Microtrauma Theory

As a result of the realization that there is no direct relationship between lactic acid and muscle growth, a new theory was developed. In this process, more than one competing theory has emerged due to the better recognition of the muscles. According to the Microtrauma Theory, one of the most basic of these:

A lot of minor damage occurs to our muscles during heavy resistance training. The initial response to this muscle damage is catabolic processes (muscle degradation) and inflammation. After muscle degradation, muscle repair processes begin. Cells called muscle satellite cells or muscle satellite cells are involved in rapid muscle recovery. They also enable the development of muscles. During this recovery, not only muscle myofibers are healed, but also extensive changes such as main vascularization, internal vascularization and renewal of the intercellular matrix are experienced. These basic postulates are also the basis of many theories developed later.


This theory draws its strength from the satellite cells found in the muscle strips of healthy adults, which can be in the order of 1–2 x 1010. Under normal conditions, these cells do not reproduce themselves; however, when major damage occurs, such as a muscle tear, or on a “micro” scale, such as during muscle work, muscle satellite cells begin to divide rapidly, differentiate and form new muscle myofibers.

This regeneration occurs through differentiation of stem cells in the bone marrow or muscles and is experienced in a very similar way to myogenesis (muscle production) during embryological development. Indeed, analyzes using various molecular markers have shown a remarkable proliferation of muscle satellite cells within 24 hours of resistance training.

Although Microtrauma Theory has a very solid foundation, it fails to explain the differences in muscle mass and amount of muscle growth between men and women. It is thought that these differences are most likely due to differences in the hormone testosterone — which puts the hand of one of the theory’s strongest opponents, the Hormone Theory. Therefore, it is useful to take a look at this theory as well.

Hormone Theory

It is clear that certain hormones and growth factors can affect muscle growth positively or negatively. For example, athletes trying to make an unfair profit in competitions may inject steroid hormones into their bodies — the notorious testosterone, a steroid hormone associated with men but also found in women. So it is clear that hormones have some effect on muscle development; however, it is not clear how exactly they play a role in muscle development or whether they are the main factor responsible for muscle growth.

Studies show that as the amount of testosterone increases, the lean muscle mass also increases. This is seen as the main reason why men have more muscle than women, and the fact that it can explain it gives strength to the Hormone Theory.


Not all testosterone in the body is accessible; A significant part of it is bound to another molecule called Sex Hormone Binding Globulin (Eng: “Sex Hormone Binding Globulin” or “SHBG for short”), another part is used by being converted to testosterone-derivatives such as dihydrotestosterone — dihydrotestosterone is one of the hormones responsible for baldness. Some of the testosterone is broken down by the aromatase enzyme and converted to estradiol and other estrogen hormones, which are more concentrated in females.

Exactly how testosterone relates to muscle growth isn’t clear, however. The most likely explanation is that testosterone reinforces the transformation of mesenchymal multipotent cells into myogenic (muscle-related) cells, restricting their transformation into adipogenic (fat-related) cells. The chemical pathway is this: Androgen hormones, such as testosterone, regulate mesenchymal multipotent cells by binding to androgen receptors (AR) in muscles. They also provide the activation of a factor called T-specific transcription factor 4 (TCF-4) by translocation of the AR-β-catenin complex to the nucleus. TCF-4 enables the myogenic transformation of stem cells by activating a group of genes known as wnt-regulated genes.

In addition, there are some findings showing that the stimulation of androgen receptors in the muscles by hormones such as testosterone or dihydrotestosterone increases muscle mass. It is also known that the frequency of androgen receptors increases in muscle builders, which may facilitate muscle growth by creating a positive feedback loop. Also, an increase in testosterone can trigger growth factors such as “insulin-like growth factors” or “IGF”, which can promote growth in general (for example, estrogen hormone has the opposite effect on IGF in some animals). appears to be). It is this testosterone-IGF connection that is the mainstay of Hormone Theory. So this theory, in summary, proposes the following kind of pathway:

  1. Muscles are stimulated by resistance exercise.
  2. Testosterone and growth hormone are secreted.
  3. Growth factors, especially IGF-1, are produced.
  4. Protein synthesis increases and the muscle becomes larger.

Although the Hormonal Theory is a strong candidate, it is not generally accepted as muscle growth is observed due to stress even after genetic silencing of the IFG-1 receptor in mice. Similarly, many muscle growth pathways associated with the hormonal activity to date have not been found to be appreciably dependent on these hormones, and the validity of this theory is therefore highly questionable.

  • Translated from evrimagaci.com ()

This article is an excerpt from by Karl Liebermann | Jun, 2022 | Medium