Illustration of a skinny hardgainer with an ectomorph body type.

How to Know If You’re an Ectomorph

Most of us ectomorphs describe ourselves as being naturally skinny and we tend to have a hard time gaining weight. More specifically, though, ectomorphs are usually defined by having narrower shoulders, lankier longer limbs, thinner bones, and a lower body-fat percentage. Being an ectomorph is also associated with having a higher metabolism and a smaller stomach.

If you’re curious about whether you’re an ectomorph or not, there are a few simple tests that you can do. All you need to do is measure the width of your frame, the thickness of your wrists, and the length of your muscle bellies. You can do it at home in just a couple of minutes.

We’ll also cover how the various ectomorph traits affect our ability to build muscle, what our genetic muscular potential is, and how we should approach bulking up.

Before and after illustration of a skinny hardgainer ectomorph becoming muscular.

Do Our Bone Structures Affect Our Attractiveness?

In our article on aesthetics and attractivenesses, we dive deep into the most attractive male proportions. When it comes to your shoulders, the broader your shoulders are compared to your waist, the more attractive your body looks to women. Having naturally longer collarbones can help with that, certainly, but attractiveness is based almost entirely on how lean your waist is and how muscular your upper body is (study).

After all, having broad shoulders is just a proxy for strength, and having a lean waist is just a proxy for having a low body-fat percentage. If you have a muscular upper body and a lean waist, then your bone structure won’t matter very much. Women don’t care much about our body type, but they do care about whether we’re in good shape or not.

However, the more we understand our body type, the easier it’s going to be to get into great shape. Figuring out if we have narrow shoulders relative to our hips is a great place to start because it’s almost entirely genetic and can influence our ability to build muscle.

Do You Have Narrow Shoulders?

I initially read about this a decade ago in the old Scrawny to Brawny book by Dr John Berardi. In it, Dr Berardi suggested that if your collarbone-to-hip ratio is 1.46 or higher, then you have an ideal frame for building muscle. Digging into the research, there are indeed a few studies proving that we can use that ratio as a way of predicting our overall size and muscle mass.

Two of these studies are especially interesting.

The first is a study out of Johns Hopkins University titled Body Mass Prediction From Skeletal Frame Size in Elite Athletes. In this study, the researchers took elite athletes who competed in various sports, measured their collarbone-to-hip ratio, weighed them, and established a way to predict body mass based on bone structure.

The strength athletes, such as the Olympic weightlifters, were the broadest and most muscular, with a ratio of 1.5. These are the mesomorphs, and they really are naturally bigger and stronger. The endurance athletes, such as the decathletes, were the narrowest and thinnest, with a ratio of 1.3. These are the ectomorphs, and again, they really are naturally thinner.

A follow-up study titled Body Mass Prediction From Stature and Bi-iliac Breadth in Two High Latitude Populations confirmed the findings from Johns Hopkins, but more importantly, proved that the findings were applicable to the general population, not just elite athletes. They found that the Inupiats (aboriginals of Alaska) have a 1.38 collarbone-to-hip ratio and are slenderer than Finns, who have a 1.41 ratio (study).

In both studies, the researchers found that these body type differences were predictive, meaning that by taking these shoulder and hip measurements, we can get an idea of how big and muscular we can naturally get. All body types can build muscle, but guys with a more mesomorphic bone structure are going to have a slightly higher muscle-building potential than guys with a more ectomorphic bone structure.

Measuring Shoulder Width

If you want to figure out whether you have a mesomorphic or ectomorphic frame, you can measure the length of your collarbones (bi-acromial breadth) and then divide it by the width of your hip bones (bi-iliac breadth).

To do that, you need to make sure that you’re measuring the width of your bone structure, like so:

Bony to Beastly Bone Structure V-Taper Ratio

To figure out how long your collarbones are, use a measuring tape to measure the distance between the outermost parts of your shoulder bones. This doesn’t include your upper arm bone or your shoulder muscles, but just where your shoulder joint begins. Also, keep in mind that we’re measuring the distance between the joints, so hold the measuring tape out a little bit in front of your body so that it doesn’t curve around your chest.

