Essential Amino Acids (EAA) are a group of amino acids that are absolutely necessary for the normal functioning of the human body, but cannot be synthesized endogenously and therefore must be ingested exclusively through diet or supplements. The EAA include nine amino acids: leucine, isoleucine, valine, lysine, methionine, phenylalanine, threonine, tryptophan and histidine. They form the basis for the synthesis of all proteins in the body and are critical for the maintenance of muscle mass and metabolism. At the biochemical level, essential amino acids function as both building blocks and regulatory molecules. Leucine in particular acts as a potent activator of the mTOR anabolic pathway, which is the central mechanism for stimulating muscle protein synthesis. Unlike individual BCAAs, EAAs provide all the necessary substrates for the completion of protein synthesis, making the process metabolically complete and efficient. The presence of all essential amino acids in plasma is a prerequisite for positive nitrogen balance. Deficiencies of even one EAA can limit or inhibit muscle protein synthesis, regardless of the adequacy of the others. For this reason, EAA supplements are considered particularly effective in situations where total protein intake is limited, such as in caloric deficit, fasting or intense training stress. From an ergophysiological perspective, EAA supplementation has been associated with increased muscle protein synthesis, improved recovery after exercise and reduced muscle catabolism. Furthermore, due to their rapid absorption and low caloric value, they can be consumed before, during or after training, without burdening the digestive system. Overall, essential amino acids constitute a scientifically proven and functional supplement, with high metabolic value. Their use is particularly widespread among athletes, people following hypocaloric diets, as well as populations with increased needs for maintaining lean muscle mass, offering effective support for protein synthesis and overall muscle health.