Skeletal muscle protein turnover is modulated by intracellular signaling pathways involved in protein synthesis, degradation, and inflammation. The proinflammatory status of muscle cells, observed in pathological conditions such as cancer, aging, and sepsis, can directly modulate protein translation initiation and muscle proteolysis, contributing to negative protein turnover. In this context, branched-chain amino acids (BCAAs), especially leucine, have been described as a strong nutritional stimulus able to enhance protein translation initiation and attenuate proteolysis. Furthermore, under inflammatory conditions, BCAA can be transaminated to glutamate in order to increase glutamine synthesis, which is a substrate highly consumed by inflammatory cells such as macrophages. The present paper describes the role of inflammation on muscle remodeling and the possible metabolic and cellular effects of BCAA supplementation in the modulation of inflammatory status of skeletal muscle and the consequences on protein synthesis and degradation.Fascinating paper if you're into this sort of thing - and I am. Inflammation appears to be the main cause of the so-called "resistance to anabolism" of aging, which as I mentioned recently is characterized by increased inflammation. BCAAs, especially leucine, work to increase muscle synthesis and prevent muscle breakdown, and they do this possibly by attenuating inflammation. This opens the way for treatment of some diseases of aging characterized by inflammation, most especially sarcopenia.
And of course, BCAAs are good for weightlifters too.