually related to the motor neurons which are in the peripheral nervous system. So it is not central fatigue. The fatigue only affects muscle groups innervated by that motor neuron, which is usually not even a whole muscle groups, but muscle fibers. So the fatigue is extremely local.
At this point, you may be thinking: “Menno, that doesn’t make any sense. Why is it called central nervous system fatigue if it doesn’t cause central fatigue?” The reason is that the body of the motor neuron lies in the central nervous system. So technically it is part of the central nervous system. It’s part of the spinal cord. So you have the brain and the nervous system, and it extends down the spinal cord and the motor neuron originates there. So the body of the motor neuron is technically in the CNS. However it’s axon, like the tentacles, they extend outwards. And that’s where they reach the muscle fibers that they innervate, and that’s where the fatigue effect actually occurs. Because the effect of the motor neuron is only in the innervated muscle fibers. So yes, central nervous system fatigue, by and large, is actually local fatigue. There’s a big difference between “central fatigue” and “central nervous system fatigue”. Most “central nervous system fatigue” is not “central fatigue”. Most “central fatigue”, what people often call CNS fatigue is simply mental fatigue. They just feel tired. And it has very little neuromuscular contribution actually. You can get tired from doing anything that you don’t like.
Anything that is effortful causes mental fatigue. If you have to go to some family events, for example, you spend the whole day there and you have to play nice, that’s effortful and something you don’t like doing, it causes a lot of fatigue. Commuting for a lot of people also causes a lot of fatigue, because it’s something you don’t like doing. So whenever somebody talks about CNS fatigue, by and large, you can simply replace it with “it makes me tired.” Now, that is a real concern for some people. Like some people, if you don’t have the motivation anymore to continue workouts beyond a certain point and therefore you don’t give it maximal effort, and that causes you to have worse performance, then that can be a real consideration. However, this is not CNS fatigue, and it’s more related to motivation and willpower rather than any neuromuscular effect. And for most people, actually, when you measure their performance you see that it doesn’t go down. Like, their rate of perceived exertion can go up, it may feel more effortful to do that last set, but your actual performance will be the same as if you did that set earlier in the workout.
Myth #4: You can take volume from one muscle group and add it to another. A common example that guys like to do is take volume from the lower body, and add some more to the upper body. If you are not at your maximum adaptable volume yet, then adding more volume to a muscle group will increase your gains. However, the idea that you take it away from somewhere and therefore you can add more to another muscle group doesn’t make any sense. Muscle growth and fatigue are, by and large, local processes, almost exclusively local processes. They are locally regulated, research is very clear on this, stimulated by the local mechanical tension imposed on that muscle fiber specifically, and both fatigue and muscle growth are regulated by the contraction of a specific muscle that causes both the fatigue and the mechanical tension that causes muscle growth. So your upper body cannot handle more volume when you take lower body volume away. In fact there are a couple studies that show that training the lower body improves upper body gains as well. And these effects seem to be mediated by hormones. It’s also sometimes called “The hormone hypothesis”.
However, higher quality research has typically found that there is simply no effect, and the mechanisms also don’t make a lot of sense, which comes back to muscle growth and fatigue being locally regulated. Still, if anything, the research favors that doing more lower body volume actually might improve upper body gains. It certainly won’t improve upper body gains to take away lower body volume, unless mentally you don’t have the time or the effort, and therefore you’re limited by either willpower or time and you have to take some of that willpower or time away from the lower body to concentrate more volume to the upper body, and your upper body is not yet at its maximum adaptable volume. Only in that scenario does it make sense. But in principle, all muscles have a certain amount of volume that you can allocate to them. This muscle will grow this much when you allocate this much volume to it, and how much volume you allocate to the other muscle group doesn’t matter. This muscle grows half if you allocate this much volume to it, it grows fully if you allocate this much volume to it. You have another muscle group here, again, it’s the same thing. So there’s no interaction effect between how much you allocate to other muscle groups. Only the volume for a certain muscle group determines the gains of that specific muscle group.
All right. I hope this video helped clarify these myths for you. If you like this type of evidence based fitness content, I’d be honored if you like and subscribe.