Updated: Oct 6, 2018
It is commonly believed that, to grow, muscles need activation mostly in the 8-12 rep range – between the ‘strength’ and ‘endurance’ rep ranges, with rest periods between 45 seconds and two minutes. Not so low in reps and high in intensity to be considered strength and not so high in reps and low in intensity to be considered endurance. The Goldilocks of resistance training, the just-right, middle way of lifting.
In reality, however, the optimal rep range and training intensity for maximal muscle growth varies from individual to individual (and even from muscle group to muscle group within each individual), is not likely to be in the 8-12 rep range for at least half the population, and can be made more accurate than a range (rather a single number, as a rep target).
Some preliminary understanding - forgive me if you already knew all this
Training intensity in exercise science is defined as a percentage of one repetition maximum, which should be distinguished from training intensiveness - a subjective measure of how effortful a workout or exercise is. For example, if your one rep max on bench press is 100kg and you want to use an 80% training intensity, then you would be working with 80kg, regardless of how effortful you find that.
Although hypertrophy is said to be the middle ground between endurance training and strength training, it more closely resembles strength training; with rep ranges and generally longer rest periods that are closer to those used by strength trainees, being more optimal for muscle mass gain, compared to those used by endurance trainees.
The difference between pure strength training and hypertrophy training is that, for strength you want to get stronger at a specific rep range, ie your one rep max (you simply want to increase the maximum load you can lift for one rep only); and all training is directed toward that goal alone.
Whereas for hypertrophy training you want to get stronger in whatever rep range you can get stronger fastest at for each exercise, regardless of where on the strength-endurance spectrum that may be.
Generally the more developed you become as a strength trainee, the higher overall training volume (total Sets X Reps), and the higher training intensity (heavier weights), you will need for continued muscle growth. The higher training intensity you use, however, the fewer reps you will be able to perform in each set, reducing the overall volume. You can increase the set-volume (number of sets per body part per week) in order to increase the overall training volume but only up to a point, at which more sets become less optimal because recovery is impeded. Thus finding the right balance between training intensity and overall training volume is key to optimal hypertrophy training, and the essence of this article.
The combination of training intensity and set-volume that achieves the fastest progress in each individual, for each exercise, is what I call the ‘hypertrophy sweet spot’. It varies from individual to individual, and from muscle group to muscle group, and changes as you progress as a lifter. If you find your personal hypertrophy sweet spot in each muscle group and stay with it as you progress, you should achieve some strength development in each lift, in every session.
Determining your personal hypertrophy sweet spot
It is relatively easy to achieve some muscle growth with any kind of resistance training at the start of your strength development journey; you just need to be hitting the dart board at this point. Or even just pointing in the right direction. Completely sedentary individuals can even increase their one repetition max in the back squat simply by endurance bicycle training. Of course this is not to say that progress in beginners can be maximized with the use of any form of resistance training - there are still a particular set of stimuli that beginners will progress fastest at, gaining more muscle mass and increased strength development compared to other stimuli, but it is fairly easy to achieve some progress at this stage.
As your body adapts to the training, however, it requires that you become more and more accurate in hitting this sweet spot to cause continual muscle growth and strength development. And what was once your sweet spot as a beginner will no longer be the same as you progress toward being an intermediate lifter. The target moves and as well as becoming effectively smaller and smaller. It moves towards the ‘strength’-end of the spectrum, away from the ‘endurance’-end, as you progress, meaning that you will require a higher training intensity, using lower rep ranges, to continue progressing, the more developed you get.
Hitting this moving, diminishing target becomes increasingly difficult once you break into the category of an intermediate level lifter, making the jump from intermediate to advanced, especially difficult. Unfortunately, because of all the misguided information and lack of knowledge in the fitness industry out there, many trainees do not achieve the accuracy in their training required to make the jump from intermediate to advanced; they plateau and just accept that this is the end of their gains and strength development.
