RE: Predicting Your Muscular Potential

From the ancient Greek artists to modern day bodybuilders, from aesthetic ideals of human proportions to haters and from controlled, statistical predictions to baseless claims, many individuals have developed formulas to predict people’s maximum muscular potential. However, despite such wide interest, the allure of genetic certainty and the fear of uncontrollable limitations have caused more controversy than they solved.

After reading this article, there should be no more controversy. Actually, it won’t be this article, because someone else already found out there is much research on correlates of muscular potential. This person was Casey Butt and he is, to my knowledge, the only person that has presented a sensible and reasonably accurate formula to calculate your own maximum muscular potential.

You may protest there is no such thing and everyone can achieve whatever they want as long as they believe in it and are motivated enough. Yeah, tell that to the short kid who wants to be the next Michael Jordan of basketball.

As Howard Gardner put it,

I align myself with almost all researchers in assuming that anything we do is a composite of whatever genetic limitations were given to us by our parents and whatever kinds of environmental opportunities are available.

We are not all equal. In fact, the most valid argument against most of these formulas is that there is too much genetic variation in the population to make accurate predictions at the individual level. As any statistician would tell you, if you have a really simple model that leaves a lot of variance unexplained, you probably need to add predictors. Most of these formulas are based on a single predictor, most often height or wrist size. A simply formula like that will indeed only give you rough averages of averages which have no use at the individual level, but Casey’s formula is more complex.

If you’re interested in the nature-nurture debate and want to know how much genetics matter relevant to things you have control over, I recommend reading Bret Contreras’s The Truth About Bodybuilding Genetics. However, such knowledge doesn’t really have any practical applications. Maybe someday in the future we’ll have access to cheap DNA-tests that will tell you exactly how big your biceps can get, but for now we’ll have to do with estimations.

Do those estimations have practical applications then? Yes, there are at least 4 reasons why this information has relevance.

  1. It gives you a realistic long term goal, something to strive to achieve before age prevents you from doing so. Personally, I think such long term goals are crap, but I know they motivate many people.
  2. It allows you to realistically compare yourself with others. Ideally, you should only compare yourself with your previous self, but it’s human nature to make interpersonal comparisons anyway, so you may as well be good at it.
  3. It allows you to know who to take advice from. I think it was Dorian Yates that said you should take advice on a topic from those who are naturally bad at it. People are inclined to do the opposite. They copy the chest and biceps routines of Schwarzenegger and the leg routine of Tom Platz. Don’t. Take advice from the hardgainers and people built like yourself, people that had to overcome their limitations instead of following their talent.
  4. It allows you to identify weak body parts and measure your structural balance.

So, without further ado, here is a link to Casey Butt’s Your Maximum Muscular Bodyweight and Measurements and here’s a direct link to an online calculator where you just have to plug in your measurements. To give you a primer, Casey’s formula takes into account frame size, height and body fat percentage. Those are arguably the most important and especially the most practical predictors, but there are many more signs.

Take a look at the list of of positive predictors of your maximum muscular potential below. The higher you score on any of these variables, the higher your potential.

  • Your birth weight. There’s a reason the Spartans threw away frail babies.
  • The amount of lean body mass you carried before you started training. The most gifted individuals were already large before they ever touched a weight.
  • The fullness of your muscle bellies. Longer muscles of course have more mass potential than shorter ones. As a proxy, flex one of your elbows to 90° and see how many fingers you can put in between your elbow and your biceps. 0 is amazing, 4 is terrible.
  • Development of secondary sex characteristics, like a square face and lots of body hair. This is indicative of high testosterone.
  • Your second to fourth digit length ratio. The shorter your index finger and the longer your ring finger, the higher your prenatal exposure to testosterone.

These are not just fun facts. They’re real indices of your maximum muscular potential. Think about how most professional strength sport athletes look. They tend to have large, masculine builds.


The short version of this article: if you would not look out of place in this group, you have great potential in strength sports.

If you scored badly on these indices and now feel depressed… man up.

I don’t have a lot of respect for talent. Talent is genetic. It’s what you do with it that counts.

The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.



