Author Topic: Trained lifters are primarily stronger due to muscularity not neural adaptations  (Read 14525 times)

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CoolColJ

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https://www.strongerbyscience.com/research-spotlight-muscularity/





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When we ask about the relationship between muscle growth and strength gains, we’re asking, “to what extent are strength gains influenced by ‘neural’ adaptations, and to what extent are strength gains influenced by structural (i.e., hypertrophic) adaptations?” However, most of the time when researchers investigate this question, strength is quantified, muscle size is quantified, and neural adaptations are merely assumed to “fill the gap.”

With that in mind, the presently reviewed study fills a major gap in our understanding of this topic (PMID: 34617822). Researchers recruited 16 trained (average of 5.9 years of resistance training experience) and 14 untrained men. The subjects’ maximal isometric elbow flexion strength, biceps anatomical cross-sectional area, and motor unit behavior during submaximal isometric contractions were assessed.

The results of the study were straightforward: the trained lifters were considerably stronger than the untrained lifters (64.8% greater maximal isometric elbow flexion force) and considerably more muscular than the untrained lifters (71.9% greater biceps anatomical cross-sectional area). However, motor unit behavior was similar between the groups.

The last sentence of the abstract summarizes these findings well: “The greater absolute force-generating capacity of [strength trained individuals] for the same neural input, demonstrates that morphological, rather than neural, factors are the predominant mechanism for their enhanced force generation during submaximal efforts.”

Every time I revisit this subject, I become more convinced that for healthy people without neurological conditions, muscle size really is the primary determinant of muscle contractile force, with all other factors playing much smaller roles. When you remove any technique or skill-based components from the equation, “neural” factors don’t seem to matter much: bigger muscles are stronger muscles.

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The results of the study were pretty straightforward: the trained lifters were considerably stronger than the untrained lifters (64.8% greater maximal isometric elbow flexion force) and considerably more muscular than the untrained lifters (71.9% greater biceps anatomical cross-sectional area). However, motor unit behavior was similar between the groups. Recruitment thresholds were similar (relative to maximal force), motor unit discharge rates were similar during each submaximal contraction, and the relationship between discharge rates and relative force output were all similar between groups. The last sentence of the abstract summarizes these findings quite well: “The greater absolute force-generating capacity of [strength trained individuals] for the same neural input, demonstrates that morphological, rather than neural, factors are the predominant mechanism for their enhanced force generation during submaximal efforts.”

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Every time I revisit this subject, I become more and more convinced that for healthy people without neurological conditions, muscle size really is the primary determinant of muscle contractile force, with all other factors playing much smaller roles. When you remove any technique or skill-based components from the equation (i.e., when you just assess force isometrically), “neural” factors don’t seem to matter much: bigger muscles are stronger muscles. That equation gets a little murkier once you start dealing with more complex lifts used to assess strength, but even with more complex lifts, I think “neural adaptations” should more appropriately be referred to in  less opaque terms, like “technique” and “motor skill.” In other words, if a pitcher in baseball improves their pitching mechanics over an offseason and starts controlling their pitches better, we’d probably say, “they improved their mechanics, so they’re doing a better job of hitting their spots.” We probably wouldn’t say, “they’re pitching better due to neural adaptations.” I think the same concept applies to strength: if someone can lift a ton of weight relative to the amount of muscle mass they have, I doubt it’s due to a preternatural ability to recruit more motor units, or the ability of their motor units to discharge rapidly; rather, it’s more about technique and general motor skills (and probably favorable structural factors as well). “Technique” and “motor skill” also have neural origins, of course (probably relating to adaptations in the motor cortex or cerebellum), but I don’t think those are the sorts of “neural adaptations” people have in mind when they use the phrase.
« Last Edit: March 16, 2022, 01:30:39 pm by CoolColJ »

CoolColJ

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Just for some more background information here (specifically for the people concerned about the use of curls, or people concerned about the MU measurements being performed at submaximal intensities):

First, neural adaptations aren't synonymous with technique or general motor skill. In a research context, neural adaptations are generally adaptations that affect the contractile force of a muscle per unit of input from the nervous system. For example, if you recruit more motor units at a lower relative force output, if you can achieve higher motor unit discharge rates, or if a given relative increase in motor unit discharge rates results in a greater relative increase in force output, those are all indications that neural adaptations have occurred. Technique and general motor skill, on the other hand, more-or-less refer to your ability to get everything you can out of your muscles in a more technically demanding exercise.

The current dominant thinking is that trained lifters have better technique/general motor skill than untrained lifters, and that neural adaptations have occurred, such that they achieve greater motor unit recruitment and higher discharge rates (and thus greater force output) per unit of input from the nervous system to the prime movers. However, those assumptions about neural adaptations are largely based on studies that simply assess surface EMG amplitudes, which may not actually reflect "true" neural adaptations (https://www.researchgate.net/publication/262019289_The_increase_in_surface_EMG_could_be_a_misleading_measure_of_neural_adaptation_during_the_early_gains_in_strength).