Then do the same thing with your hips, measuring between the outermost part of your upper hip bones, again without bending the measuring tape.

Once you have these measurements, divide your collarbone length by the width of your hips to get your ratio.

Bone Breadth Ratio = collarbone length / hip width

  • If you have a ratio under 1.4, you have a more ectomorphic body type
  • If you have a ratio of 1.4–1.45, you are average
  • If you have a ratio of 1.46–1.5, you have a more mesomorphic body type

Examples of Men with Broad and Narrow Shoulders

For an example of someone with amazing natural muscle-building potential, we can look at the classic bodybuilder Steve Reeves. Even as a young teenager, you can see that his collarbones are quite broad and his hips are quite narrow:

Muscle-Building Genetics, Bone Structure V-Taper, Steve Reeves

However, even ectomorphs can build impressive amounts of muscle mass, especially if their goal is just to look strong, healthy, and attractive.

A couple of good examples of that are Ryan Gosling and Brad Pitt. Both have ectomorph body types, but Ryan Gosling has a narrower ectomorph build, whereas Brad Pitt has a slightly broader ectomorph build. If you’re an ectomorph, chances are that you’re somewhere in the middle.

Ectomorph Actor / Celebrity Genetics Ryan Gosling & Brad Pitt

How Does Shoulder Width Affect Muscle Growth?

The research from Johns Hopkins shows that ectomorphs naturally carry less muscle mass than mesomorphs. However, if your goal is to become strong, muscular, and healthy, it won’t make as much of a difference as you might expect.

Most research shows that our muscular genetic potential is only about 5–10% lower than the average man’s. And since hardly anyone gets anywhere even close to their genetic potential, that’s hardly any limit at all.

For example, if you look at Ryan Gosling and Brad Pitt above, both of them are ectomorphs, and neither of them is anywhere near his natural muscle-building potential. If you want, you can become far bigger and stronger than either one of them.

If you’re curious about how big and strong you can get, and how quickly you can do it, here’s our article on ectomorph muscle and strength potential.

Are You A Hardgainer?

The original hardgainer test had to do with the thickness of our bones. In the 1950s, the famous bodybuilder Reg Park began noticing that “the small-boned type” didn’t build muscle as easily as other body types. Because they didn’t gain muscle as easily, they were dubbed hardgainers.

Reg Park wasn’t a scientist, mind you. He didn’t actually measure anyone’s bone thickness, and he didn’t prove a causal link. It was just an observation. It sparked a line of research, though, and a couple of decades later, Dr. Casey Butts found that there is indeed a relationship between bone thickness and muscle-building potential.

Now, before we talk about Dr Butts’ bone-thickness research, it’s important to talk about a common misunderstanding about skinny guys and hardgainers.

Skinny Guys Tend to Gain Muscle Faster

However, there isn’t a link between bone thickness and the rate of muscle growth. In fact, guys who are naturally thinner tend to gain muscle more quickly than average. This is because skinny guys are further away from their genetic limit, allowing them to gain far more muscle before running into the law of diminishing returns.

Illustration showing that skinny ectomorphs can build muscle more quickly than other body types.

Because we’re starting underweight, many of us skinny guys are able to make remarkable “newbie gain” transformations. Here are some examples of skinny guys quickly building muscle.

Hardgainers Have Trouble Gaining Weight

There’s also research showing that some people resist weight gain. For example, in a famous 1999 study, the researchers overfed people by 1000 calories and measured how much weight they gained. Some of the study participants gained as much as 9 pounds, whereas other participants gained less than a single pound. This landmark study proved that some people have a harder time gaining weight than others.

Illustration of a skinny hardgainer eating a feast in his attempt to bulk up, gain weight. and build muscle.

For example, in a famous 1999 study, the researchers overfed people by 1000 calories and measured how much weight they gained. Some of the study participants gained as much as 9 pounds, whereas other participants gained less than a single pound. This landmark study proved that some people have a harder time gaining weight than others.