Associations between birth weight and later body composition: evidence from the 4-component model.Chomtho S, Wells JC, Williams JE, Lucas A, Fewtrell MS. Am J Clin Nutr. 2008 Oct;88(4):1040-8.

Effect of body build on weight-training-induced adaptations in body composition and muscular strength.Van Etten LM, Verstappen FT, Westerterp KR. Med Sci Sports Exerc. 1994 Apr;26(4):515-21.

Second to fourth digit ratio and the sporting success of sumo wrestlers. Tamiya R, Lee SY, Ohtake, F. Elsevier, in press.

See Casey’s article for his references.


  1. Haha says:

    Haha…what a bunch of bullshit…those guys look like they´ve been at it for a while….looks like olymic lifters or bad steroid users…

    • Menno Henselmans says:

      You missed the point. It’s not their muscle mass. It’s their secondary sex characteristic development.

  2. alex says:

    What you say may be right, but does it matter? I think very few people come even close to their genetic potential, so don't think too quickly that you're on a plateau because you reached your genetic limits. In my opinion and experience, even the guy with the worst genetics (except for handicaps or deformations) can theoretically reach a national level bodybuilding development. I think that, because of our terrible lifestyle, the average European individual is not even at 25% of his genetic potential in terms of muscular development. Somebody with bad genetics surely can, by using and intelligent and patient approach, develop a better body than someone with good genetics but much less knowledge and commitment. Nutrition and  the way you react on anabolics also play an important part in this. I think those kind of genetics are very important in performance athletes, but for bodybuilders (who seek purely hypertrophy) it is more complex. In my experience, a lot of top bodybuilders weren't worldclass performance athletes, and some of them even looked like ectomorphs when they started training. But once they touched a weight, they started growing like a weed. If, on top of that, they were gifted with awesome adrogene receptors, the puny boy can transform into a muscle morph. I've often witnessed that, while strong born farmer boys who started training thinking they would break down the gym soon, were struggling to make any progress. And last but not least: I don't think there is a correlation between the lenght of your muscle bellies, your prenatal exposure to testosterone and the thinkness of your fascia. The latter is much underestimated as a crucial factor in hypertrophy potential. My conclusion: genetics in bodybuilding are complex. A lot more factors are playing besides prenatal testosterone exposure, lenght of muscle bellies and bone thickness.
    Keep on the good work, Menno!

    • Menno Henselmans says:

      “In my opinion and experience, even the guy with the worst genetics (except for handicaps or deformations) can theoretically reach a national level bodybuilding development. ”

      I’m afraid to say I think you vastly underestimate the extent of drug use in professional sports.

      • alex says:

        No I don't. I never said that this guy "with the worst genetics" can reach this level without chemical assistance. My point is: even if you have bad genetics, with a proper amount of individualized training, fine tuned nutricion AND chemical enhancement (I prefer this term over "drug use", which sounds very negative), you can reach a decent level in bodybuilding. Most genetically gifted guys don't use their entire potential. Yates maybe came close, but guys like Dillet stayed far away from their optimal condition and still were huge. Arnold didn't have a clue of how to properly train, but still he excelled (and fooled millions of BB adepts into training his way). I'm convinced that, as knowledge grows, in the future we will see BB'ers who will dwarfen today's "stars". What the impact will be on the general health of those individuals, that of course is another discussion.

  3. alex says:

    By the way, I'm still curious for your insights on fascial stretching (using an extreme pump for hypertrophy). Arnold in his time already worshipped the pump, and now it has a revival with Haney Rambod a.o. , including some scientific back-up.

    • Menno Henselmans says:

      I haven’t read any convincing evidence that A) fascial stretching is possible or that B) it leads to hypertrophy, so I don’t think it is, but I have to say I’m not quite up to date on the whole fascia research.

  4. alex says:

    I'm busy reading all research articles on it, and I really think it makes sense. It's also the one and only reason why I recommend clients to stretch muscles post workout. I'm sure you will get updated and will share us your thoughts when the moment is right. Good luck with your site and all of your professional work. Nice to see a Dutch bodybuilding guru rising ;-)

  5. ProudDaddy says:

    I'm impressed by your articles or I wouldn't be making this request. I strongly suspect that a lot of the info in articles such as this would need to be modified for the elderly. I'm 71, been lifting 2years, and would have to gain 30 pounds of LBM to reach the formula potential. Not going to happen. I have also seen several studies that indicate our response to protein ingestion is less robust.
    Would you do an article or two on beating sarcopenia or somesuch? Thanks.

