Amino acids are the building blocks of proteins, but they also act as stimulators of biochemical pathways that synthesize proteins. Likewise, optimal muscle blood flow is considered important for maximizing muscle protein synthesis in weight-trained athletes. Arginine is an important signaling chemical involved in muscle protein synthesis and promotes muscle blood flow by increasing the production of nitric oxide (important controller of blood flow).
Researchers from the U.S. Department of Agriculture found that arginine promotes muscle protein synthesis by stimulating the mTOR pathway rather than via nitric oxide production. This study showed that influencing biochemical pathways that promote protein synthesis is more important than stimulating muscle blood flow for muscle growth. (American Journal of Physiology-Endocrinology Metabolism, 299: 899-909)