There’s an old myth that natural lifters can get up to a fat-free mass index (FFMI) of 25. The idea is that if someone has an FFMI under 25, they stand a good chance of being natural, whereas if their FFMI is greater than 25, they’re probably lying about being natural.
FFMI is your lean body mass. It’s your body mass index (BMI) with the fat taken off. It’s a popular way for bodybuilders to compare their size, since it measures how much muscle they have while (somewhat) accounting for height.
That old myth is wrong in two ways:
Natural lifters with outlier genetics often exceed an FFMI of 25. There are many examples of this. I’ll go over three of my favourites.
Most natural lifters probably can’t get to an FFMI of 25. It’s bigger than you think, especially if you have a smaller frame.
Unfortunately, that makes it really hard to tell if someone is natural by looking at their FFMI. It also means that aiming for a natural FFMI of 25 isn’t a very good approach. It works better if you try to account for your genetics. You can do that by factoring in the size of your bones. I’ll go through all of it, then give you a calculator you can use.
We’re going to be talking about FFMI, so it might help to calculate your own. That will give you a good frame of reference.
FFMI Calculator
Fat-Free Mass Index
The Myth of the 25 FFMI Natty Limit
The myth of the natty limit comes from an old Kouri study from 1995 (study). Kouri and colleagues recruited 157 men from local gyms around Boston and Los Angeles. 83 of them were using steroids. 74 were natural. None of those natural lifters had FFMIs of over 25, but about half of the steroid users did. This suggests that most natural lifters don’t have an FFMI of over 25, but it says relatively little about what’s physically possible, especially when looking at outliers.
In that same Kouri study, the researchers estimated the FFMIs of champion bodybuilders from the pre-steroid era. Most of those natural bodybuilders had FFMIs of over 25, with three of them having FFMIs of over 27. Let’s go through some examples.
Natural FFMI Examples
Jeff Nippard
In Jeff Nippard’s latest transformation video, he had his body composition professionally analyzed, giving him a weight of 75 kilos with a body fat percentage of 14% at a height of 5’5. That puts Jeff Nippard’s FFMI at just under 24:
An FFMI of 24 might not sound impressive, but it absolutely is. Most natural lifters never get close to this. Even if they did everything right, it might not even be within their genetic potential. But before we start talking about what’s realistic for you, let’s look at some more extreme examples.
Steve Reeves
Steve Reeves is the most famous natural bodybuilder from the pre-steroid era. At his peak, he claimed 220 pounds at a height of 6’1. If we estimate his body fat percentage at around 12%, that gives him a natural FFMI of just under 26.
Some people argue that Reeves might not have been natural. Steroids were invented in the 1930s and used to treat hypogonadism. In the 1950s or 60s, some athletes discovered that they could improve performance, recovery, and muscle growth. By then, though, Steve Reeves was already incredibly muscular, and he didn’t suddenly pack on a bunch of extra muscle. I think he’s an example of someone with a strong frame, a big and nutritious diet, and decades of vigorous training.
Let’s assume the worst. Let’s say Steve Reeves wasn’t natural. Maybe people started juicing earlier than we think. In that case, let’s go back a few decades to look at someone even bigger.
Herman Goerner
Consider Hermann “The Mighty” Görner, a strongman from the 1920s, decades before steroids were invented. He was famous for feats of strength like deadlifting 725 pounds with one hand. At his peak muscularity, he was 6’1 and 245 pounds with abs. That’s a natural FFMI of 29.
He doesn’t have the huge quads of a modern bodybuilder, but you can see how robust his bone structure is, how strong his core muscles are, and how thick his neck is. He’s built like a bull.
George Hackenschmidt
If we go back another 20 years, to 1900, we get George Hackenschmidt, the famous strongman and wrestler. He was famous for pressing 335 pounds overhead. Even more impressively, he could press 275 overhead with just one hand.
It’s hard to know his exact stats, but the numbers I see are 220 pounds at a height of 5’9, and perhaps a body fat percentage of 18–20%. That puts his FFMI at close to 27, with no doubt whatsoever that he’s natural.
How Genetics Influence Muscularity and FFMI
The first thing to realize about FFMI is the relationship between bone mass and muscle mass. If we imagine two guys of the same height, one with a skeleton that’s thick and broad, the other with a skeleton that’s thin and narrow, then the thicker skeleton might weigh about 10 pounds more, bumping his FFMI up by about 1 point.
