Welcome to bodybuilding’s version of the classic “chicken or the egg” paradox. It’s well known that elevated testosterone levels can help you pack on slabs of muscle, but is the inverse true as well? Does building muscle by itself directly increase testosterone?
There are plenty of factors to consider here, so let’s dive right in.
How is Testosterone Produced?
In males, the vast majority (~95%) of testosterone is produced by the testicles. After all, the roots of the word (“testis” and “sterol”) lead to a literal translation of “testicular steroid hormone.” In short, the hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) by the pituitary gland. LH then increases specific proteins in the Leydig cells of the testicles and voilá, you have testosterone.
In females, even though they only produce about 5-10% of the amount of testosterone a male does, the beginning of the process is quite similar: the pituitary gland is stimulated to release LH & FSH. From here, LH binds to Theca cells in the ovaries, which produce androgens (such as testosterone). This accounts for about half of testosterone production for a female; the other half is derived from the adrenal glands, which produce precursor hormones like DHEA and androstenedione, which are then converted to testosterone in certain tissues.
In healthy males, roughly 4-9 mg of testosterone is produced by the testicles per day; by extension, females likely have less than a milligram of testosterone produced daily. It’s worth noting that testosterone production in males is regulated by a negative feedback loop, meaning testosterone production is stimulated in the manner described above until a certain threshold is met. Once that level is met, the hypothalamus stops signaling the stimulation of the pituitary gland to release LH/FSH and the whole “stream” shuts off from there.
In general, testosterone production peaks overnight, while you’re asleep.
So as we can see here, muscle mass is not directly implicated in either downstream signaling cascade mentioned above for male or female testosterone production. However, there are several indirect ways building muscle (and therefore strength training) can increase testosterone levels.
Strength Training and Testosterone
Several studies have shown an increase in natural anabolic hormone levels, including testosterone, as an acute response to a strength training session [2, 3]. However, this spike in testosterone generally lasts about 30 minutes, and these short-lived peaks haven’t been shown to meaningfully contribute to additional systemic muscle growth over time. At the end of the day, muscle growth is going to be influenced locally, primarily by the amount of mechanical tension you put on a specific muscle via your training routine.
Besides, you’re not building an appreciable amount of muscle mass in any single training session anyways, so it would be incorrect to think that this short-term spike was caused by “new muscle tissue.”
However, in studies comparing high-frequency training protocols to low-frequency ones, the high-frequency groups are found to have a higher resting level of testosterone after three to four weeks .
Weeks is a much longer timeframe than 30 minutes, so what gives?
Again, same as with a single session, you’re likely not building a ton of tissue in roughly a month’s worth of time, so the idea that muscle tissue itself is directly causing a higher testosterone level is still misguided. But one hormone-related mechanism of action at work here involves the ratio of testosterone to cortisol in your body, known as the T:C Ratio.
The T:C Ratio
Testosterone’s dreaded agonist, cortisol, sets the stage of tissue breakdown when its present in the body in high amounts, whether due to psychological stress, physiological stress, or both. The edge that the high-frequency groups had in the studies referenced above was a more favorable improvement of the T:C Ratio over time, with cortisol rising to a lesser extent than in the low frequency groups.
This likely indicates that the low-frequency groups were creating too much physiological stress with their lengthier training sessions than the more frequent, but consolidated training bouts in the high-frequency group. With the T:C Ratio being frequently used as a marker for tissue anabolism over time, it stands to reason that if we were to extend these study periods out for longer, the higher-frequency groups would also build more muscle due to a more favorable hormonal environment overall.
Here again, we have a somewhat circular relationship between muscle mass and testosterone, where gaining the muscle mass itself wasn’t causing the increase in testosterone as much as it is an indicator of a positive hormonal environment where cortisol is kept at bay to allow testosterone to do its thing.
Since muscle growth and hormone levels are both impacted by the training stimulus you receive from strength training, you can’t exactly separate the two out. But by constructing an effective training program, you’re going to both increase muscle mass and improve testosterone levels/the T:C Ratio over time.
And while it’s much more accurate to say increasing testosterone increases muscle mass, in practical terms, you’re also going to see the people with the most muscle mass generally having the highest levels of testosterone, because the same diet and training they’re using to build the mass in the first place is also going to optimize their hormonal profile and overall health.
Other Indirect Benefits of Muscle Mass on Testosterone
Gaining muscle via strength training can have additional knock-on effects to the overall concentrations of hormones in your body. For example, Interleukin-6 (IL-6) is a signaling molecule that can be both pro-inflammatory or anti-inflammatory in the body. IL-6 produced by fat mass creates high levels of chronic inflammation, which has been linked to low testosterone levels over time. Conversely, IL-6 produced by muscular contractions during strength training is actually anti-inflammatory, and thereby beneficial to your testosterone level.
You can’t build muscle mass without muscular contractions, either, so once again we find muscle and testosterone as part-in-parcel.
Another example: gaining muscle mass directly increases your metabolic rate, largely due to the fact that tissue anabolism is energetically expensive, as is maintaining that newly built tissue. Test subjects with more muscle mass can expend up to 15% more energy at rest than equally-lean but non-muscular subjects.
Once again, the vehicle getting you here is strength training, which is going to be the stimulus that initiates tissue growth and preservation. Conversely, a higher metabolic rate means you’re expending more energy, and if you’re consuming enough protein and training often enough to at least maintain your muscle mass, this means you’re going to be burning off other stored energy, namely fat mass.
This whole scenario leads to improved body composition over time. Specifically, losing fat mass (thanks to an improved metabolism via muscle gain) likely means that you convert (or “aromatize”) less androgens like testosterone into estrogen, which will free up more of your circulating testosterone to act in its intended anabolic manner.
Insulin sensitivity/nutrient partitioning also improves in response to strength training, meaning the energy you consume is more likely to be burned off as opposed to being stored as fat tissue. Long term, this acts as a preventative measure for fat regain, which we just learned will cut down on estrogen conversion and lead to a more anabolic environment.
In sum, since the amount of muscle you gain is going to be dictated by the amount of stress you put on your tissues via training and the resulting hormonal environment in your body, gaining muscle mass is going to be extremely closely associated with testosterone levels. The real driver of this bus is your training (and, to a slightly lesser degree, your diet), and both your muscle mass and testosterone levels are along for the ride in the right direction.
Put another way, you’re not going to come across a massive guy who gained a ton of muscle mass (naturally, that is) and find he has low T; testosterone levels need to be heightened and unabated by cortisol and inflammation for that muscle mass to exist in the first place.
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