Natural limits of muscle growth [with calculator]

Recently, during one of my research sessions across the internet, I suddenly had one question coming to mind: are there only steroid-powered monsters on Youtube?

That ultimately led me to the following topic: how much muscle growth is naturally possible, anyways?

I have to admit that this is a very provocative topic. But once I have experienced myself how scarily low the inhibition threshold for using anabolics and other banned substances can be for many fitness freaks. Sure, many young people storm to the gym because they want to look like Chris Hemsworth as Thor or Arnold Schwarzenegger is his prime. The only results that count are the ones you can see. In addition with the wonderful feeling of invincibility that you still haven’t lost in your youthful days, many might think: what can go wrong? Why work for years if you can achieve the same result in mere months?

Sixpack with anabolics?

Reach your goal faster with a little shortcut

A study of the German Department of Health has supported these claims with numbers: especially men and women in younger ages (19-29 years) that regularly visit a gym tend to use prescription drugs and substances to increase their performance (cf. KOLIBRI survey (German source)).

Next to movie stars, the countless Youtube celebrities and Gangster Rappers celebrating bodybuilding certainly play a big part in the heightened desire for muscles in young athletes. So when these role models flaunt their muscles, their fans try to match them – whatever it takes. A few then take the seemingly easy shortcut by using anabolic steroids. It all intensifies even more when there are more ambitions and there is money to be earned.

Biceps Curl muscle growth

Social Media as fire accelerant

In our modern times with various forms of media all over such innovative channels as Youtube, Facebook or Instagram, it has become increasingly easy for everyone to turn their body into a brand. There are countless self-proclaimed muscle growth experts and fitness professionals that also look like Ken. And all natural, of course! Gotta keep it authentic. Have all these Youtube celebrities achieved their perfect bodies with total devotion and a disciplined lifestlye? It could also be that there are similar problems that the professional bodybuilding scene also has with certain bad apples that prefer to cheat…

Does Bodybuilding have a Steroid Problem?

This blog post is not about shedding light on the dark areas of bodybuilding and I certainly don’t want to tar every athlete in this aesthetic sport with the same brush. They are out there, the honest and natural bodybuilders!

Does one negative test prove innocence?

‘But there are tests during competitions!’ is what one or two of our readers might say. And yes, that’s certainly true! But even if and when most professional bodybuilders have had several negative tests throughout their career it doesn’t really prove total steroid abstinence, especially when it comes to juicing in the past. If you have used steroids regularly for a longer period you might profit from it even years after stopping. Just consider that Lance Armstrong never tested positive in his career as far as I can remember…

This is probably the reason why it seems so tempting for hobby Arnolds to administer ‘a little help during mass phase’. Abandon drugs afterwards and start the definition phase. It sounds so easy and yet so many get stuck.

Well, before I go on too much I will turn my attention to the real topic of discussion in this post. I wanted to address the natural limits that you, as an active sportsman, succumb to. In other words, how much muscle growth can you achieve with real food and honest and hard work in the gym? How many gains will mother nature grant you? What is your genetic potential?

How much muscle growth can I achieve?

How much muscle growth can I achieve?

There are several different studies and theories. The authors of these theories are former bodybuilders, sports medicine specialists, or strength and conditioning coaches. All have one thing in common: there is a natural limit! But this limit is different for everybody. There are several methods and models to determine where your individual limit lies. At this point we have to state that we certainly don’t claim to have the one and only solution for this elemental question or that we know which model is the best. All of these models are build upon experiences and studies and none of them claim to be as holy as one of the ten commandments.

The Alan Aragon Model

Alan Aragon is an American coach, author, and speaker for the National Academy of Sports Medicine and the National Strength & Conditioning Association, among others. According to his theory, a beginner can grow 1% – 1.5% of their bodyweight as new muscle mass per month. So a man of 100 kg can gain 12 – 18 kg of new muscle in the first year. In the second year (you are now an intermediate), 6 – 12 kg are possible. During the third year the rate slows down considerably. Then, only 3 – 6 kg of muscle mass are possible. So after three years of continuous training, a man who weighed 100 kg at the beginning could weigh 121 – 136 kg at the end of the third year. The following table will show you the rates graphically:

Training statemuscle growth/month
Beginner1 – 1.5% of bodyweight
Intermediate0.5 – 1% of bodyweight
Advanced0.25 – 0.5% of bodyweight

Casey Butt’s Frame Size Model

The natural bodybuilder Casey Butt has done a study with several colleagues and made the claim that genetic potential and physique correlate closely. He examined the girth of ankle and wrist, body height, and the current bodyfat percentage (BFP). The following formula was the result:

Height^1.5 x [(√wrist)/22.6670 + (√ankle)/17.0104] x [(BFP%/224) + 1] *

This calculation has a little disadvantage: you have to know your current bodyfat percentage. You can measure it using the Calipper method (measuring the skinfold thickness) or a valid bodyfat scale. If you want to know how much muscle mass would be possible to achieve in the following training year with a certain desirable BFP you can use the following deduction:

0.3 × wrist^2 × 0.5^(training years – 1) *

The result is the possible additional muscle mass at about 8 – 10 % BFP.

As you can see, Butt also takes the training experience (in time) into account. As your training experience grows the muscle growth decreases. I, for example, could add about 1.57 kg this year because I have been training regularly for a pretty long time now. Trust me, I’m working on it 😉

The Fat-free Mass Index

The Fat-free Mass Index denotes a value that is supposed to give insights to the general body composition and is more meaningful than the well-known BMI (Body Mass Index). The BMI is misleading because a well-trained man can easily have a BMI value that points towards overweight. Since this value only incorporates height and weight it shouldn’t be considered at all because it can’t differentiate between ‘good’ overweight (muscle mass) and ‘bad’ overweight (fat).

