What you’re getting yourself into
A deep dive into the science of hypertrophy, and why it proves that low rep training is the most efficient way to stack muscle.
If you asked your average gym bro how to get big arms, chances are you’d be rewarded with this:
- Do a dedicated arm day
- 3 sets of 12
- 6-8 exercises
- Short rests to keep the pump
- Sprinkling in a supersets
- Drop sets to drain out the last drops
- Make sure your arms seizing up by the end of the session
This reflects conventional bodybuilding wisdom, and they’ll always clarify it with “because Ronnie did it” for legitimacy.
And for many, a template like this can definitely eke out results. Especially for beginners, genetic anomalies, or those who’ve decided to plug a little extra tren into the mix. But there’ll be legions of dedicated lifters that get treated to pitiful results.
Because it’ll be way more volume than they can handle, no guarantee of quality growth reps, and the assurance of a truckload of fatigue that will diminish any growth stimulus.
Saying “Ronnie did it” is not good enough proof that it works.
More volume does not mean more growth, and it often means the opposite. I have long been an advocate for low volume, high intensity training for maximising muscle growth. It is ruthlessly efficient, where virtually every rep produces a growth stimulus.
- No dedicated arm days
- 2 working sets of 4-6 reps
- 4-5 exercises
- 2-3 minute rests
- No supersets
- Minimal dropsets
- Training to within a rep of failure
- The pump is irrelevant, progressing the weight is all that matters
This might look like it’s designed for a powerlifter. And it will definitely create serious jumps in strength. But this in fact, written with hypertrophy first in mind. In this article, I’m going to explain the science underpinning what I call low volume powerbuilding.
Is There An Optimal Hypertrophy Programme?
All roads lead to Rome, but some of them will get you there much quicker.
In a day and age where information is no longer power, we’ve all been guilty of being carried off by a Cinderella story for optimal health. There are likely a million different diets out there at this point, and a million more still need to be invented so we can each find the perfect fit for our unique metabolic woes, physical needs, and cultural palettes.
But the fundamentals of what makes a good diet are actually incredibly simple, and our free roaming ancestors didn’t have the luxury of ordering DNA and food intolerance tests so they could eat according to their special genetic configuration and microbiome.
Just like any other species on this planet, we have an optimal diet, and it’s the one we evolved to eat. Fatty red meat, a smattering of other animal products, and little else. That’s the cliff notes of what makes carnivore so potent at metabolic revival.
Obviously, to call carnivore the optimal human diet is incredibly controversial and emotionally charged, which is why I’ve dedicated many articles on this blog towards the science behind steak on steak.
For many, just the notion of starting the day with smashed burgers instead of a bowl of oats leaves them scrambling as reality splinters around them.
Now try telling the same people that saturated fat is actually healthy, and plant fats are unhealthy.
Carnivore is an outright rejection of what people grew assuming was “settled science”. It’s inevitable that there will be some blowback.
As it happens, the diet isn’t the only aspect of fitness that is made of shaky science. There are a few statements about building muscle that we’ve been taking for granted.
- Strength (3-5) and hypertrophy (8-15) sit on different rep ranges
- More volume builds more muscle
- Short rest periods increase hypertrophy
- Muscle is torn down and built back bigger
These snippets of gospel are anything but accurate, and much of it is based on the faulty premise that there are three drivers of hypertrophy.
Mechanical tension – When the muscle has to maximally contract under an intense load
Metabolic stress – The accumulation of metabolites during high rep sets
Muscle damage – Tearing the fibers down with eccentric loads and stretches
Weaponising these drivers would naturally require you to mix up the rep ranges, rest periods, and play around with forced reps and other intensifiers. But unfortunately for those who relish the chaos that ensues, big chunks of the session become useless when you arrive at the shattering realisation that two of those drivers have no effect on hypertrophy.
Does Mechanical Tension Produce Hypertrophy?
During strength training, muscle fibers experience stretching forces when they attempt to contract, but encounter resistance. This is the essence of what mechanical tension is, and the levels needed to precipitate muscle growth are reached when the reps involuntarily slow down during high effort lifts that maximally recruit the muscle fibers.
This allows the most actin-myosin cross bridges to form at the same time in the muscle fiber, enabling each muscle fiber to exert high degrees of force.
So mechanical tension is not just a case of recruiting all your muscle fibers at once, because you achieve maximal recruitment by hurling a medicine ball against a wall. Naturally, you shouldn’t be expecting to get giant shoulders just by doing such an exercise, and you won’t. Because you still need to pair maximal motor recruitment with involuntary slow contractions. This is known as the force-velocity relationship.
In practice, these growth reps occur on the last 4-5 reps from failure, regardless of whether you’re lifting a 5 rep max (RM) or a 15RM. Why can we be so specific?
