YK-11 is a steroidal SARM (19-Nor family) that’s meant to be a Myostatin inhibitor. Despite its interesting features, it’s never been tested on rats or primates and we have very little scientific information about it. Most of what we know is just speculation based on its effects on C2C12 cells. And since testing myostatin levels through bloodwork is hard and expensive, it’s really hard to see the results of our own experiments with YK11.
In any case, here you will find the most comprehensive YK11 guides on the web, all based on the latest academic data, and the analysis of mass anecdotal info.