    • Menno Henselmans says:

      Thanks and props for staying fit at the age of 71! To be honest though, I wouldn’t count on such an article coming anytime soon. For the most part, things stay the same as you get older. They just get harder and you have to take into account that your recovery capacitites are not that of a 20 year old. There are some studies showing that optimal training design does indeed change in some aspects, but considering the demand for that kind of knowledge I’m going to have to be honest with you and not promise you an in-depth article in the foreseeable future. As a piece of advice though, do not let anyone tell you you shouldn’t do things because you can’t do them anymore at your age. Your body will tell you what it can no longer do. Pick joint friendly exercises, but use and try to improve the ROM you have and go as heavy as you still can.

  6. I am curious to find out what blog platform you
    happen to be working with? I’m experiencing some minor security
    problems with my latest site and I’d like to find something more safeguarded.

    Do you have any suggestions?

  7. Okay one criticism to this bit here:
    “As Howard Gardner put it,

    ‘I align myself with
    almost all researchers in assuming that anything we do is a composite of
    whatever genetic limitations were given to us by our parents and
    whatever kinds of environmental opportunities are available.'”

    As a friend of mine once said, it’s not what happens in life, but how you react to it. Individual effort does matter. Maybe to varying degrees, but it does. As you’ve said yourself, genetics are a given, so don’t worry about them.
    Worry about what you can control, rather than what you can’t.

    As for the last bit of the article, a bit emasculating, but yeah, which is more impressive–one who gets to his maximum muscular potential by sailing/coasting on his talent, or one who gets there by overcoming their difficulties and obstacles? That’s another way to put it. :)

  8. Anyone who knows anything says:

    You are determining genetics on a bodybuilding website and saying having a peak(shprt bicep) is a bad thing. Youre an idiot to say the least. I am a masters student and could come up with scientific studies to either disprove this or atleast explain the difference between total muscle and being a bodybuilder. Fuck head

    • Find me a scientific study showing how a shorter muscle can benefit total muscle mass and I’ll give you a month of free coaching. You may like the aesthetics of a biceps peak, but there is no question that longer muscle bellies favor total muscle mass.

    • Anyone who really knows anything says:

      Oh jesus! Watch out! We gotta masters student on the comment board. Let’s see that study…..fuck head.

    • joe santus says:

      Nowhere does the article’s author state that having a peaked biceps is a “bad thing”

      What the author does state is that, the shorter a muscle belly, then the less maximum size potential for that muscle. If two men are identical in all genetic traits except the length of the arm bicep muscle belly, and their training, nutrition, and other controllables are equal, then the man with the longer muscle belly will have larger biceps. The shorter the muscle belly, the fewer muscle fibers that exist to be enlarged.

      Balloons can illustrate the situation. Take two balloons, one four inches long and the other seven inches long. Inflate them both to four inches in circumference. Now, place them on a human skeleton where the arm bicep is located, with one end of each balloon up at the shoulder. Which arm looks bigger-muscled — the one with the shorter balloon or the one with the longer balloon? Note the gaps between the other, lower, ends of the balloons and the elbow joint? That gap is spanned by tendon, which attaches the lower end of the bicep to the elbow. Tendon doesn’t significantly enlarge, so that gap remains despite any training or weight-gaining that person might do. The longer balloons reduce that gap. Those balloons approximate muscle bellies. If those balloons are further expanded to, say, six inches of circumference as they sit there, which is going to look bigger? And — if that skeleton arm is flexed to a double-bicep pose, which balloon is going to look bigger as it’s compacted into the same relative space?

      The corollary is, a person with extremely short muscle bellies cannot build as large of muscles as person of the same skeletal frame with average length muscle bellies, nor can either of them build as much muscle size as a person with the same skeletal frame who has longer-than-average muscle belly lengths.

