RE: Predicting Your Muscular Potential

Categories: Miscellaneous

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.

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About the author

Menno Henselmans

Formerly a business consultant, I've traded my company car to follow my passion in strength training. I'm now an online physique coach, scientist and international public speaker with the mission to help serious trainees master their physique.

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