For assessing neural adaptations, movements that require minimal motor skill and technique are preferable, because you're attempting to separate performance due to neural adaptations from performance due to motor skill and technique. And, specifically, isometric contractions are preferable because they have an even smaller skill component than relatively simple dynamic contractions, and because they're necessary for actually decomposing an EMG signal using HDsEMG, in order to study the behavior of individual motor units. With dynamic movements, your muscle fibers move a bit relative to the electrodes on the skin, so you can't isolate the signals of individual motor units. Furthermore, submaximal contractions are preferable, because they let you assess motor unit recruitment thresholds over a larger range of target force outputs, and changes in motor unit discharge rates in a larger pool of motor units.

So, this study found that:

1) motor unit recruitment thresholds are the same between trained and untrained people at all intensities assessed (pushing back against the idea that trained lifters can recruit a larger proportion of MUs at submaximal forces)

2) motor unit discharge rates are the same between trained and untrained people at all intensities assessed (pushing back against the idea that trained lifters perform better by achieving higher motor unit discharge rates)

3) the relative increase in force output per unit of increase in motor unit discharge rate is the same in trained and untrained people (pushing back against the idea that trained lifters perform better by achieving larger relative increases in force output per unit of neural input)

4) the strength difference between trained and untrained individuals in a low-skill task (maximal isometric elbow flexion) was reflective of differences in elbow flexor size: ~65% difference in force output, versus ~70% difference in anatomical cross-sectional area. This suggests that there's not any neural magic occurring somewhere between the highest submaximal intensity tested (70% of maximal force) and maximal intensity; if there was, the trained lifters should have achieved greater maximal force output per unit of muscle size.

All of that strongly suggests that resistance training doesn't improve your ability to recruit motor units, achieve higher motor unit discharge rates, or squeeze more force out of your muscles per unit of motor drive in a general sense. So, when people chalk improvements in performance up to "neural adaptations," they're probably just observing improvements in general technique and motor skill with the specific tasks being assessed. The adaptations required to coordinate a complex movement (i.e. general technique and motor skill) are not the same adaptations required to increase force output per unit of neural input. I do suspect that, say, hamstrings MU recruitment increases as someone gets more experience with deadlifts, but that's reflective of improvements in technique and motor skill, not the nervous system's inherent ability to recruit MUs in the hamstrings or achieve high MU discharge rates.

FP

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This is a good read and an interesting approach to study, using Iso's. Knowing that discharge rates and mu amount recruitment doesnt change between trained and untrained lifters is so theoretically helpful, knowing that those are not qualities that are being developed. It sucks they cant use dynamic movements though, not sure if its a good idea to try to argue that dynamic movements work the same way, that would be interesting to know

But i want to add on a point (that doesnt contradict the study in any way), and i suppose its pretty well known, that during dynamic movements, the GTO is super overprotective and limits force output to 40% or less. (I learned this from Triphasic Training) And training over long periods improves this quality. I suppose that would be part of the movement skill. I dont know how much thats a factor for less complex movements.But I guess through this you could argue that movement skill and neural factors are inseparably linked for most activities.

So when they say:
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All of that strongly suggests that resistance training doesn't improve your ability to recruit motor units, achieve higher motor unit discharge rates, or squeeze more force out of your muscles per unit of motor drive in a general sens
I guess it depends how you interpret that, but what worries me is the way it is worded people might draw more extreme conclusions not taking that GTO factor into account and might choose to do BB instead of PL. Like basically in terms of practical conclusions, I dont see how this study should affect anything.

Also theres sarcoplamic (or sarcomere? I dont remember) hypertrophy to account for where some types of training add functionless mass (I learned this from skimming Supertraining). So those ratios could be a little different if one could account for that but since they have like 30 people involved maybe this has less of an effect because for some or most of them thats less of an influence.


CoolColJ

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Sarcoplasmic hypertrophy would refer to the non contractile elements of a muscle like the capillaries, water bloat, and other tissue.
It's proven to be a non factor as it doesn't occur to any great extent, unless your pro bodybuilder pumping himself/herself with a ton of drugs.

It's hard enough for a natural trainee to gain any sort of hypertrophy in the short term to have to worry about any of that  :strong:

A few more quotes from Greg Nuckols in responce to comments

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    It does, however, imply that a trainee should not move beyond more fundamental, hypertrophy-based training if they have no intention of competing / testing any time soon.

I largely agree with that. I do think there's value in mixing in some heavier training just to maintain/improve skill with heavier loads, but most of your training should include enough volume to provide a solid hypertrophy stimulus.
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They were trained males, not specifically powerlifters. I'd wager that curls are EASILY one of the most-performed exercises among resistance-trained males.

