YK-11 may be the most powerful muscle building compound on the entire planet, perhaps this is a arrogant claim, but I will deeply support it, YK-11 is the strongest SARM for building muscle mass. While other SARMs work by targeting androgen receptors (ARs) in the body, YK-11 is actually an anti-myostatin inhibitor.that has gained attention in the fitness and bodybuilding community. It is known for its potential anabolic properties, which means it may help in promoting muscle growth and strength.