It doesn’t have to be! If you find your sweet spot in each muscle group you can continue getting stronger and more muscular week by week, all the way into the deep end of an advanced level or even elite level lifter. You can even continue getting stronger, while losing body fat at the same time if you train accurately enough and provided nutrition and other lifestyle factors are also in check (you can’t train with 100% accuracy and then pull a three-day intoxicant-fuelled weekend, eat a pizza at the end of it and still expect to progress just because you trained good three days ago – your recovery conditions need to be at least good enough, probably should be optimised and may require fine tuning, depending on how advanced you are).
For many lifters the broad-stroke advice to use 8-12 reps for hypertrophy begins to become less than optimal once they reach the intermediate level. Granted there will be those who do still progress in this rep range all the way into the advanced category as this may well align well enough with their particular hypertrophy sweet spot, while they are at the intermediate level, however this will not be the same sweet spot for many other intermediate level lifters. Even so, these said lifters would still benefit to figure out exactly where in the 8-12 rep range they progress fastest at, for each exercise, be it 8, 9, 10, 11 or 12 reps. It may well be that for one person 8 reps is the optimal intensity for one exercise, and 12 reps is the optimal intensity for the same person in another exercise. Figuring this out exactly can increase the rate of progress in each exercise, and resultant muscle mass gained, significantly.
To better understand the categorisation of levels of advancement of strength trainees, look at this chart.
Finding an individual’s hypertrophy sweet spot depends mainly on three things:
Your personal composition of muscle fiber type, in each muscle group
Your likely genetic potential (The maximum amount of muscle you could theoretically gain in your lifetime based on your genes; largely your bone structure)
How close you currently are to your genetic potential (How advanced a lifter you are)
Fiber type composition
There are three different muscle type fibers: type I (slow), type IIa (fast) and type IIb(fast). Type I fibers contract the slowest, are the most efficient in their energy use, produce the least force and fatigue the slowest. They are your long distance marathon-running endurance fibers. Type IIa contract faster, are less efficient in their energy use, less resistant to fatigue, and produce more force. Type IIb contract faster still, are the least efficient in their energy use, fatigue the quickest and produce the most force. Type IIb are your 100m sprint, one rep max strength fibers, with Type IIa falling in between type I and type IIb, but closer to type IIb.
If you are reading this article then you probably already knew that, so I won’t bore you further by explaining how they each use different fuel sources or talk about ATP, phosphocreatine and the krebs cycle. What you do need to know, however, is that muscle fiber type composition varies from individual to individual and within each individual, from muscle group to muscle group. This in turn affects how many reps you can perform at a given intensity of one repetition max for each exercise and is therefore relevant in figuring out your personal hypertrophy sweet spot.
Type II fibers can grow much larger, and also grow faster than type I fibers, and thus are more relevant to hypertrophy training (this is why hypertrophy training more closely resembles strength training than it does endurance training). You do still want maximal hypertrophy across all fibers, however, not just type II fibers, although an emphasis on type II is more effective for muscle mass gain.
Different muscle groups have different fiber type compositions according to their evolutionary needs. Calves, for example, are more slow-twitch dominant because they are needed to help us in standing up straight and for walking; low output long duration endurance exercises that we used to do a lot of. Triceps on the other hand are more fast-twitch dominant, possibly because they are used for striking, and throwing, activities that require a high force-output in short bursts. This article, by Menno Henselmans goes into the detail of fiber type composition in each muscle group.
There is a minor genetic difference in fiber type composition from person to person and a comparatively large difference between each different muscle group, in everyone. Still, the minor difference in fiber type composition between individuals is enough to make for different optimal training parameters for each individual. Generally speaking, while people will have similar optimal rep ranges (although there are the outliers) for the same exercises at the same level of strength advancement, people who are slightly more fast-twitch dominant, for example, will do significantly better at a slightly lower rep range . This makes using an appropriate rep range according to your personal fiber type composition highly effective.
While it is extraordinarily difficult to figure out exactly an individual’s fiber type composition in each muscle group, without a biopsy, there is a practical method to determine an individual’s optimal rep target for each exercise, which takes fiber type composition into account, which I will explain later in the application section of this article.