For one, we know that full motor recruitment is achieved in most muscles at 85% of 1RM, which equates to a 5RM.
A study by Haun in 2018 showed well-trained athletes experiencing minimal hypertrophy while training at 4 reps in reserve (RIR). This was despite using extremely high volumes, at 32 sets per week.
Another study from 2021 compared lifters training to failure, to another group that stopped 5 reps short of failure. The former saw significant hypertrophy, while the latter saw virtually no improvements.
These results show that the last 4 reps from failure are critical for maximising hypertrophy.
It’s easy to gauge for yourself whether you’ve reached mechanical tension. If you jump on the bench and load it up with your 8 rep max, you’d see the concentric portion of your reps start to slow down around the third or fourth rep.
If you were to attempt the same lift with your 5 rep max, and take it to failure, then every concentric rep is going to be nerfed despite your best efforts.
This slowdown is further backed up by study showing that an exercise that was stopped after reaching 40% velocity loss resulted in much greater hypertrophy that one stopped at 20%.
It’s worth dispensing with a few ways you might misinterpret the science of mechanical tension.
Mechanical tension does not happen when you lift the bar deliberately slowly, since that prevents you from activating the high threshold motor units that are needed for full recruitment.
It also does not exclusively happen with heavy weights, which has been a myth perpetuated by strength coaches. Any set taken to failure will eventually require the maximal motor recruitment and involuntary slow contractions. So a set of 15 reps to failure may be routine at first, but eventually you’ll grind it out to the point where the muscle has to start fighting tooth and nail.
This is backed up by a study from 2019 showing that, despite using different loads, bar speed was the same at a set number of reps from failure.
This is worth repeating again. There is no rep range for hypertrophy. 4-6 and 10-15 can both trigger the same amount of hypertrophy as long as training to failure is assured.
Naturally, the body adapts, and yesterday’s load on the bar becomes less of a challenge, and less likely to create sufficient mechanical tension. So you either progress the reps or the weight to continue to get the same stimulus.
But this does not mean that low reps and high reps are both optimal for hypertrophy, nor does it mean that you should always train to failure in order to maximise the growth reps. There are confounders, as we’ll soon get into.
But before we do that, allow me to disavow the two red herrings of hypertrophy.
Does Metabolic Stress Produce Hypertrophy?
This potential driver can also go by the names “metabolic fatigue”, “sarcoplasmic hypertrophy” and “the pump”. The base logic here is the metabolites built up during weight training have their own independent effect on muscle growth.
These metabolites can be increased by doing the following:
- Increasing reps
- Increasing sets
- Increasing volume (weight x sets x reps)
- Training closer to failure
- Not locking out reps
- Shortening rest periods
- Adding supersets, dropsets, and other set extenders
Naturally, metabolic stress is the driver used for the high volume crusade, and there are plenty of studies suggesting that more volume does lead to more muscle growth. But despite the lofty status that metabolites enjoy in many coaching manuals, we still have no proof showing that they do have a direct impact.
If metabolic stress does cause hypertrophy, then inducing hypoxia in the form of blood flow restriction training (BFR) on resting muscles would show muscle growth. Except it doesn’t.
If it was the build-up of lactate that was working the magic, then a lactate infusion would result in muscle growth. And it doesn’t.
In case you’re not convinced yet, there are also plenty of studies showing that long rest intervals vastly outperform short rests in both strength and hypertrophy. Despite the fact that short rests would inevitably increase metabolic stress.
I’m sorry to say this, because I know it’s going to be a sore one, but the pump has nothing to do with building muscle. It’s just a fun side effect that often comes along for the ride.
Does Muscle Damage Produce Hypertrophy?
This is the idea that muscles are torn down and built back bigger. Lifters then naturally take it to heart by brutalising their bodies on the gym floor, then defining their progress by the challenge of getting up from the toilet the next day.
Muscle damage can be caused by the following:
- Increasing reps
- Lengthening eccentrics
- Increasing load on eccentrics
- Stretching
- Training to failure
Once again, science doesn’t jive with this mechanism. For one thing, muscles are not torn down and built back bigger. There’s no tearing taking place when you’re lifting, unless you want to end your session in a hospital. Muscle damage is the degradation of proteins, and it doesn’t cause those proteins to be stacked up any higher or thicker.
We do see an elevation of muscle protein synthesis as a consequence of muscle damage, but that simply signals a repair process for damaged tissues. The body has to fix the muscle damage before moving onto the business of hypertrophy.
And if muscle damage was an independent cause of muscle growth, then muscle contusions would give up great results. But, as you might have guessed, they don’t have any effect.