To calculate your Fat-free Mass Index use the following formula:

FFMI: fat-free mass / (height x height) + 6,3 x (1,8 – height)

The fat-free mass can be calculated like this:

FFM: (bodyweight x (100 – bodyfat percentage in %)) / 100

*: ankle and wrist in inches, the result is in pounds

∆: mass in kg, height in centimeters

What makes this formula so interesting is this: a team of scientists at the McLean Hospital in Massachusetts conducted a study of professional bodybuilders. They concluded that athletes that don’t take anabolic steroids have an Index of around 25 at max. Steroid users could surpass that value, often by much. This leads to the conjecture that the FFMI of around 25 is a natural limit. Or to put it differently: up to a value of 25 the body can regulate its building processes hormonally and energetically by itself. Provided the diet is right and the training impulses are optimal. Beyond that point, steroids have to come in.

The aerobis Fat-free Mass Index calculator

We have programmed you the ultimate aerobis Fat-free Mass Index calculator. Simply put in your values and find out your Fat-free Mass and your Fat-free Mass Index.

Your results

If you want to find out how much muscle mass you can build up theoretically, just increase the bodyweight value or reduce the bodyfat value until the FFMI settles around 25. Please consider that a bodyfat percentage of 6 % and below is unhealthy and can only be reached by professional bodybuilders for a few days (during competitions). Desirable would be a value of 10 – 12 % for men. Our calculator tells me that I still have about 18 kg of muscle mass to gain.


At the end of the day, there are many theories and models. Some are actually relatively useful and one has even been backed by a study. But you shouldn’t get hung up on these values because they describe the genetic potential of building muscle mass under optimal conditions and continuous training. And these training conditions can, as far as I am aware, only be met by professional bodybuilders that can dedicate a lot of time and invest a bunch of money on their training regimen because marketing deals and other business models alow them to worry about nothing else. To reach your natural limit it takes complete dedication and focus. This is not a hobby but a way of life! Never miss a workout, perfect diet, sufficient regeneration and sleep, push your body to its limits every time – not a lot of people can and will actually do that.

To bridge the gap to my introduction and the mentioned Youtube coaches and celebrities: you would have to take a closer look at their lifestyles. Do they have perfect conditions for their training and the complete focus? Or can they create these conditions for themselves? If you have a regular job I don’t think that it is possible. But if you are lucky and are one of the few that actually make good or even great money with your channel you will have the time to workout all day and film yourself doing it 😉

What do you think?

Are all the muscles that you see on Youtube, Facebook, and Instagram real? Or are these guys just pushing air?

And remember,
get functional!
Your Fabien

Author: Fabien Mpouma

Fabien is bachelor of arts sportscience (DSHS) and since his studies he is working in the sector of health- and rehabilitation sports. He was course instructor for several institutions in the field of rehabilitation and mental and physical disease. He has a lot of experience in prevention with adults, youths, and children. He worked as regional manager for Outdoor Gym and now as a Personal Trainer and Foodcoach. Since 2014 he is Manager for Training & Education and Head Coach for aerobis. In 2016 he opened his own facility for Personal- and Grouptraining in his hometown Siegburg. Stay in contact with Fabien by sending him an email

3 Comments Leave a comment

    Michael 12. July 2015 at 9:20 AM #

    Hi Fabien,
    erstmal Kompliment zu Deinem tollen Beitrag.
    Der einzige Bodybuilder dem ich abgekauft habe, dass er „natural“ Bodybuilder war ist Vince Gironda. Wenn ich mir Bilder von ihm ansehe und diese mit anderen auf YouTube vergleiche, fällt es mir schwer die heutigen Bodybuilder ernst zu nehmen. Zwar gehört auch neben dem Doping viel Disziplin und Wille dazu, aber die langfristige Gesundheit für diese kurzfristigen Erfolge aufs Spiel zu setzen werde ich nie verstehen.
    Gruß Micha

  2. Fabien Mpouma 14. July 2015 at 9:29 AM #

    Das werde ich auch nie verstehen. Aber ich habe, genauso wie Du, größten Respekt vor der Hingabe und Disziplin dieser Athleten. Ich bin auch ein großer Fan von Vince Gironda. Allerdings von seiner Trainingsphilosophie und seiner Art des Programmings. Ich kann Dir nicht sagen, ob er clean war oder nicht. Allerdings weiß man ja, dass einige seiner Athleten schon nachgeholfen haben. Meinst Du, dass der Trainer bei diesem Punkt eine Rolle spielt?
    Viele Grüße aus Köln

    Ben Menges 15. July 2015 at 2:58 PM #

    Hey Fabien!
    Respekt für die Leistung habe ich auch. Ob mit oder ohne Stoff haben viele Leute hart gerarbeitet. Wenn sie das Risiko eingehen wollen von mir aus. Was ich schlimm finde ist dass Anfänger, die teilweise noch nicht mal trainieren sich Sachen spritzen und dann ein bis maximal zwei mal ins Studio gehen – meistens in welches ohne Trainer und Einweisung. Unglaublich eigentlich wie viele junge Menschen da mit ihrem Leben spielen.
    Mindestens genauso erschreckend ist die Tatsache, dass ich nur noch sechs Kilo Muskelmasse aufbauen könnte! ;D Sehr interessanter Rechner ist das. Wenn ich mit meinen Werte spiele komme ich auf Ergebnisse, die ich aus Trainererfahrung auch so absegnen kann. Also dann mal ran ans Werk!

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