HOW YK11 WORKS, MECHANISM OF ACTION
YK11 has a similar chemical structure to the dihydrotestosterone (DHT) from which it is derived, and both hormones YK11 and DHT bind to androgen receptors (AR). However, unlike DHT, YK11 does not induce the physical interaction between the NTD/AF1 and LBD/AF2 (known as the N/C interaction), which is required for full transactivation of the AR. In other words said, YK11 activates AR only partially, without the N/C interaction. Such partial (limited) activation of androgen receptors increases the catabolic activity in the body. However, YK11 also induces the expression of Follistatin (FST), an autocrine glycoprotein that is a potent inhibitor of the effects of Myostatin, a protein that brakes muscle growth. Thus, the resulting potent anabolic effect of YK11 is thought to be primarily due to the induction of expression of Follistatin, which blocks effects of Myostatin. The resulting anabolic activity of YK11 in C2C12 myoblasts is more potent than the anabolic activity of DHT.
YK1 IS DIFFERENT FROM CLASSIC SARMS
YK11 differs fundamentally from other, “classic” SARMs (such as LGD-4033, Ostarine or RAD140) in multiple properties:
While common SARMs are non-steroidal selective androgen receptor modulators, and have a non-steroidal structure, the structure of YK11 has been derived from the structure of 5-α-dihydrotestosterone (DHT), so YK11 is a steroidal selective androgen receptor modulator (SARM).
Furthermore, common SARMs are full agonists of the androgen receptor (AR), YK is a partial agonist of AR. Full agonists bind to and activate a receptor with the maximum response that an agonist can elicit at the receptor. Partial agonists also bind to and activate a given receptor, but have only partial efficacy at the receptor relative to a full agonists. A partial agonist does not reach the maximal response capability of the system even at full receptor occupancy.
And third, YK11 is also unique in that it induces follistatin (FST) expression. Conventional SARMs are not known to induce follistatin.
Due to these differences, the mechanism of action of YK11 also considerable differs from the mechanism of action of conventional SARMs. Which means that also its possible side effects, risks or their extent may differ from common non-steroidal SARMs. Further extensive research is needed in this area as well.
YK11 HAS OSTEOGENIC ACTIVITY AND CAN HELP STRENGTHEN BONES
Like many androgens, steroids, and other SARMs, also YK11 has the ability to bind to androgen receptors in bone tissues and increase bone strength. A scientific study published in 2018 showed that the treatment of YK11 accelerated cell proliferation and mineralization in MC3T3-E1 mouse osteoblast cells. Further, YK11-treated cells increased osteoblast specific differentiation markers, such as osteoprotegerin and osteocalcin, compared to untreated cells. Elevated levels of activated PKB (protein kinase B) in cells suggest that YK11 activates the Akt / PKB signaling pathway through non-genomic AR signaling. Akt / PKB signaling pathway is a key regulator of androgen-mediated osteoblast differentiation.
YK11 AND BODYBUILDING
Thanks to its unique ability to induce Follistatin and significantly help build muscle mass, YK11 has also become a subject of interest for bodybuilders. However, YK11 is not an approved nutritional supplement or stimulant for athletes. It is an experimental substance, that has so far been scientifically studied very little. In addition, the possible side effects of YK11 have not yet been scientifically investigated (at all). This means that such experimental, unscientific use (abuse) of YK11 can be highly risky or dangerous. 
SCIENTIFICALLY INVESTIGATED POSSIBLE BENEFITS OF YK11
Significant and selective anabolic effect on muscles and bones (osteogenic acitivity)
Ability to induce Follistatin expression
Can help build muscle mass effectively
Can help strengthen bones
YK11 POSSIBLE SIDE-EFFECTS AND RISKS
Possible side effects of YK11 have not yet been scientifically investigated (at all). Theoretically, also the following side effects are not excluded:
Suppressed levels of natural Testosterone in the body (quite likely)
Increased risk of heart attack and stroke
Liver toxicity (due to the structure derived from DHT)
Can increase the progress of some cancer types (due to the increased expression of Follistatin)
The bodybuilding community on the Internet has experienced and reported with respect to YK11 some typical side effects, that occur with steroid use:
Mild testosterone suppression
Fatigue, low energy level
Aggression
Joint pain
Excessive hair loss
Mild acne