A topic that has been argued for ages and comes along with many questions, to mention some:

Do muscles stop naturally growing at a point?
Do all professional bodybuilders take steroids to grow that big?
How big can I be without steroids?
What if I trained so hard, and eat so right, will I keep growing?

The problem is that from mainstream viewpoint, it’s still promoted that even biggest muscular guys can be steroids free, whether by the media or naive people.
That can’t be further from the truth, unless you are a mutant genetic freak, you will never achieve the muscle mass that pro hold without using drugs.

Think about it this way, when you see a huge impressive bodybuilder somewhere, the first thing that pops in your mind " ahh that’s just not natural), well my friend, your mind is probably right, he is not natural, he wouldn’t be dropping jaws if he was.
Human body has limits; you heard that your response to training, nutrition, supplement and other will depends on your body nature.
Which is totally true, but what is the body nature?
Body nature depends on lots of genetic factors that affect our body response beyond just moving weight and eating food, its things like body type (Ectomorph, endomorph and mezomorph), bone structure, mental factors, hormonal capacity, recovery capacity, individual anatomy, insulin sensitivity, myostatin availability and more. The largest muscle size you can ever achieve is determined in combination of this entire individual genetic predisposition; it also depends on your workout pattern, consistency, effort, and nutrition.

Eventually you will hit a plateau and stop growing, to grow beyond that you can push your limit by using anabolic steroids, Growth Hormone, IGF-1, Insulin and others, even after that you will hit a plateau, and keep looking for more drugs, or higher dosages, which will make you hit a number of plateaus and breaking them, and eventually get stuck in one.

Why does the body stop the muscles growth ?

Muscle is expensive to make and expensive to sustain, the body will only make muscles if there is a good reason to do so, that’s why it’s not easy to get muscles, and it requires very hard exercise to stimulate the growth of bigger muscles, however it’s not that a continues application of this stimulus will result in a never ending growth, at one point the body will stop making new muscles.

Muscles requires around 100 calories a day to keep an extra kilogram of muscle alive. The body needs the calories to do many other important functions in the body, so the body weighs its needs for additional muscle energy supply against its other needs.
Extra muscles need requires more thermoregulation by the body, for it to be in a stable temperature (37.C) and function properly.
Our body produce heat in proportion of our mass, and dissipate it in proportion of our surface area, if you increase your muscles, you actually increasing the volume (body mass) 3 times greater than you increase the surface, therefore the body cooling efficiency drops.
Ever wondered why pro bodybuilders sweat their ass off without doing much effort, the body just struggles to maintain its temperature.

Myostatin and Muscle growth

Myostatin is a protein in humans and animals that regulates muscle growth. Myostatin sends a signal that determines how large a muscle can become. When a muscle approaches the limits of its size, myostatin stops any further size increases.
Myostatin is one of the most important factors that determine how much muscles you can gain, it’s all based on your genetics, the higher the level of myostatin a person have the less muscle they will build, the only way to know how much myostatin that you have is by undergoing the quest for maximum muscles growth yourself.

However many scientist believe that eventually there would be some way to control the myostatin gene, allowing more muscles growth and a cure for muscular dystrophy and other diseases, of course i can only imagine the monsters that would be on bodybuilding stages if that happens.

Check out theses studies and findings about myostatin:

The gene encoding myostatin mighty mice experiment that was discovered in 1997 by geneticists Alexandra McPherron and Se-Jin Lee producing a strain of mutant mice that lack the gene. These myostatin "knockout" mice have approximately twice as much muscle as normal mice. These mice were subsequently named "mighty mice".

Dr. Markus Schuelke, reported a case in the New England Journal of Medicine of the first known human where a mutant DNA segment was found to block production of a protein called myostatin that limits muscle growth. The boy has a genetic mutation that boosts muscle growth. He has twice the muscle and half the fat of other children his age.

A whippet named Wendy has a bizarre condition that has slowed her myostatin production. Resulting in a great increase in the muscle mass as you can see in the picture.

