I’m tall, lean, and just can’t seem to build any muscle mass

Last updated on August 23, 2020


Hi, my question is about bone growth (expansion) and “filling out” during puberty.

I’ll give you a summary of my development to this point. I’m a 20 year old male and will soon be 21, in the spring. I’m fairly tall (about 6’2) and I haven’t seen a change in height in over a year. I’ve been working out and exercising since I was around 16; however, I stopped recently because I haven’t noticed any muscle gains in over a year. (It feels like my frame won’t support any more muscle at this point.) Despite being tall, I only weigh about 175 lbs. My body looks very slim, especially my lower legs, forearms, wrists and fingers, which are long but slim. My torso is also rather thin (I have a 41″ chest and a 30″ waist).

I started to gain height when I was around 16-17 and was finished by the time I was 19. My shoulders have started to widen a bit, but they are still somewhat narrow. When I was around 18, I was eating a lot and became somewhat chubby (about 210 lbs). Shortly after I turned 19, I slimmed down considerably. I was doing rigorous cardio exercise for 30-45 minutes everyday and I was also eating less – around 1600 calories – I did this for about 2 and a half months and slimmed down to around 170 lbs. My voice is consistently deeper and I have a prominent Adam’s apple, which I began to notice when I was around 19 and a half. I first noticed facial hair on my chin when I was 18 and a half; however, in the last 4 months it has become thicker and coarser on my chin, upper lip and side burns. I’m still a long way from a full beard, though. I have pretty thick underarm hair and my pubic hair is fully developed (it grows on my inner thighs). In the last few months, I’ve also noticed increased hair growth on my feet and toes. My chest size has increased, but I’ve been doing lots of push ups for the last year or so. Also, my chest expanded outward, as opposed to widening. I developed bad acne around the time when I turned 19, but it has almost completely disappeared. I was on Accutane for about 6 months, until I turned 20. My scrotum hangs down, my penis appears to be fully developed, its size increased slightly about a year ago, and my testicles are adult size, a little over 2 1/4 inches.

I’m wondering when bone growth or expansion occurs and when I will “fill out”. I look like a tall 15 year old and I find this extremely frustrating. It’s also been very discouraging to work out and see little to no gains. I feel like I’m powerless to change myself. I’m particularly curious about bone growth, since I feel like my “frame” is responsible for my situation (I haven’t really widened at all). I know I’ve haven’t experienced any bone growth yet. I’ve been self conscious about this for a while. As I mentioned earlier, my wrists and fingers are very slender. My wrists measure 6″ around, and my pinky finger could be mistaken for a 3 year old’s index finger. From what I understand, wrist and finger size are the primary measures for determining bone width. With the exception of the short period when I wasn’t eating much in order to lose weight, I eat well. My father is slightly shorter than me, however he is much bigger. His wrists measure roughly 9″ around. Even my mother’s wrists are slightly bigger than mine, so I’m relatively sure genetics aren’t the issue. I talked to my doctor and he had a blood test done for hormones and a bone age test – both of them were normal.

I’m very sorry for the long email, but I’d really like to know what’s going on and when I might see some changes happening. As I said, this is really frustrating for me and I feel like a kid. Thanks for any information or advice that you can pass on!


The one thing I noted is that you were a late bloomer; that is, you developed later than the average. Judging from the time of your growth spurt you were running about three years behind the average. One of the things noted in the medical literature is that late-bloomers, also known as those with delayed puberty, tend to have narrower shoulders. While the cause is not known, my suspicion is that when a boy develops later in life, he tends to finish sooner. Since the shoulders are one of the last features to develop, the growth plates close down before shoulders get wide.

Most of what people call “filling out” is the development of muscle, not bones. You mentioned that your bone age test was normal, but you did not state what stage it placed you in. For example, if it was normal for your age, then likely it showed that you are in stage 5, which is where most young men are at your age. If so, then your growth is basically done. The growth plates would be closed off and they cannot be reversed.

There are some medical concerns when a young man doesn’t seem to be able to gain muscle mass. One of them is low levels of testosterone and other androgen hormones. However, you had blood work and these came back normal, so I am assuming that testosterone was one of the things measured and those low levels aren’t a cause for concern. Besides, low levels of testosterone are usually accompanied by little body hair.

Given that you are running about three years behind the average, you are just now at the point where muscle development should be noticeable. However, there are some men who just never get bulky because of their genetics. While it is not true with your dad or mom, you also need to consider your grandparents as well. You might have inherited a trait to be slim which is recessive. Recessive traits appear to skip generations since the dominant trait overshadows the recessive trait.

I suspect that you inherited a body type that weight trainers called “ectomorphic.” An ectomorphic body tends to be taller than the average, longer limbs, with a thin angular face. They tend to have trouble gaining either muscle mass or fat since they have a faster than average metabolism. If they gain weight, they lose it very easily. These are the type of people others are amazed to watch while they eat because they appear to be able to eat large quantities of food and never seem to gain much weight.

People of this body type tend to make good distance runners because they build more fast-twitch muscle, which is thin, than the slow-twitch muscles, which are bulky. Combined with a lighter frame, they can move faster than others. Thus they are better at sports where speed is more important than power.

If this seems to describe you, then eating a balanced diet is more important for you than for other men. Your higher metabolism means you will “burn off” your muscles if you don’t have adequate nutrition available.

For a good description of the various body shapes, see: The Three Somatotypes (Body Types).