Muscle hypertrophy: hormones and cytokines

The increase in muscle mass occurs under the influence of several causes and is called hypertrophy. You will learn what these causes are, what dietary habits have to do with it and how hormones affect muscle growth in volume, you will find out in this article.


  1. General information.
  2. Types.
  3. Satellite cells.
  4. Hormones and cytokines.

General Information

The simplified version for those wishing to increase muscle mass of the body says that it is enough to make a proper training schedule with physical activity, and the result will not be long in coming. It is overlooked that physical factors mediate metabolic stress, nutritional regimen, and hormonal influence. Initially, in untrained people strength training gives a feeling of strength solely due to nervous influences, but after a couple of months, hypertrophy becomes the result of physical activity.

Muscle mass gain is influenced by:

  • heredity;
  • gender;
  • age;
  • the nature of the diet;
  • type and proper organization of training.


To understand muscle hypertrophy, we must learn to distinguish it from muscle hyperplasia. In hypertrophy, the contractile components and intercellular substance, which acts as a matrix that supports cell growth, increase. Hyperplasia is an increase in the number of muscle fibers.

Hypertrophy is the result of a series of myogenic events, which eventually lead to an increase in the size and number of myofibrillar contractile proteins: actin and myosin, and the total number of sarcomeres arranged in parallel. In turn, this process increases the diameter of individual muscle fibers and leads to an increase in the cross-sectional area of muscles.

There is a fundamentally different type of hypertrophy – sarcoplasmic hypertrophy – due to the increase in various noncontractile elements and fluid. Such increase of muscle mass is achieved without any special physical efforts. Sarcoplasmic hypertrophy is non-functional and its essence is swelling of muscle fibers related to protein metabolism, the activation of which leads to greater growth of contractile tissue.

Satellite Cells

Muscles are postmitotic tissues and are not permanent cells, changing throughout life. Muscle hypertrophy is a kind of key to preventing apoptosis of cells, preventing their age-related degeneration, atrophy. This state is achieved through a dynamic balance between protein synthesis and decomposition. Hypertrophy occurs if synthesis exceeds protein breakdown.

It is a link between the satellite cells, which are located between the basal membrane and the sarcolemma. These myogenic stem cells are usually immobile, but are activated by mechanical action on the skeletal muscle. Upon awakening, they divide and fuse with already existing cells or interact with each other to create new muscle fibers.

Satellite cells affect hypertrophy in several ways:

  • donate additional nuclei to muscle, increasing the synthesis of new contractile proteins;
  • increase existing muscle mass;
  • help repair damaged muscle.

Hormones and cytokines

Any hypertrophy is impossible without regulation of anabolic processes in organism. This requires a whole program of special nutrition, ensuring sufficient intake of proteins, fats and carbohydrates, but most importantly – ensuring the prevalence of protein synthesis over all others.

This is where hormones play a special role, including leptin, which controls human eating behavior and prevents the gain of extra pounds at the expense of fatty tissue and caloric foods. Its action is blocked, it becomes the background, recedes into the background. And in the center of the processes taking place are anabolics, which control protein synthesis.

Hormones are assisted by cytokines and are affiliated with interleukins and insulin. Insulin, in turn, is mediated by the same leptin. The pancreatic hormone has anabolic properties with more effect on proteolysis than on enhancing protein synthesis. It also induces mitosis and differentiation of satellite cells. Considering that insulin levels decrease with exercise, the balance between anabolics, insulin and leptin mediated by it is very important.

Exercise provokes acute and sometimes chronic changes in the hormonal background, which itself plays an important role in muscle hypertrophy.

There are three of the most studied hormones involved:

  • insulin-like growth factor;
  • testosterone;
  • growth hormone.

We should emphasize the affiliation of all of the above hormones with leptin. This is understandable: it is impossible to build up any chains regulating protein synthesis without guaranteeing sufficient protein intake into the body. In other words, nutritional behavior is above all the processes that contribute to hypertrophy of muscles.

Insulin-like growth factor (IGF-1)

IGF-1 is the main anabolic hormone responsible for the body’s response to physical exertion. It is a peptide hormone similar in structure to insulin. The hormone receptors are localized in active satellite cells, myofibrils and Schwann cells. During exercise, muscles synthesize a more systemic version of the hormone than the liver, as well as use the hormone already circulating in the bloodstream. In addition to the systemic forms of the substance, there is also the connective form. All three variants of the hormone affect the growth of muscle tissue, but the exact mechanism of this action is still unknown.

Nevertheless, the insulin-like growth factor provokes hypertrophy in the autocrine and paracrine systems, exerting its influence in several ways:

  • directly stimulates anabolism by increasing the rate of protein synthesis in differentiated myofibrils;
  • activates satellite cells and serves as a link for their proliferation, differentiation;
  • increases the fusion of satellite cells in muscle fibers, giving myonuclei.

Insulin-like growth factor also stimulates the expression of L-type potassium channel genes, which leads to the activation of a number of anabolic calcium-dependent pathways.


This hormone is a cholesterol derivative and significantly affects muscle tissue. It acts as an anabolic and plus it contacts neuronal receptors, increasing the amount of mediators released, regenerating nerve cells, and increasing the size of the cell body. The hormone is synthesized and secreted by the Leydig cells of the testes and through the hypothalamic-pituitary system – in the ovaries and adrenal glands.

In the bloodstream, tetsosterone is bound to albumin or to a steroid hormone that binds proteins. A minimal portion circulates freely, although only it is biologically active and available for tissue use. However, bound testosterone is rapidly activated by separating from albumin. The free hormone contacts the androgen receptors of the target tissues, which are located in the cytoplasm of the cells. This helps transport the hormone into the cell nucleus and its interaction with chromosomal DNA.

Testosterone is multidirectional:

  • activates protein synthesis and inhibits protein breakdown;
  • indirectly stimulates the release of other anabolics into the blood (growth hormone, for example);
  • promotes replication and activation of satellite cells.

Training correlates hormone levels with muscle cross-section. But there is still no clarity on the cumulative effect of testosterone under strength.

Growth Hormone

Somatotropic hormone (STH) is a polypeptide with both anabolic and catabolic properties. It is affiliated with leptin and affects fat metabolism, leading to triglyceride mobilization. It also stimulates cellular uptake and incorporation of amino acids into various proteins, including muscle. It also binds to insulin-like growth factor by activating its RNAi. The hormone is produced by the anterior lobe of the pituitary gland and is injected into the bloodstream in pulsating portions during sleep. There are about 100 known isoforms of the biogen that activate muscle, immunity, bone formation, and tissue fluid volume. The concentration of STH in the bloodstream increases sharply after physical activity and correlates with the magnitude of muscle hypertrophy.

Recommended Articles