Just about every man on planet earth knows that testosterone is a one of the most important factors for gaining muscle, i.e. hypertrophy. And so few men would be surprised to read that studies have shown that this is very likely one of the key ways that Testosterone Therapy (HRT) improves general health for hypogonadal men: it increases fat free muscle mass, which is basically muscle. If you take a man with low testosterone and give him testosterone, it does many near miraculous things, but one of them is put on muscle.
How does testosterone work its magic? Testosterone induces muscle gains in several key ways. However, probably the most powerful way is through the stimulation of “satellite cells”. These are specialized cells that are located near the end of muscle fibers and, after a workout, they fuse together, supply nuclei, multiply and do many other things to build additional muscle fiber. Of course, this leads to a greater cross sectional area of muscle and the muscle growth that so many of us covet.
One study on senior men verified just this and found that increases in supplemental testosterone led to a dose dependent increase in both satellite calls and muscle cross sectional area.  For all your seniors out there: testosterone can help you put on muscle at ANY age. Of course, studies on healthy young men have found the same thing: the more the T, the more the muscle growth, both through increased cross secional area and increased fiber counts. 
And it’s no secret that steroid guys enjoy the dose dependent aspect of testosterone, because in this case more T usually does lead to more muscle. It also leads to more estradiol and a host of problems when go into “supraphysiological” territory, i.e. above normal, but that’s another story. The point is that testosterone has been verified in many ways to lead to muscle growth if increased enough.
If you are hypogonadal, i.e. you have clinically low testosterone, testosterone therapy at any reasonable level can REALLY help you put on muscle. Many studies have shown that testosterone therapy increases fat free mass in hypogonadal men without them doing much of anything else, i.e. limited or no workouts. This study showed, interestingly, that muscle was increased with fat levels staying the same roughly.  Of course, even with no fat loss, this will be good for long term health. The list of studies showing all of this could go on and on, but it is well-established that the more the testosterone, the more the muscle.
NOTE: Interestingly enough, as a low testosterone guy for several years (with a total testosterone level in the 280-370 ng/dl range), I was still able to put on some pretty decent muscle. However, I was very disciplined and diligent and worked out hard and watch my diet/protein levels much more than most guys. So you don’t have to have high testosterone levels for hypertrophy. Verifying this is the fact that I have had a number of younger men write in with low testosterone who were shocked because they were still able to lift phenomenal amounts of weight. My main point is this: you can get all the hypertrophy with lower levels of testosterone. However, it requires greater discipline and longer recovery times.
Common questions I get are:
“Does it matter how I raise my testosterone? Which method of HRT (testosterone therapy) will give me maximum muscle growth?”
First of all, most of the standard methods of HRT (pellets, patches topicals such as Andogel and Testim, etc.) use all bioidentical testosterone, i.e. these are not synthetic in any sense. Now the injectibles are a little more complicated and injections are quite common in HRT now for many reasons.
Injectibles are “dang near” bioidentical. Have you seen labels such as testosterone cypionate, enanthate, propionate, etc.? This is the name of an ester molecule that is tied to a bioidentical testosterone. These esters render the testosterone inactive, where it is ushered into the muscle and lays dormant until one of the body’s enzymes breaks the ester off leaving you with a bioidentical free testosterone that is ready to put you into a hypertrophic state, increase libido, pump up your brain and do all the other magic of your body’s own endogenous testosterone. The half life of the esterified testosterone is essentially related to its fat solubility, which times how fast it is released.
These esters are currently considered harmless and I have not ready of any downside. However, talk to your doc and do your own research as I always say.
I had someone write into the forum who was receiving injections yet only had testosterone of 310 ng/dl five days later, i.e. the dosage was clearly very low. Now normally injections are excellent for muscle gains if done right and, as I mentioned, most steroid guys go this route. But, if one’s dosage is too low, someone with a good prescription for patches or pellets will be superior.
Did you know you can inexpensively do your own testing for most hormones? The industry leader is Discounted Labs..
This means that one key is to make sure that you are monitored. Get your testosterone tested after going on any particular delivery system. And, if you do go on the standard injectives such as enanthate which have a short half life, realize that two weeks is quite long between injections and you will likely be low testosterone during the last half week of that two weeks. Good docs check your testosterone at about the midpoint of your whatever injections cycle you are on, hopefully weekly but some docs still do biweekly.
NOTE: For more information on how just how much testosterone can boost hypertrophy, see this link on Testosterone and Muscle. We even include an intriguing new study that claims testosterone has nothing to do with muscle growth.
Testosterone levels also taper off with pellets. If your doctor gives you too few pellets, say 10 instead of 12, and lets you go on too long between procedures, you can end up with low testosterone for several weeks. Again, this requires careful monitoring. For more information, see my links on https://www.peaktestosterone.com/ and an Interview with a Man That Loves Pellets.
Again, get tested and find out what your average testosterone levels are. Also, do not advise the “more is better” philosophy when it comes to testosterone. If you get too high, you will begin to overaromatize – just go on the steroid forums to see what this does! – and your estradiol levels will get too high, leading to potential prostate, libido and other issues. So far, the available data is showing that testosterone therapy works well as long as you stay within normal physiological ranges (unlike the steroid guys!).
What about alternative therapies for raising T, such as Arimidex and Clomid? These will definitely boost testosterone for most low testosterone men, but will they lead to significant hypertrophy? First of all, there are few direct studies on this subject with these pharmaceuticals as far as I know.
Furthermore, no steroid guy is going to take Clomid for muscle gains since the testosterones have such a proven track record and are very androgenic so we don’t have a lot of information from this crowd either. Clomid, for example, is taken by them for very specific purposes, such as reinitiating post-cycle testosterone productions or during the cycle to try to minimize testes shutdown. And Arimidex is the same: it is generally taken for to limit the overaromatization of testosterone to estrogen from the ultrahigh testosterone levels of steroid usage.
That said, there is one study on young men given Arimidex therapy that shows it did not lead to any significant change in fat free mass.  Estrogen was decreased by about half and T increased by about the same. This may sound good, but really isn’t that much of an increase in testosterone relatively speaking and so it may be that the study just did not pick up on it. Or it may be that Arimidex limits hypertrophy in ways we do not understand yet.
There is little data on Clomid and so it probably is similar to Arimidex. (For more information, see my links on Arimidex for Hypogonadal Men and Clomid and the Low T Guy.) I suspect that both Clomid and Arimidex should lead to substantial muscle gains if you are low testosterone and either of these raise your T enough. Hopefully, studies will come out that lead to more information about hypertrophy with these type of medications.
5) The Journal of Clinical Endocrinology & Metabolism, Jul 1 2000, 85(7):2370-2377, “Estrogen Suppression in Males: Metabolic Effects”