Although hardgainer was initially used for people who have a hard time building muscle, that’s now been replaced with the term “non-responder.” The term hardgainer now usually refers to someone who has a hard time eating enough calories to gain weight. (We’ve got a full article on hardgainers.)

So as skinny guys who are trying to bulk up, we’ve actually got the potential to build muscle very quickly, but we also tend to have an incredibly hard time eating enough calories to do so. Here’s our guide for eating more calories.

Do You Have Thin Bones?

Dr Casey Butts’ research found that guys with thinner bones can support less muscle mass on their frames. As we mentioned above, this doesn’t have much impact on a skinny guy’s ability to build muscle. In fact, we can often build muscle more quickly than others.

However, the thickness of our bones will impact how muscular we can ultimately become. Given that the weight of our bones impacts our body weight, having thinner bones can also mean that we weigh less overall even when we have a comparable degree of muscularity to other people.

Measuring Wrist Thickness

To see if we have proportionally thin bones, we need to measure how thick our bones are and then compare that to our heights. The best place to measure your bone thickness is in your wrists and ankles because, unless you’re extremely overweight, those measurements are determined almost entirely by the thickness of our bones.

Wrist size is most closely related to arm muscularity, whereas ankle size is more closely linked with leg muscularity. Most guys don’t really care about how muscular their legs are, so we’ll use wrist size.

Bone Thickness Ratio = Wrist Circumference / Height

To find out whether you have an ectomorphic bone thickness, measure your wrist circumference and then divide it by your height (in cm or inches). If the number you get is smaller than 0.1045, you have thin wrist bones, which is a sign that you’re an ectomorph.

To figure out what an exceptionally thick bone structure is, Dr Butts took the wrist and ankle measurements of bodybuilders from the 40s and 50s, before steroids were available. For example, the thinner bodybuilder Ron Lacy (Mr. America 1957) had a moderate ratio of 0.1058, whereas the thicker bodybuilder John Grimek had a ratio of 0.1138.

Dr Butts compared the bone size of every single famous natural bodybuilder against their muscularity to see if there was a correlation between bone width and overall muscularity.

After measuring the proportions of hundreds of bodybuilders, Dr Butts found that men with a ratio of 0.1111 or greater were able to build substantially more muscle than the average guy. Their genetic muscular potential was about 10% higher. He called these guys “easygainers,” but that term never really caught on. We’ll refer to these guys as mesomorphs instead.

To be clear, a 10% increase in genetic muscular potential isn’t much for the general population. Most people never reach their genetic muscular potential anyway, and once a guy looks strong, he reaches a point of diminishing returns, where becoming even bigger and stronger won’t make him any healthier or more attractive.

By the time a guy can deadlift 400–500 pounds, squat 300–400 pounds, bench press 250–300 pounds, and curl 135 pounds, becoming even stronger isn’t going to have a big impact on his health or appearance. This means that this upper limit of muscularity is really only relevant for strength athletes, bodybuilders, and powerlifters. In that case, it’s best to be a mesomorph.

Bony to Beastly Ectomorph / Hardgainer Genetics Skinny Wrist Size

Anyway, moving back to our body-type tests, we’ll use a ratio of under 0.1045 to denote an ectomorph body type and a ratio of over 0.1111 to denote a mesomorph body type.

  • If your ratio is over 0.1111, you have great muscle-building genetics
  • If your ratio is 0.1045–0.1111, you have average muscle-building genetics
  • If your ratio is under 0.1045, you’re an ectomorph

However, we quickly realized that not a single member of our community had a ratio that was even over 0.1. We aren’t just ectomorphs, we’re extreme ectomorphs.

For example, my wrist circumference is 6.5” and my height is 74” (6’2), making my ratio 0.088. With wrists this small, I’d still be classified as an ectomorph even if were only 5’4 tall.