Take home messages:
Optimal training intensity and volume depends on muscle fiber-type composition and is likely to vary from muscle group to muscle group in each individual
If you are more fast-twitch dominant in any particular muscle group, then you will likely do better at a lower rep range using heavier weights in exercises related to that muscle group.
If you are more slow-twitch dominant in any particular muscle group, then you will likely do better at a higher rep range using lighter weights in exercises related to that muscle group.
It is sometimes glossed over by personal trainers, but your potential for muscle gain is indeed, largely genetically determined. This does not mean that you either can or cannot get ripped and muscular or toned - anyone can get in shape, but there are those who can get in shape with relative ease, and who are likely to become the record setters in the strength sports, and for everyone else it requires varying degrees of difficulty. Whether you are better designed for strength sports or not should not be seen as a consideration in deciding whether or not you should invest the time and energy to get the most out of your body that you can - you should regardless, it will be worth it.
Understanding your genetic potential is important in determining your training variables because to accurately calculate your optimal training parameters you need to know how strong and muscle bound you are relative to your own potential. If you are incredibly strong but nowhere near your full potential yet, then for practical programming purposes you may well only be a novice, and should use rep targets and set-volumes appropriate for a novice as this will see you progressing the fastest. Whereas if you have been training accurately for many years but have comparatively modest strength, you may be quite close to your genetic potential in which case it is better fitting for you to train as an advanced or elite level lifter, because in terms of your own potential you are advanced or elite, even if there are intermediate level lifters with a higher ceiling for maximum muscle mass, lifting more than you.
It is also possible to have different genetic potential in different body parts and to be in varying levels of advancement, relative to your own potential, in different body parts. For example you may have better than average potential in your lower body and slightly lower than average potential in your upper body. Or even, better potential in your chest than in your back. And you may be more advanced relative to your potential in one body part than you are in another. Remember you also may have varying fiber type compositions in different parts of your body meaning you will do better at a different rep range than someone else with the same bone structure, body weight, muscle mass and level of advancement as you. Human bodies are extraordinarily complex, each one is completely unique and needs a particular set of training stimuli to grow optimally.
Figuring out your likely genetic potential for building muscle mass is somewhat of an estimation as there are no scientifically reliable, accurate methods, yet, to do it. One especially telling variable is frame size. The larger your frame, the more total muscle mass you can build [1, 2], and the quicker you can build it. A helpful objective measurement of frame size is wrist and ankle circumferences relative to height. Data from the US Libray of Medicine can used as a reference.
Another objective measure to help determine genetic potential is the 2D:4D digit ratio, in the right hand. The 2D:4D ratio is an indicator of pre-natal testosterone exposure, which impacts one’s genetic potential for muscle mass. If you have a low 2D:4D digit ratio (ie, your ring finger is longer than your index finger, in men, or of equal lengths, in women) this is an indication of better genetic potential for strength development and muscle mass gain.
An individual’s birth weight is also a somewhat reliable measure for predicting genetic muscular potential; heavy babies tend to have better genetic muscular potential. (The average Caucasian new born weighs 3.4kg)
Racial phenotype is another, and can be distinguished in the following order Black > Caucasian > Asian in terms of potential for muscle mass gain.
There are also some more intuitive ways of knowing how genetically gifted an individual may be. Frame size, joint size, square-ness of jaw, size of Adams apple and deepness of voice, and amount of bodily hair (especially facial, forearm, chest and abdominal hair – in men) , are all traits that correlate well with genetic potential for muscle mass gain.
Together with the more concrete, quantifiable variables mentioned before, all of these indications help to paint a picture of how high an individual’s genetic potential for muscle mass might be. Someone with a massive frame, a hairy torso, deep voice, square jaw, large joints, a low 2D:4D digit ratio and thick wrists and ankles, is simply likely to have a higher genetic potential than someone of average size and proportions.
In practice it takes some experience working with different body types to develop a good intuition of whether someone is likely to have better or lower than average genes, to the point that it affects their characterisation as a lifter, but at least there are some concrete data to work with that anyone can use as a starting reference point, with ankle and wrist circumference, 2D:4D digit ratio, birth weight and phenotype.
