How Testosterone Levels Affect Muscle Growth

It is no wonder that an average male has higher muscle mass than an average female of the same height and weight. In fact, research has proved that even with no difference in diet and exercise regimen, an average male tends to produce and grow more muscles than a female.
What drives these key metabolic components? What is the practical application of this knowledge?
The answer is pretty simple; the primary hormonal driver that stimulates the production and deposition of muscles in males is testosterone. Any disease, disorder or condition that affects the secretion or metabolism of testosterone can alter the muscle mass deposition and motor strength.
 

What Is Testosterone And How Does it Exert Its Actions?

Testosterone is the most important male hormone that is synthesized by male gonads (or testicles) under the influence of higher brain centers. Study reported in the peer reviewed journal Experimental Gerontology (1) explained the mechanism of action of testosterone in the growth of muscle mass; the key functions of testosterone are:

• Direct effect on muscles and liver to promote the synthesis of new proteins as a result of DNA activation.
• Activation and release of associated hormones and growth factors (especially insulin-like Growth Factor or IGF-1) to maintain anabolic reactions
• Activation of brain and higher mental centers for improved motor activity and muscular strength
• Testosterone increases the basal rate of metabolism; thereby generating high levels of energy that is utilized in muscle building and remodeling

In male hypogonadism (low testosterone levels), the pace of muscle synthesis decreases and fat deposition increases. Research suggests that decline in the serum testosterone secretion from 600 ng/dl to approximately 300 ng/dl can increase the rate of fat deposition by 36% (2).The muscle building effects of testosterone can be enhanced several folds by maintaining high quality diet and optimal physical activity (preferably resistance training) to further enhance the release of growth factors.
 

Dose-Dependent Effects of Testosterone

Several clinical trials and experimental studies have suggested that testosterone supplementation alone can induce muscle growth. Fred Sattler and colleagues (3) conducted a 16-week study in 112 elderly males (the age range between 65 to 90 years). The study participants were administered 5g/ day or 10g/ day of testosterone for a period of 4 months.
After the completion of the study, Sattler concluded that testosterone supplementation helped in achieving optimal serum levels of testosterone (898 ng/dl to 1046 ng/dl) during the trial which was directly associated with:

• Improvement in the lean body mass of 1.5kg
• Increase in the skeletal muscle mass of limbs by 0.8 kg
• Substantial improvement in the muscle power and strength by 30%

It is imperative to keep in mind that testosterone has the same great effect in young adult males. For example, Bhasin and associates (4) conducted an interventional study in 61 young males (between the age-range of 18 to 35 years) to study the dose-dependent response of testosterone at different concentration. For the purpose of study, the internal/ endogenous secretion of testosterone was stopped to analyze the effect of different doses.The results showed that:

• Fat mass and serum cholesterol concentration of bad lipids (LDL) is negatively related to high testosterone levels.
• Muscle power, strength and endurance is positively associated with high testosterone levels.

What Else Should You Know About Testosterone and Muscle Growth?

According to the study published in the American Journal of Physiology-Endocrinology and Metabolism (3), investigators reported that the metabolic effects of testosterone are dose-dependent. In simple words, high serum levels of testosterone are directly associated with higher lean muscle mass. But it is imperative to understand that excessive consumption of steroids (or testosterone from exogenous sources in the presence of normal serum levels may have a deleterious effect on the body in terms of cardiovascular functioning and endocrine balance.
If you are experiencing the symptoms of hypogonadism (due to aging) or acquired reasons such as a endocrine abnormality or testicular ailment, you should consult your healthcare professional regarding testosterone replacement therapy for optimal health and wellness.
 
References:

1. Oki, K., Law, T. D., Loucks, A. B., & Clark, B. C. (2015). The effects of testosterone and insulin-like growth factor 1 on motor system form and function. Experimental gerontology.
2. Bhasin, S., Travison, T. G., Storer, T. W., Lakshman, K., Kaushik, M., Mazer, N. A., … & Basaria, S. (2012). Effect of testosterone supplementation with and without a dual 5α-reductase inhibitor on fat-free mass in men with suppressed testosterone production: a randomized controlled trial. Jama, 307(9), 931-939.
3. Sattler, F., Bhasin, S., He, J., Chou, C. P., Castaneda-Sceppa, C., Yarasheski, K., … & Azen, S. (2011). Testosterone threshold levels and lean tissue mass targets needed to enhance skeletal muscle strength and function: the HORMA trial. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 66(1), 122-129.
4. Bhasin, S., Woodhouse, L., Casaburi, R., Singh, A. B., Bhasin, D., Berman, N., … & Storer, T. W. (2001). Testosterone dose-response relationships in healthy young men. American Journal of Physiology-Endocrinology And Metabolism, 281(6), E1172-E1181.