Branched Chain Amino Acids (BCAAs) are a group of three essential amino acids: leucine, isoleucine and valine, which are characterized by their branched chemical structure. They are called “essential” because the human body cannot synthesize them and must be obtained exclusively through diet or supplementation. BCAAs represent approximately 35% of the essential amino acids in muscle tissue and play a central role in muscle metabolism. At a biochemical level, BCAAs are differentiated from other amino acids as they are largely metabolized directly in skeletal muscle and not in the liver. Leucine is the master anabolic regulator, as it directly activates the mTOR pathway, leading to stimulation of muscle protein synthesis. Isoleucine is involved in the regulation of glucose and its uptake by muscle cells, while valine contributes to maintaining energy balance and reducing central fatigue. One of the most important physiological roles of BCAAs is their anti-catabolic effect. During intense or prolonged exercise, BCAA levels in the blood decrease, which can lead to increased muscle proteolysis. Their supplemental administration limits muscle protein breakdown and contributes to maintaining a positive nitrogen balance. At the same time, they can be used as an immediate energy substrate in conditions of energy deficiency. From an ergophysiological point of view, BCAAs have been associated with a reduction in muscle fatigue and delayed onset muscle soreness (DOMS), as well as with faster recovery after training. This mechanism is partly related to the competitive action of BCAAs against tryptophan in the brain, leading to reduced serotonin production and, by extension, a reduced sense of fatigue. Overall, branched-chain amino acids are a scientifically proven ergogenic supplement, with the main benefits of supporting muscle protein synthesis, reducing muscle catabolism and improving recovery. Their use is particularly widespread in strength and endurance athletes, as well as in periods of caloric deficit, where the protection of muscle mass is of primary importance.