Puberty and Bodybuilding

Puberty and Bodybuilding – When can teens start gaining muscle?

when can teens gain muscle

What most teens want to know is when they can really start packing on the muscle.  They are tired of being skinny and impatient to get huge, when is the earliest you can do this naturally?

Puberty is the name given to the transition between boy and man and lots of changes occur and the hormone levels become much more favorable for building muscle. Two of the important hormones for gaining muscle are testosterone and growth hormone but there are other factors as well. Doing resistance training before testosterone is present will not results in muscle mass gain, its why 12 year olds don’t look like Arnold. Puberty is a very complex process and we are only beginning to understand the changes that take place. Lets look at the stages of puberty because it determines when you can start gaining muscle mass:

   Age     Puberty Stage  Testosterone
(% of max)
Growth Hormone
(% of max)
Strength Gain
thru lifting
Muscle Gain
thru lifting
 9-12 Height growth spurt starts, as much as 2″ a year.  Scrotum and testicles start to grow. 10% 100%  can get a bit stronger  not possible
 12-13 Height growth spurt accelerates, as much as 3″ a year.  Testicles continue to grow.  Body starts to look a bit leaner as childhood fat burns off. Light, fine pubic hair starts to grow.  75% 85%  can get a bit stronger not possible
 13-14  Height growth continues at up to 3″ per year. Pubic hair grows darker and fuller. Uncontrollable pitch changes in voice may occur, also know as “voice cracking”.  90% 80%  limited amounts  limited amounts
 14-15  Height growth skyrockets, up to 4″ a year.  Armpit hair and facial hair starts to grow.  Acne sets in.  100% 75%  fair amounts  fair amounts
 15-18  Height growth continues but slows, up to 2″ a year.  Natural muscle growth occurs (without aid of weightlifting) and body gets hairier – thighs, chest, and arms. Gentiles complete growth to full size.  100% 60%  Yes!  Yes!
 18-20 Height growth continues but slows further and natural muscle growth (without aid of weightlifting) continues.  100% 50%  Yes!  Yes!
 20-35  Prime adult years  100% 25%  Yes!  Yes!
 35-60 Golden years  80% 10% Yes limited


What does all this mean? Basically, until you have have armpit hair and facial hair, you are not going to be able to add muscle mass. For most teens, thats around 15 years of age. Lifting before then wont accomplish much in the muscle-mass department. Does this mean you should start squatting, benching and deadlifting at age 15? Maybe, maybe not, as there are other things to consider as well. Bone growth doesn’t stop till about age 20 so you still have some growth yet at age 15. The question is if you want to put these kinds of loads on a skeleton that is not yet mature. The medical profession says no, but most strength trainers ignore this advice and start deadlifting and squatting in their teens. No these lifts will not stunt your growth but injury is a concern in a skeleton that is still growing. Another issue is coordination, doing complex exercises like squats and deadlifts require a lot of coordination to perform them properly and bad form *will* cause injury. Teens are known for being un-coordinated because their bodies are changing size and proportions faster than the brain can figure out how to control everything. The last issue to consider when deciding whether to start hardcore lifting right at age 15 is maturity and judgement. For most teens, the brains are lagging behind the body in development at this time. There is a reason that the legal age for being an adult is 18 in most places in the world, its because until that time judgement skills have not fully developed. Before age 18, one is much more likely to do something stupid in the gym like lifting more weight than you can safely do just to show off. Personally, I advise waiting till your growth is totally complete, around age 20, and the coordination and judgement is under control before doing squats and deadlifts … but do your own risk/benefit analysis and decide what is right for you.

Testosterone, Growth Hormone, Puberty, and Aging

testosterone and growth hormone vs age chart

The above chart shows two of the important hormones necessary for gaining muscle mass and how they vary with age. Notice the testosterone curve, it skyrockets up starting at age 10 and peaks about age 15 then stays there till about age 35 when it starts a steady decline. Growth hormone on the other hand starts really high in young kids and then decays down to about 10%. The sweet spot for building muscle is approximately ages 15-25 when both the testosterone and the growth hormone levels are high. Please note that puberty comes at different times for different people so the age 15 is an approximation. A much more accurate start of the prime muscle building era is when you develop armpit hair and facial hair.


There are a lot of excellent reasons to exercise and in my opinion, bodyweight type workouts are beneficial as early as the early teens.  Working out helps keep bodyfat low, aides with sleep, and boosts confidence and self-esteem, something virtually every teen needs. Before the age of 15 though, there will not be any appreciable muscle mass gain. After a teen gets armpit hair and facial hair, its a sign that they are at the optimal hormonal levels to maximize muscle gain and this optimal period lasts until about age 25. Although the optimal hormonal levels exist after about age 15, that still does not mean that hardcore lifting is prudent as injury is more likely in un-coordinate, impatient teens than in mature adults. Its a risk/benefit analysis that everyone needs to do for themselves. Personally I would recommend staying with my teen workout till age 19, then taking then putting the pedal to the metal!