A strain of cattle known as Belgian Blue are predisposed to genetic conditions, a natural mutation of the gene that codes for myostatin, the protein that counteracts muscle growth, myostatin is unable to function in its capacity, resulting in accelerated lean muscle growth, due primarily to hyperplasia rather than hypertrophy.

Now we realize that our muscles has a limit, and it depends on many factors that are hard to control, but we can just do our best in the one we can control, training, eating, and resting in the best way to promote growth.

Let’s take a look at a study that compared athletes who use anabolic-androgenic steroids with athletes who don’t:

Biological Psychiatry Laboratory, McLean Hospital, Belmont, Massachusetts 02178, USA.
Abstract:
We calculated fat-free mass index (FFMI) in a sample of 157 male athletes, comprising 83 users of anabolic-androgenic steroids and 74 nonusers. FFMI is defined by the formula (fat-free body mass in kg) x (height in meters)2. We then added a slight correction of 6.3 x (1.80m - height) to normalize these values to the height of a 1.8-m man.
The normalized FFMI values of athletes who had not used steroids extended up to a well-defined limit of 25.0. Similarly, a sample of 20 Mr. America winners from the pre steroid era (1939-1959), for whom we estimated the normalized FFMI, had a mean FFMI of 25.4. By contrast, the FFMI of many of the steroid users in our sample easily exceeded 25.0, and that of some even exceeded 30. Thus, although these findings must be regarded as preliminary, it appears that FFMI may represent a useful initial measure to screen for possible steroid abuse, especially in athletic, medical, or forensic situations in which individuals may attempt to deny such behavior.
PMID: 7496846 [PubMed - indexed for MEDLINE]

This study showed that natural athletes FFMI didn’t extend to the limit 25, based on the samples and 20 Mr. Universe winners (era before steroids use was common), however the steroids users sample easily exceeded 25, and some even exceeded 30.

To know your Fat free mass index, you have to know your fat percentage, convert it to kg, and then subtract it from you total weight to get fat free mass, then apply this equation:
(FFM/height2)

Example:
a 170cm person weighing 80kg with 10% bodyfat, will have a FFMI of the following:
80 x 10% = 8kg fat in kg
80 - 8 = 72 fat-free body mass FFM
72 / 1.7 X 1.7 = 24.9

The FFMI is 24.9, which mean this person is almost at his limit of muscle gain, and won’t probably be gaining any more muscle in natural way, I know it can be very disappointing, but numbers can’t lie, this is based on research, of course every rule has an exception, but it’s very rare.

Casey Butt has a very useful site I found that gives you an approximate of what your maximum bodyweight and maximum drug free body weight measurement based on sound methodology that line up with the FFMI results.

Click here to know your
Maximum Muscular Bodyweight and Measurements Calculator
Maximum Drug-Free Bodybuilding Potential Calculator

Summary:
The human system (any biological system for that matter) can only adapt to a finite and specific amount of stress until it eventually stops or even break down. How many of you natural bodybuilder hit a limit and just couldn’t pass above it no matter what you do, increasing the calories ending up gaining fat rather than muscles, the body just adjusted as far as it can to the new stress, if you overstress it, you may fall behind by over training, don’t think you are superman and you can do it naturally, sadly, there is no way you will look anywhere near pro bodybuilder naturally, however you still have the chance to look the best you can do.

This is not to disappoint you, when I first started training bodybuilding I believed that pro bodybuilder can be natural, and just train and eat very good, getting more into the sport, your eyes just opens, and naivety clouds are gone, there is no way that naturally you can look unnatural.
For natural bodybuilders, I really pay all the respect, as it takes more work to achieve small results, whether its principles, ethics or want to remain healthy reason, it’s a personal option to stay natural, and all the respect goes to you.

Last thing I want to say, if you reached this point of the article and think you reached your limit, so why would I go and train, or continue bodybuilding, I would just say, if you are one of those people, then you probably didn’t even get close to your limit, a quitter won’t reach their potential in anything.
For people who say this is none sense and they can still reach high levels, higher and higher, I salute your determination and strong will, and wish you all the best in your goals.

Shady Eid is a certified Personal Trainer, writer and competitive bodybuilder based in UAE, for questions and comments you can contact him at: Shady@arabianmuscles.com