I reached out to Dr Butts to ask about this, and he told me that having an exceptionally thin bone structure is rare enough in the bodybuilding community that his calculations can’t account for it. He predicted that we’d likely be able to exceed his predictions of muscularity. He was right, too. Many of us have, myself included.

This goes to show that if you’re on the extreme side of being an ectomorph, the calculators that predict muscularity aren’t calibrated for you, and so they might underestimate your muscle-building potential.

Does Having Thin Wrists Make it Harder to Build Muscle?

According to the research of Dr Casey Butts, having thin wrists is linked to a 5–10% decrease in muscle-building potential. However, this doesn’t affect our rate of muscle growth, it just means that we’ll reach our genetic muscular potential at lower body weights.

Given how few people reach their genetic limit, this shouldn’t be a big issue. However, it might mean that you need to train for muscle mass more deliberately than guys who are naturally more muscular. For example, guys with thicker bones often carry more muscle mass by default, and so they may be able to maintain a pleasantly muscular physique just by doing cardio. An ectomorph, on the other hand, may need to bulk up with dedicated hypertrophy training in order to become strong and healthy.

Sometimes having thinner bones is a disadvantage, such as when trying to fill out the sleeves of a t-shirt, maintain a healthy posture, avoid concussions, or avoid broken bones. As such, again, we tend to benefit from lifting weights, which is going to fill out our frames with muscle mass, make our bones denser, strengthen our posture, and protect our spines.

Sometimes having thinner bones is an advantage. We have the potential to be quite strong and athletic for our size, being fairly light even after gaining quite a lot of muscle. That’s a great asset when it comes to running, doing bodyweight exercises (such as chin-ups), or playing sports with weight classes.

Ectomorphs May Be The Most Attractive Body Type

Another benefit is that men with thinner bones are often considered more attractive to women. To test this idea, we surveyed over 500 women, showing them the bodies of celebrities with a range of different body types.

The results of our survey showed a clear preference for ectomorphs who had succeeded in building muscle, with Brad Pitt’s Fight Club Physique being rated as the most attractive male physique.

Brad Pitt's ectomorph body in fight club was rated by women as being the most attractive male body type.

The most famous Hollywood actors are all ectomorphs, too. They all have narrower bone structures. This is true with guys like Johnny Depp and Leonardo DiCaprio, although you could argue that has little to do with their physiques, and you’d probably be right. They’re mainly known for having attractive faces and personalities.

What’s more interesting is that when you consider the actors who are known for having the most attractive bodies, again, it’s a list of ectomorphs.

Some good examples of attractive actors are Ryan Gosling, Brad Pitt, Cam Gigandet, Paul Walker, and Michael Fassbender, all of whom have thinner, ectomorph bone structures.

Ryan Gosling, Brad Pitt, Cam Gigandet, Paul Walker, Michael Fassbender Bodies & Ectomorph Genetics

Ectomorphs are often rated as the most attractive body type outside of Hollywood as well. The top male models have thin bone structures, and many of the athletes who are considered attractive have ectomorph builds as well. Take a look at the top male model Mr. Ward and the soccer player David Beckham:

Mr. Ward and David Beckham Ectomorph Hardgainer Genetics

How Full Are Your Muscle Bellies?

The third and final ectomorph test has to do with the relationship between our muscle bellies and our muscle tendons.

Most people know that lifting weights can make our muscles thicker, making us bigger and stronger. But most people don’t know that lifting weights can also make our muscles longer, improving our strength and flexibility.

No matter how much we lift, though, we cannot change the length of our muscles in relation to our tendons, which can have a big impact on how our physiques look and perform.

How to Measure Your Muscle-Belly-to-Tendon Ratio

An easy way to test your muscle belly size is by measuring how big your biceps are relative to your tendons. If your muscle bellies are smaller, it will be harder to develop big biceps, but the muscles will contrast sharply against the tendons right next to them, giving you more attractive muscle peaks.

Bony to Beastly Muscle-Building Genetics Small Muscle Bellies

To determine your muscle-to-tendon ratio, flex your arm to 90 degrees, face your palm towards your biceps, and see how many fingers you can fit between your biceps muscle belly and your forearm. (See the video for an example.)