      Sergio Oliva and Larry Scott are examples of how excessively long muscle bellies can contribute to an arm having almost no peak; and, depending on preference, some dislike that “no peak” appearnace. But, fact is, their lack of peak is due to them being able to build even more mass in their arms because of extremely-long muscle bellies.
      Most world-class physique competitors don’t have quite that excessive of bicep muscle belly lengths, so do have a peak — but, they definitely do have longer-than-average muscle-belly lengths. That’s why they have the mass-potential for being world-class.

      And, none of this is anything novel or recently-realized. The primacy of muscle-belly length for mass had been known among bodybuilders long before I became a bodybuilder forty-four years ago in 1972 when I was age sixteen. Heck, even Art Jones, inventor of Nautilus, discussed it matter-of-factly in one of his writings in the late 1970s:

      Jones compares Sergio Oliva, who had little peak, and Casey Viator, who had a pronounced biceps peak — and makes the point that, though Oliva’s were even longer than Viator’s both men’s great arm mass was due to far-longer-than-average muscle bellies.

  9. BK says:

    Even more factors than listed here, for example the ACTN3 gene comes to the top of my mind. I know from genetic testing that I’m RX (intermediate deficiency in fast-twitch), my wife is XX (full deficiency in fast-twitch), children have a 50/50 chance of being either/or. I wonder, in addition to its impact on muscular potential, how it impacts fiber specific training as you advocate elsewhere.

  10. Lasso says:

    Menno, would you recommend DNAfit in order to find out more about our potential?

  11. Richardson says:

    proper training and nutrition have changed a lot of physiques even more than drug enhancement. I’m a trainer and I have seen it happen many times. steroids without proper workout regimens rest and food is like trying to drive a car without fuel no matter how powerful or big the engines are

  12. Zam says:

    Although I liked your article and your list of predictors is right I don’t think using a picture of a bunch of steroid freaks to illustrate your point about muscular potential is the best way to do it.

    “I align myself with almost all researchers in assuming that anything we do is a composite of whatever genetic limitations were given to us by our parents and whatever kinds of environmental opportunities are available.”

    I can see how drug users would willfully misinterpret this quote to have an excuse for their drug use. “Oh, I’m not cheating by taking drugs, I’m just taking advantage of the environmental opportunities available”.

    • As it happens I’m pro-drugs. I believe everyone should have the freedom to decide for themselves whether they want to use a substance that doesn’t harm anyone but themselves.

    • joe santus says:

      I’m age sixty; I began bodybuilding in 1972 at age sixteen. I’m still bodybuilding forty-four years later — still doing mainly free-weight compounds including barbell squats, overhead presses, pull-ups, dips, SDLs, deadlifts, rows, shrugs, etcetera. I ceilinged out on my natural muscle mass about the fifth year of my training, and have done the equally-intensive grind of maintenance lifestyle bodybuilding ever since, with focus on holding a 10%-12% BF six-pack for seven months of every year.

      I’m a lifelong-PED-free: no anabolic steroids, no prohormones, no growth hormones, no cutting drugs, not currently nor ever since I began bodybuilding at age sixteen.

      I’m also an under-averaged for maximum muscle mass potential — at 5’8″, I have relatively tiny leg bones (my ankles are 7.75″), small arm bones (wrists are 6.625″), narrow clavicles, wide-ish pelvis, and, very short muscle belly lengths everywhere (I can easily fit three fingers and almost a fourth finger in the tendon gap between my bicep and elbow). I haven’t declined steroids et al because I was satisfied with what genetics naturally bestowed on me. Yet, although I envy the physiques I expect were built with the aid of PEDs, I do not consider drug users “cheaters”.

      I do have an issue (same as most everyone does) with the dishonesty surrounding PED usage, especially in the marketeering sphere. But I definitely don’t consider careful, controlled PED usage by adults to be cheating. Although never a steroid user myself (and, during the late 70s, I could easily have obtained them from doctors by prescription if I’d wanted), I object to the current anti-steroid laws imposed on adults here in the USA. An adult (especially an adult outside of the “role-model” controversy inherent to adults in professional sports) ought to be free to choose whether or not to use PEDs.

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