For the record, I was born of average birth-weight, have a slightly lower than average 2D:4D digit ratio, have an average wrist circumference, slightly lower than average ankle circumference, and a slightly narrower-than-average jaw line. But I do train seriously, and with accuracy.
Take home messages:
Your genetics play a large role in muscle development
How genetically gifted you are or aren’t affects your maximum ceiling for muscle development (how much muscle you could theoretically gain in your life). This is relevant in determining your categorisation as a strength trainee and resultant optimal training parameters
Level of Advancement
Once you have determined your genetic potential the next step is to determine how close to your limits you already are. This can be done quite simply by comparing your strength in various lifts, at a given body weight, to recognised strength standards for the general lifting population. This chart is a good reference.
Bear in mind that these data are for the lifter of average genes. If you are genetically gifted then you need to factor that in and shift down the categories accordingly, to adjust for your likely higher potential. If your genes are lower than average then you need to shift up accordingly to adjust for your likely lower potential.
The following method can be used to determine an individual’s optimum rep target and training intensity for each exercise in their program, factoring in their unique fiber type composition and differing levels of advancement in each muscle group.
Find your one rep max in each exercise you want to use in your training program.
Finding a true 1RM can be tricky. Ever tried finding a 1RM for a dumbbell fly? You can use the Epley formula to estimate it instead, based on your 3RM for compound exercises, and 5RM for isolation exercises. This is accurate enough, but the closer you can get to your 1RM the better (1RM>2RM>3RM>4RM>5RM).
Epley Formula: Weight X (reps/30 +1)
Apply the following guidelines (source), to determine your optimal training intensity based on your one rep max:
· Novice lifters should use 60% for both isolation and compound exercises
· Intermediate lifters should use 65% for isolation and 80% for compound exercises
· Advanced lifters should use 70% for isolation and 85% for compound exercises
· Elite lifters should use 75-80% for isolation and 90%+ for compound exercises
Use the following guidelines to determine your optimal set-volume.
· Novice lifters should use a set-volume of 12-13 sets per body part, per week.
· Intermediate lifters should use a set-volume of 16-18 sets per body part, per week.
· Advanced lifters should use a set-volume of 24-28 sets per body part, per week.
· Elite lifters should use set-volume of 28-40 sets per body part, per week.
Use the training intensity determined in step two and set the weight accordingly, for each exercise.
If you cannot make the weight exact, just get as close to, as possible. Most gyms will not have increments lower than 1.25kg in their weight plates and only 2.5kg increments for dumbbells, once above 10kg. If you can find a way of getting in between these increments, or if your gym just has smaller increments, good for you – you can train more accurately and will likely progress even faster.
Try to perform as many reps as you can at the weight you set for each exercise. The rep counts you score for each exercise are your rep targets.
If you score lower than 6 reps in any given compound exercise at a training intensity of 80% then you are likely more fast-twitch dominant in the related primary muscle group(s), and training these muscle group(s) with lower than 6 reps would be optimal (if you are an intermediate). Whereas if you score more than 10 reps in any exercise at a training intensity of 80% then you are likely more slow-twitch dominant in the related primary muscle group(s), and training these muscle groups with higher than 10 reps would be optimal (as an intermediate). In either case performing as many reps as you can in each exercise at your given optimal training intensity, based on your level of advancement, factors in fiber type composition and the rep count you score here is your likely optimal rep target.
Combined with the set-volume you determined in step three, these are your optimal training parameters.
You now train each exercise at it’s specific rep target, aiming to increase the weight gradually, while staying as close to that many reps as you can, with each muscle group’s specific weekly set-volume.
See the above as guidelines. In practice you want to use the combination of training intensity and set-volume that enables you to progress the fastest, and there is an element of intuition involved too. After determining your genetic potential and relative development in each muscle group pay attention to how you actually perform in the gym when applying these guidelines – You may need to tweak and fine tune a bit.
