YK-11 (YK-11) is a synthetic steroidal selective androgen receptor modulator (SARM) that has attracted significant research interest due to its unique dual mechanism of action. Unlike traditional SARMs, YK-11 functions as a partial androgen receptor agonist while also increasing follistatin expression, a protein associated with the regulation of myostatin activity. Researchers commonly investigate YK-11 for its potential effects on muscle cell differentiation, lean tissue development, and anabolic signaling pathways. Its distinctive pharmacology and potential influence on muscle-growth regulatory mechanisms have made it a widely discussed compound in performance and muscle biology research, though human clinical data remains limited.