  • If you can fit 3 or more fingers between your biceps and forearm, you have an ectomorphic muscle-to-tendon ratio.
  • If you can fit 2 fingers, you’ve got an average muscle-to-tendon ratio.
  • If you can fit 0–1 finger you have a more mesomorphic muscle-to-tendon ratio.

In the above video, you can see me easily fitting three fingers between my biceps and forearm, slotting me firmly in the ectomorph category. With bodybuilders and fitness models, this is quite rare. However, when you look at guys a little further away from bodybuilding, you see far more famous ectomorphs. Some top tier actors, like Ryan Gosling and Brad Pitt, are ectomorphs who have very small muscle bellies.

Brad Pitt & Ryan Gosling Hardgainer / Ectomorph Muscle Belly Genetics

What Does Having Small Muscle Bellies Mean?

The main place that guys notice smaller muscle bellies is in their biceps. It’s not that it looks bad, it’s just that their arms tend to start off looking lankier, and often require some extra isolation work in order to fill out a shirt sleeve.

Some guys can get away with growing their arms with compound lifts, but you probably aren’t one of them. If your arms are naturally lankier, build your routine around big compound arm lifts like chin-ups (for the biceps) and overhead presses (for the triceps), but also include plenty of isolation work, such as biceps curls and triceps extensions.

Also, remember that your biceps and triceps are just a small part of your upper arms. You can add tons of girth to your arms by training your other upper-arm muscles, such as your brachialis, brachioradialis, your deltoids, and all of your forearm muscles. The best way to do this is to use a larger range of motion when doing your arm exercises:

  • When doing chin-ups, for example, start from a dead hang and bring your chest all the way up to touch the bar.
  • When doing overhead presses, bring the weight down all the way to touch your chest.
  • When doing curls, start with your arms fully extended, and bring the bar all the way up to your chin.
  • When doing rows, reach all the way down, and then pull the weight all the way up to your torso.

The larger your range of motion, the better you’ll stimulate the main movers (such as your biceps and triceps) and the more you’ll involve all of the muscles that can assist in the movement, including all of the other muscles that can bulk up your arms.

Overall Ectomorph Muscle-Building Genetics

Okay, so let’s say you have a stereotypical ectomorph body type, as I do. That isn’t bad. Yes, it might ruin your chances of becoming an Olympic weightlifter, but it also increases your odds of becoming a decathlete. Mind you, you probably aren’t trying to become a decathlete. If you’re like me, you’re probably a skinny guy who’s eager to bulk up. So learning that you have a great future as a marathon runner isn’t exactly great news.

The good news is that being strong, healthy, and attractive is different from pursuing professional sports, and we don’t have a disadvantage there. Yes, it can be harder for ectomorphs to become as strong as other body types, but it’s also much easier to stay lean.

Skinny guys benefit from lifting weights, gaining weight, and bulking up. Most other guys benefit from doing cardio and losing weight. We’re not worse off, we just have different strengths and weaknesses.

More good news: women often rate the ectomorph body type as being the most attractive. For an exaggerated example, compare the mesmorphic wrestler Brock Lesnar with the ectomorphic model Sean O’Pry (the highest paid male model):

Ectomorph Muscle-Building Genetics Brock Lesnar Body vs Sean O'Pry

Lesnar’s strong mesomorph physique is great for strength sports and bodybuilding, whereas O’Pry’s ectomorph physique not only lines up perfectly with health ideals, but most women also consider it extremely attractive.

Also, note that O’Pry isn’t anywhere close to his genetic muscular potential. Even if his genetic muscular potential were 10% lower than average (as is typical with ectomorphs), he could still gain at least another 30 pounds on top of that physique before brushing up against his genetic limits. His genetics would never be a limitation for him.

To be clear, neither body is better than the other, but each is better at different things. Given that we have more in common with the ectomorph on the right, I would recommend aiming for a body more like that. His face may not be something we can acquire, but that body is realistically achievable for every ectomorph.