Remember that you will likely end up using different training intensities and set-volumes for different body parts, depending on each muscle group’s genetic potential, fiber type composition and level of advancement. This will be especially so if you have trained like a regular gym bro for the first two years of lifting and never missed a chest workout, but still haven’t found out where the seated calf raise machine is at your gym... Or if you’ve trained like the regular fitness chick and can squat more than most of the guys at your gym but have maybe skipped on your upper body a bit.. Or all together.
To help understand how it might work in practice below is an example in figuring out the optimal rep target and set-volume using the back squat, for an intermediate level trainee of average genetics and a body weight of 89kg.
Step One: determine one rep max
3RM after warming up = 120kg X 3 reps
Epley Formula to estimate 1RM = 120 X (3/30 +1)
Estimated 1RM = 132kg
At a body weight of 89kg, and average genetics, this puts him around the start of the intermediate category, for quads and probably glutes.
(A more accurate picture of genetic potential in his glutes could be painted when combined with his deadlift 1RM).
Step Two: determine optimal training intensity
As someone at the start of the intermediate category he should use a training intensity of 80% for compound exercises.
80% of 132 = 105.6kg
105.6 kg is likely to be the optimal weight for his current strength level, and the number of reps he can get at this weight is likely to be his optimal rep target.
Step Three: determine optimal set-volume
As an intermediate lifter he should use between 16 and 18 sets per body part per week to progress optimally.
As he is at the beginning of the intermediate category it might be wise to start with 16 sets per week and possibly later increase set-volume to 17 sets and later still, to 18 sets, once a rate of progress has been established for 16 sets, to be able to compare the different set-volumes’ rate of progress, for the sake of fine tuning. If progress is better than expected at 16 sets, however, then there would be no need to increase the set volume from 16, as it is probably already fairly accurate.
Note that this is not his set volume for the back squat only, it is his overall set volume for the quads. If he is doing other exercises that effectively train the quads, like leg extensions or other squat variants, then these would also be counted toward his overall 16 weekly set-volume for quads.
Step Four: determine rep target
In the next training session he would warm up, set the weight to 105kg and gets as many reps in the back squat as he could at this weight.
Say he gets 9 reps, this is then his likely optimal rep target.
He uses 9 reps as his rep target for back squats and aims for 16 sets per week for quads overall, including any other quad exercises in his program (which would each have their own optimal rep target to be calculated too).
In practice the optimal weekly set-volume per body part can vary from 10-30 sets in any individual, and increases with training age, however the above guidelines are a good start. Certain lifters with better-than-average genetics can sometimes tolerate a much greater set volume than the above recommendations, in each of their respective strength categories.
Elite level lifters in particular, also endowed with extraordinary genetics, can sometimes beneficially push this set-volume limit up all the way to 56 sets per body part per week. The set volume should be pushed up gradually though, for as long as progress is still occurring, and with carefully controlled recovery conditions, until progress begins to taper off – as the indication of overreaching. This is usually done with a high training frequency - each body part twice daily.
Training frequency (the number of times you train each muscle group per week) is another important variable related to optimal hypertrophy training, which also increases with training age. Read more about the optimal training frequency here.
If you want to have all these variables calculated for you and put together into a personalised training program, hire me as your online coach - if I have availability I would love to help you!
For the record, as a certified Bayesian Bodybuilding coach I have a calculator that I use which gives an estimate of how close any trainee is to their own genetic potential, in terms of circumference of body parts, at a given body fat. It tells me how much growth can still likely be achieved in each body part, and from this I get an estimate of how developed each body part is relative to its specific genetic potential. When combined with strength tests that I run on each body part with every client at the start of their training, it gives me a fairly accurate understanding of where each trainee’s body part is along its journey to full muscle development. I then apply this in my program design for each client to be better able to bring up lagging body parts and effectively max out already well developed body parts. If you are interested in getting hold of this tool and learning how to use it yourself and/or in learning more about how to optimise an individual’s training program, I recommend taking the Online Bayesian Bodybuilding PT Course. It is designed for trainers and strength coaches but any serious lifter would benefit to learn the science behind their own training too.