The majority of BCAAS have L-Leucine, L-Isoleucine, and L-Valine.
L-Leucine is the primary amino acid that produces protein synthesis. It is a prerequisite for producing muscle growth.
Leucine's primary action is producing the effect of Mammalian target of rapamycin (mTOR).
These stimulator activities result in protein synthesis building. mTOR activation is essential for skeletal tissue growth.
Anthony JC, et al. Leucine stimulates translation initiation in skeletal muscle of postabsorptive rats via a rapamycin-sensitive pathway. J Nutr (2000)
Drummond MJ, et al. Rapamycin administration in humans blocks the contraction-induced increase in skeletal muscle protein synthesis. J Physiol (2009)