However, the bigger your bones are, the more muscle mass they can support. Also, the same androgenic hormones that cause us to develop thicker bone structures also tend to cause us to be naturally more muscular. So, the guy with the thicker bone structure might have a skeleton that bumps his FFMI up by 1 point, but then those bones allow him to gain an extra 30 pounds of muscle, bumping his FFMI by another 3 points. That can be the difference between a natural FFMI of 22 and 26.
There’s a little more to it than that. Different people start with different amounts of muscle mass and have different responses to the stimulus of lifting weights. For example, when I was 21, I was 120 pounds at 6’2 with a body fat percentage of around 12%, putting my FFMI at 13.5. That’s extremely low. Part of that is because my bone structure is so thin, but I also had extremely little muscle mass.
In the above photo, I’m at 130 pounds (FFMI 15) on the left and 205 pounds on the right (FFMI 23). My bones are very thin, so I’m guessing they weigh a few pounds less than normal. What made the bigger difference, though, is gaining 75–85 pounds of body weight. I’m confident I could keep going. I wouldn’t be surprised if I could gain another 20 pounds of lean mass. But I don’t think it would be possible for me to bulk up to an FFMI of over 25, and I’m not sure I’d want to weigh that much anyway.
How Can You Tell If Someone is Natural?
There’s this idea floating around that if someone’s FFMI is over 25, then we can’t say for sure that they aren’t natural, but we should at least be suspicious. But that isn’t how it works. You’d expect the guys with the best genetics to become the bodybuilders, influencers, and fitness models. We aren’t looking at a random sampling of people. Their FFMI doesn’t tell us very much at all.
So, there are other heuristics people lean on:
How quickly did they gain muscle?
Did they have a sudden spurt of muscle growth?
Are they building muscle very leanly?
Do they have acne or gyno?
Are their shoulders disproportionately developed?
Are they surprisingly weak for their size?
Are they developing bigger facial muscles?
Is their skin turning red?
Is their voice changing?
These are all just guesses, though. We can’t really know. And I’m not sure it matters very much anyway. Whether an influencer is natural or not doesn’t tell us anything about whether their results are realistic or not. If they have top 0.1% genetics and we have bottom 20% genetics, our results won’t look the same as theirs anyway. Whatever’s going on with them, we still need to figure out a way to determine our own natural muscular potential.
Realistic FFMI Goals for Natural Lifters
Dr. Eric Trexler, from the MASS research review, went through the research, trying to figure out what FFMIs were realistic for natural lifters:
Bad Genetics: A man with bad muscle-building genetics can expect to bulk up to an FFMI of about 21. That’s a little bit more muscular than Brad Pitt in Fight Club. Maybe as big as Brad Pitt in Troy. That’s enough to be perfectly healthy. It’s also enough to look athletic and attractive.
Average to Good Genetics: A man with average genetics can get up to an FFMI of about 22–23. That’s enough to look impressively muscular, especially if you’re lean. You’re comfortably beyond the level of muscularity most guys want to have. You’re more muscular than the bodies women dream about.
Great Genetics: Guys with great genetics can get up to FFMIs approaching 24 or even 25, especially if they’re willing to gain some body fat to do it. These guys are winning natural bodybuilding shows. They look like very impressive bodybuilders. Jeff Nippard is 5’5, 165 pounds, and 14% body fat, giving him an FFMI of 24.
Elite Genetics: Guys with elite genetics can get up to FFMIs of well over 25, and sometimes much higher (study). Human variation is extreme, especially when we’re looking at the long tails of normal distribution. Guys with one-in-a-million genetics can get absolutely enormous. These are the most famous natural bodybuilders in the world, the record-breaking strongmen, professional sumo wrestlers, and NFL linemen.
This gets a little tricky because by far the biggest muscles in the human body are the quads and glutes, and most guys aren’t that interested in building enormous quads and glutes. That takes a point or two off their FFMI without really affecting their appearance very much. That means if you’re built more like a fighter or a gymnast, with a bigger upper body and a smaller lower body, you can look muscular at a lower body weight, with a lower FFMI.
Muscular Potential Calculator
That brings us to the end. It’s time to calculate your natural muscular potential. You can do that here. It’s a simple calculator, like the FFMI calculator above. It’s just that I can’t have two calculators on the same page. It’s for the best anyway. I go into all the details and nuances in the article beneath the calculator.
Shane Duquette is the co-founder of Outlift, Bony to Beastly, and Bony to Bombshell. He's a certified conditioning coach with a degree in design from York University in Toronto, Canada. He's personally gained 70 pounds and has over a decade of experience helping over 10,000 skinny people bulk up.
