We have talked a lot about the benefits of BCAAs. I mentioned that Leucine is the most important of the BCAAs. When it comes to signaling muscle building (protein synthesis), Leucine is king. It has been shown to increase protein synthesis by up to 145%. In terms of direct effect it may be the single most important amino acid for hypertrophy.
Leucine is one of the branched chain amino acids (BCAA). Exercise leads to the oxidation of BCAA’s as a primary source of fuel as well as signaling pathways for recovery. BCAA’s are unique in that they can lead to increased insulin and cortisol depending on the situation. Leucine is the most important of the 3 BCAAs for signaling muscle growth. Leucine leads to the signaling of a pathway called mTOR, which is the same signaling pathway that is activated by growth factors like IGF-I. In fact Leucine acts in a more direct way on the mTOR pathway than growth factors because it does not require as many intermediate steps.