    They would likely have poorer bicep MU recruitment with an isolated isometric than they would with a compound

Nah. MU recruitment is essentially maximal in single-joint lifts. You can see that in studies that assess voluntary activation. Subject produce as much force as possible isometrically, and then electrodes zap the motor nerve (while the subject is still exerting maximal force) to ensure that every MU is firing. If the zap increases force output quite a bit, that suggests that the subject wasn't achieving maximal MU recruitment. In studies on young folks without neurological or serious orthopedic conditions, voluntary activation is essentially 100%
« Last Edit: March 18, 2022, 06:56:06 am by CoolColJ »

FP

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Hmm about the functionless mass, i will have to look at more info on that but your view is valuable. My guess is it would be tough to measure.

 I guess for me training for an athlete PL has always been much more practical because presumably traditional BB builds mostly slow twitch. But I guess for some reason Im also assuming that PL trains GTO more than BB. Which kind of makes sense (although im not sure thats right) because with PL you are supposed to be explosive all the way throughout, and if every rep is attempting to max out the motor pool, you are trying to break through the limits set by GTO. Also using higher weights would presumably do this.

But all I have written down about this though is that ballistic and dynamic stretches help inhibit GTO and eccentric training also inhibit GTO. But this might mean a short term inhibition because you are proving to your body it can handle stuff safely. Gotta look into this a little more too

CoolColJ

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Yeah, Powerlifters lift heavy for the actual skill component of their sport
But you will also find the rest of time they do high volume hypertrophy work

So athletes lift to increase strength and improve injury resistance.
And if strength and relative strength is largely due to getting bigger in the relevant muscles and just being lean.
Then that simplifies programming a whole lot



Dreyth

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Somewhere deep in my logs my 1RM squat dropped from 415 to 335 i believe in a matter of 1-2 weeks. I had only take a few days off from lifting i think. I dont recall any drastic sleep or stress changes during that time. How does that factor in here?

Through my decade of squatting, many ups and downs, i’ve definitely noticed i gain the most on high frequency (85% max 3x a week, with 1 of the days being a “light day” working up to a 85-90% single and no work sets) and i attributed some of my success to neural adaptations (whatever they may be). Im wondering how my n=1 experience fits into the information from this thread
I'm LAKERS from The Vertical Summit

CoolColJ

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Somewhere deep in my logs my 1RM squat dropped from 415 to 335 i believe in a matter of 1-2 weeks. I had only take a few days off from lifting i think. I dont recall any drastic sleep or stress changes during that time. How does that factor in here?

Through my decade of squatting, many ups and downs, i’ve definitely noticed i gain the most on high frequency (85% max 3x a week, with 1 of the days being a “light day” working up to a 85-90% single and no work sets) and i attributed some of my success to neural adaptations (whatever they may be). Im wondering how my n=1 experience fits into the information from this thread


Strength display is a summation of many factors on any given day - your brain still has to send that electrical signal to many muscles in the proper order, rate, timing etc.
the strength of the signal is not a constant thing, it varies depending on the state of the body, but when the muscles get it, they all fire on or off.

Austin Baracki of Barbell medicine has a few good posts on this

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182.5 kg / 402 lb x 3 (17 lb PR)
BW 193

We want to think we can control a lot more than we really can.

This is 40 lbs heavier than the same set of 3 from last week … which was 20 lbs less than the week before … which happened to be a 5 lb PR triple at the time.

Nothing about my programming changed this time, nor have there been significant changes to my bench training for the past 4-6 months. No low stress / deload / pivot weeks, no changes to exercise selection or volume.

So, where did these PRs come from? I don’t know. They just happened from adjusting loading to match day-to-day performance, known as “autoregulation”, until the stars aligned today 🤷‍♂️

We think by planning out our training cycles in advance, sometimes pre-selecting our loads for the next 12 weeks, or by adjusting the minutiae of training variables that we can produce reliable training responses over time.

This is why lots of folks maintain meticulous training logs, review data, and pro-actively plan things like block lengths, deloads, and sequences of exercises based on their past responses.

I wish we were all robots that responded to training inputs this predictably. Unfortunately, human lives are way too complex for these things to reliably reproduce over time.

Additionally, the pace of adaptation (and thus performance) is heavily influenced by things outside of our control, and tends to happen on its own timeline. The things that we control the most, whether you do sets of 3 or sets of 5, whether you add 5 lbs or not on a given day, or whether you do a paused or a pin squat, probably matter the least in the big picture.

Expecting to plan and time specific adaptations in advance is often a road to frustration, burnout, or injury. Instead, try

1) finding a reasonable, sustainable, and enjoyable training setup
2) matching loading to day-to-day performance using an autoregulation strategy
3) accepting the process of doing this consistently for years and years on end

With these in place, results are going to happen on their own timeline. There will be plenty of ups and downs - the challenge is finding ways to enjoy, and stay on, the ride.