|Image 1: As a "serious" researcher you better don't use the words "testosterone" and "muscle" without "anti-doping", "hypogonadism" or "sarcopania" in one of your papers, if you don't want to risk your career.|
Testosterone, the big bad T!?
One reason for the our lack of knowledge about how (some researchers may even say "if") testosterone builds muscle certainly is a practical one. Unless you can do your research under the pretext of trying to
- treat muscle wasting disorders (associated with age, cancer, AIDS, etc.),
- invent new methods that could be useful in the WADA's antic battle against doping, or
- help infertile or hypogonodal men to a better life
Testosterone, the Jerry Bruckheimer of skeletal muscle hypertrophy?
Even if you got enough funds for your research, were not afraid to put your reputation at stake and got the approval of all the ethical committees, you would still be faced with the problem that testosterone, contrary to muscle protein synthesis, mTOR activity in tissue samples, and even the muscle specific splice variants of IGF-1, is a systemic hormone. It is (at least this is what scientists currently believe) not expressed at the tissue level (autocrine), but produced (predominantly) in your testes, from which it then carried through your bloodstream to "dock" (even that is a total inadequate oversimplification) to its receptor and... but I don't want to waste our time by going into the details of a process, of which I would assume that you have read about roughly 143x on other websites. Instead, I want to provide you with another metaphor (you know I love those), of which I hope that it will help you to understand both the complexity of the issue, as well as the current dilemma we are in.
|Image 2: The producer of a movie (here Jerry Bruckheimer at the set of PoC4, img screenrant.com) is obviously an important guy, but do you know what he does? He is important, right, but how?|
In essence the situation for scientists (and science geeks like us) looking at the "the big T" is not much different from your's in front of the film poster:
- We know that the loss of lean body and interestingly also bone mass is one of the fundamental characteristics of hypogonadism (below "normal" testosterone levels).
- We know that restoring testosterone levels to normal via hormone replacement therapy (HRT) alone will oftentimes suffice to reverse / repair the muscle loss.
- We know, or I should rather say, we like to believe that the granite hard muscle of 99% of the IFBB pro bodybuilders are built on supraphysiological levels of testosterone.
"Does testosterone build muscle?"
|Image 3: Granted, Prof. Hubert from Futurama would probably need some exogenous test, anyways. Luckily Bhasin et al. recruited young eugonadal men for their study ;-)|
Probably in view of the aforementioned "obstacles", there is only a single well-designed, and above all, extensively documented study in which researchers put our thought-experiment into practice. Obviously, the latter was no N=1 study, but involved a a group of 61 absolutely healthy eugonodal (= totally normal testosterone levels) young men (age 18-35y). Over a time-course of 20 weeks, the subjects received a weekly injection of an GnRH antagonist (to shut down endogenous testosterone production) and 25, 50, 125, 300, or 600 mg of testosterone enanthate (Bhasin. 2001). They did not exercise (in fact they were specifically advised to refrain from "strength training or moderate-to-heavy endurance exercise during the study"), did not increase their protein intake, did not co-administer any other performance enhancing drugs, yet still, they grew - well, to be precise that was the case for 3/5 of the subjects (cf. figure 1):
|Figure 1: Changes in body composition measured by under water weighing (UWW) and DEXA after 20 weeks on the given amounts of testosterone enanthate; due to a -5% decrease in the fat-free mass to water ratio in the 125mg group (all other groups draw, not lost water) the highlighted UWW value is unrealiable (data calculated based on Bhasin. 2001)|
|Figure 2: Changes in total testosterone (ng/dl) and IGF-1 (ng/ml) levels (left) and testosterone to IGF-1 ratio (right) of young eugonodal men after 20 weeks of GnHR antagonist + different doses of testosterone enanthate (data calculated based on Bhasin. 2001).|
The complexities emerge: The testosterone-IGF1 connection
If you are the intelligent reader, I suppose you are, you will already suspect that I did included the relatively minor changes of the serum IGF-1 levels for a purpose - a purpose, those of you who have followed the last last installments of this series will probably already anticipate. After all, we do now know that testosterone does build muscle, but in the previous installments we have learned that a myriad of other factors, IGF-1 included, appear to do the same.
In view of the fact that I am still bone weary from New Year's Eve and do not want to compromise the quality of this series (and don't tell me it had no quality ;-), I will take a break here and catch up on this thought... tomorrow - I mean I know that it would be unfair to put you on the racks for a whole week ;-)