Mechanisms of action of BCAA
BCAA as an energy substrate
Performing physical exercises increases the oxidation of BCAA and in order to maintain energy homeostasis by converting it into an easily accessible source of energy – glucose. Studies show that during and after exercise, the concentration of BCAA amino acids (especially leucine) decreases in athletes, immediately followed by metabolic processes that are aimed at normalizing the concentration of BCAA amino acids, that is, muscle proteins begin to break down as the main sources for replenishing the BCAA amino acid pool. Additional intake of the amino acid BCAA in the form of supplements can restore their concentration, and stop the process of muscle destruction.
In addition, recently scientists have been paying special attention to the role of leucine as a source of ATP (the main energy substrate of the body). The oxidation of leucine in the muscles gives even more ATP molecules than the same amount of glucose. And given that the oxidation of leucine and glucose goes along different paths, the athlete receives 2 powerful sources of ATP at once, that is, he restores his strength much faster.
Muscle protein synthesis
As mentioned above, BCAAs make up a third of all amino acids in muscle proteins, so they can be considered the main building material of muscles. Protein can be synthesized only if there are free amino acids, otherwise growth stops. At rest, to fill the need for amino acids, it is enough to take protein, which is gradually absorbed from the intestine and fully satisfies metabolic needs, however, during and immediately after training, the need for amino acids increases sharply, and the amino acid pool is depleted, so there is a need for large supplies of amino acids. Thus, by taking BCAA in the form of sports nutrition, an athlete creates favorable conditions for restoring the amino acid pool and building new muscle fibers immediately after training.
BCAAs as sources of glutamine
Glutamine plays an important role in muscle growth. Glutamine is contained in large quantities in muscles and other tissues, performs a regulatory role in the synthesis of all types of body protein, shifts the nitrogen balance to the anabolic side, increases the volume of muscle cells and increases the production of growth hormone.
The increased consumption of glutamine during exercise can be covered by BCAAs, which are able to be converted into it directly in the muscles.
Stimulation of insulin secretion, PI3K and protein synthesis
One of the pathways that accelerates protein synthesis (i.e., muscle growth) is the phosphatodyl-inositol-3-kinase pathway (PI3K). PI3K regulates glucose consumption and accelerates the transport of amino acids into cells. Insulin performs its anabolic effect precisely at the expense of PI3K.
BCAAs (leucine) are able to increase insulin secretion and directly activate PI3K, thus, anabolism is triggered even in the absence of insulin. The use of carbohydrates and BCAA amino acids after training leads to a synergistic increase in the level of insulin, activation of the consumption of nutrients by cells, acceleration of muscle growth.