Three of the primary anabolic hormones that are involved in human muscle growth are testosterone, growth hormone and insulin-like growth factor. There are other factors at play here such as insulin and thyroid hormones, but I will mainly focus on the three primary anabolic ones in a 3-part series here on my blog.
What is Testosterone?
Testosterone is the primary androgen hormone that interacts with skeletal muscle tissue in both men and women. Some individuals may not realize that women too have free-floating testosterone in their blood streams, but they do. They certainly do not have the same levels that men do, but it is present and biologically interacts the same way as men for muscle growth.
When most people think of testosterone, their minds may immediately think of "pumped" weightlifters (see picture above) that have been taking steroids. Yes, testosterone is a well-documented and well-studied anabolic steroid that has been used in the past for muscle growth, but the focus on this blog is about the naturally-occurring testosterone in our bodies. In fact, the direct effects of testosterone on skeletal muscle growth has probably been most notarized from experiences and studies conducted with steroid use but in actuality insulin-like growth factors (IGF's) have a more dramatic effect on the human body (discussed in Part 3 of this series).
Biological Interactions
Testosterone has many direct and indirect effects within the human body. Indirect interactions with other hormones demonstrate the remarkably complex neuroendocrine-immune system in influencing skeletal muscle size and strength. An example of indirect influence on the body would be testosterone's interaction with the neuron receptors. It can interact with receptors on neurons, increase the amount of neurotransmitters, and influence structural protein changes. To explain these changes to a laymen; this means that testosterone can indirectly alter muscular size and force properties of a muscle, but not necessarily both at the same time.
Many factors come into play when studying the size of an individual's muscle, but size does not necessarily correlate to the force that can be generated from said muscle. By increasing the number of neurotransmitters, for example, one can increase a muscle's affinity for force production without necessarily becoming "big". Real-world applications of this can be seen in Major League Baseball pitchers. Many pitchers can generate tremendous force from their shoulder but do not necessarily have large shoulder muscles.
Testosterone also has direct interactions on the body. It can promote growth hormone responses in the pituitary gland which can influence protein synthesis in muscle.
How Does Testosterone 'Work'?
Testosterone is secreted from the testes in men and the ovaries and adrenal glands in women. From here, it is transported to target tissues by transport hormones in the blood. At the target tissue, testosterone enters the cell membrane and directly interacts with the DNA to increase DNA transcription. This is the stage at which protein synthesis is induced and muscles cells can divide.
Testosterone can also bind to cell membrane receptors, although this field of study in to what these interactions actually do is continually growing.
Anaerobic vs. Aerobic Exercise Effects on Testosterone
Anaerobic exercise (resistance training) has consistently shown increases in blood testosterone in both men and women. This is obviously due to the effects of the type of training and therefore the biological response to increase protein synthesis in the muscles but to also increase the indirect effects on the body discussed earlier.
High-intensity aerobic endurance exercise has also been shown to increase blood concentrations of testosterone in both men and women. This may be contrary to some people's current knowledge but there seems to be a definitive reason for this. While anaerobic training may increase testosterone levels to increase protein synthesis, aerobic training causes a catabolic state in the body (tissue loss) and higher levels of testosterone may be present to simply try and keep up with tissue loss, or in other words, trying to replace the tissue that is lost. In fact, studies have shown that oxidative stresses placed on the body during high-intensity aerobic exercise may actually promote a decrease in muscular fiber size to improve oxygen transport to the cells.
Increasing Testosterone Concentrations
-Large muscle group exercises (deadlift, power clean, squats)
-Heavy resistance (85-95% 1RM)
-Moderate to high volume of exercise, achieved with multiple sets or multiple exercises
-Short rest intervals (30-60 seconds)
-Tyler Robbins
B.Sc. CSCS
Sources:
Baechle, Thomas R. and Earle, Roger W. Essentials of Strength Training and Conditioning Third Edition
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