In fact, given how far O’Pry is from his genetic potential, that physique isn’t all that difficult to build. It’s something you could do with a good diet and three hourlong workouts per week. It wouldn’t even take that long. A year, at most.

Bradley Cooper, Jake Gyllenhaal, Shia LaBeouf (Realistic Ectomorph / Hardgainer Bodies)

Women aren’t looking for the next Steve Reeves or Arnold Schwarzenegger, just a guy with a strong, healthy physique who will make a great father and make his family feel safe. Think more along the lines of Bradley Cooper, Jake Gyllenhaal, or Shia LaBeouf.

How Should Ectomorphs Exercise?

Ectomorphs often make the mistake of assuming that lifting weights is for guys who want to look like bodybuilders. Yes, it’s true that bodybuilders build their physiques by lifting weights, but even if you just want to build a little bit of muscle, you should still be lifting weights. After all, lifting weights is the type of exercise designed to help guys become bigger and stronger.

Hugh Jackman Deadlifting to Build Muscle

For example, Wolverine doesn’t look like a bodybuilder, but Hugh Jackman (above) was deadlifting 405 pounds to get in shape for that role. In fact, deadlifting 405 pounds is a good benchmark of strength if you want to build a visibly strong physique, as are benching 225 pounds, squatting 315 pounds, doing chin-ups with 50 pounds around your waist, and pressing 135 pounds overhead. Even for an ectomorph, all of those goals are realistic.

You don’t have to use a barbell, of course, but the same principle holds true if you’re using dumbbells. You’ll still want to hit the equivalent strength standards.

The problem is, most ectomorphs realize that their body type isn’t built for strength sports, and so they’re drawn to the types of exercise that line up with their natural strengths. They gravitate towards callisthenics, cardio, martial arts, and general physical preparedness, such as CrossFit and P90X. That can be frustrating, though, because it doesn’t help them build muscle mass, and so it fails to help them build strong, healthy, and attractive physiques.

Remember that the fitness model who represents P90X, Tony Horton, built his physique with bodybuilding before being hired to represent P90X, at which point he became a little smaller. Same thing with the callisthenics guys. Most of them build their muscle with weights before moving on to callisthenics.

Illustration of a skinny guy becoming muscular from doing biceps curls.

If your goal is to be bigger and stronger, it’s best to be deliberate about gaining size and strength. It’s best to train in a way that’s specifically designed to help you bulk up, which is called hypertrophy training.

I suspect that once you start following a good bulking program, you’ll realize that your ectomorph genetics aren’t any kind of limitation. In fact, you may even realize that you build muscle surprisingly quickly and leanly:

Bony to Beastly Ectomorph Transformation Skinny Hardgainer Genetics

To be clear, your results won’t look exactly like this. We’re all a little bit different. We all build muscle in slightly different ways. But the point is that you can certainly bulk up, and your muscle-building genetics may be much better than you expect.

Illustration showing the Bony to Beastly Bulking Program

If you want more muscle-building information, we have a free bulking newsletter for skinny guys. If you want a full bulking program, including a 5-month workout routine, diet guide, recipe book, and online coaching, check out our Bony to Beastly Bulking Program. Or, if you want an intermediate bulking routine, check out our Outlift Intermediate Bulking Program. If you liked this article, you’d love our full programs.

Shane Duquette is the founder of Outlift, Bony to Beastly, and Bony to Bombshell, each with millions of readers. He's gained seventy pounds and has over a decade of experience helping more than ten thousand naturally thin people build muscle. He also has a degree in design, but those are inversely correlated with muscle growth.

Marco Walker-Ng is the founder and strength coach of Outlift, Bony to Beastly, and Bony to Bombshell. He's a certified trainer (PTS) and nutrition coach (PN) with a Bachelor's degree in Health Sciences (BHSc) from the University of Ottawa. He has over 15 years of experience helping people gain muscle and strength, with clients including college, professional, and Olympic athletes.