To underline the lean offerings of muscle damage, one study comparing lifters that allowed or avoided muscle damage, found no discernable differences in hypertrophy.
Just like metabolic stress, muscle damage is merely a byproduct, and not the goal. In fact, chasing them can actually inhibit your goals, due to the thorny issue of fatigue.
And by tackling fatigue, I’ll be able to underline just why low volume is the safe and effective route for stacking muscle.
How Fatigue Blunts The Growth Reps
It should be clear by now that volume as we know it, the sum of weight x reps x sets, has no bearing on how much muscle is being built.
Since it’s only last 4-5 reps that stimulate muscle growth, then the relevant volume metric would be the sum of the sets taken in close proximity to failure. This is what I would call “growth volume”.
With that in mind, it may seem a straightforward take that we should simply train to failure all the time to get the best possible muscle growth. But we always need to muddy the waters with some nuance.
Fatigue, which can be peripheral or originating in the central nervous system (CNS), inhibits the amount of muscle fibers being stimulated. It is an inevitable consequence of training. CNS fatigue is particularly notable since it wastes little time stopping the high threshold motor units (HTMR) from being activated. This is an issue, because HTMRs control the muscle fibers that let you maximise muscle growth. They represent the ceiling, and you don’t really want them closed off.
To underline that issue further, CNS fatigue builds up rapidly at the beginning of a workout, which shows that first few sets of your workout will dominate in terms of stimulation.
So it stands to reason that a solid hypertrophy programme would try and minimise CNS fatigue, which is exacerbated by the following:
With the principles of growth reps and CNS fatigue in mind, we have the requisite scientific knowhow to put together the optimal programme.
The final rep from failure causes disproportionately greater levels of CNS fatigue, compared to the other stimulating reps. Which is why you’ll likely see your best performance and growth when keeping the last rep in the tank. Instead of taking your growth sets to 0 RIR, you stop at 1 RIR.
Going back to the matter of overall volume, it would be the smart play to limit the amount of junk reps, which I would use to describe any reps that aren’t growth reps. That brings us nicely to the 4-6 rep range.
The amount of growth volume you need to spike muscle growth isn’t going to be a straight line that stretches past the canopies. Past a certain amount, you won’t see any further muscle growth from a session.
If anything, exceeding that volume threshold can just result in worse results due to the effect that CNS fatigue can have on both stimulation and recovery. This can build up to a point where you’re stagnating in both strength and hypertrophy, and in dire need of a deload.
Deloads are only really necessary when you’re training with high volumes and doing too many junk reps. Otherwise CNS isn’t a major issue, and should be shuttled out in time for the next workout, so you’re not heading in with nerfed stats.
I realise this may appear in contrast to an article I’ve made on the need for deloads. But that wasn’t written with low volume training in mind.
The science supports the diminishing returns of high volume training.
One study displayed substantial hypertrophy at 3 sets per week, and needed 18 sets just to double that amount of growth.
Here is one study showing that 12 sets per muscle group showed no further growth when compared to 8.
Another comparing 6, 9, and 12 sets per workout that was qualified at 2 RIR found the best gains at 6 sets, at what we can call “low volume”.
6-8 sets per muscle group per workout is a fair estimate for the high end of growth volume. If anything, you’d be better off initially aiming for 3-5 in order to progress without running the risk of overtraining.
6-8 hard sets would be considered low volume for many gym rats who are bent on reaching complete exhaustion by the end of the session.
But if we can assure quality work on those hard sets, by which I mean long rest periods, 4-6 rep sets at 1 RIR, then chances are you can get by with less.
The Optimal Programme For Building Muscle
The objective of this article isn’t to set down an immutable collection of rules for stacking size. There’s nothing wrong with applying similar parameters with 6-8 reps. I wrote this simply to show the science behind hypertrophy, the one driver that you need to worry about, and the ways in which people tend to sabotage their training.
A good workout isn’t measured by how exhausted you are at the end of it.
What matters is whether you trained to failure, and thereby reached mechanical tension, and stimulated muscle growth.
If you can do it 4-6 reps, then you’ll be making it sustainable, and sidestepping the need for any time out.
Since 4-6 rep sets are inherently less fatiguing than 10-12 rep sets, and resting for 3 minutes is going to be much easier on your cardio than a lightning 1 minute break, you’re really making life easier for yourself.
And just as a nice bonus, you happen to be in a perfect range for building strength, meaning you really don’t have to deviate in reps regardless of your current goal. This is the essence of powerbuilding. You don’t need to choose between being strong and looking strong.
If you get more muscle growth than high volume training, and there’s a fair chance of that, then you’ll be feeling very smug.
If you get the same amount of muscle growth as high volume training, then you get there expending less effort, and smugness shouldn’t drop past 10%.
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