AR
AR androgen receptor — the molecular target that 11 compounds in the wiki act on.
In one line: The docking station inside muscle cells that testosterone plugs into to switch on muscle-building.
The androgen receptor (AR) is a protein that sits inside your cells, waiting. When testosterone (or a steroid, or a SARM) floats in, it plugs into this receptor like a key into a lock. The locked pair then travels to the cell's DNA and switches on the genes that build muscle, make red blood cells, and strengthen bone.
This one receptor is the single most important target in the whole "build muscle" world. Every anabolic steroid, every SARM, and testosterone therapy itself all work by plugging into it. They differ only in how tightly they grip it and which tissues they favour.
The catch: the same receptor exists in your prostate, skin, and scalp — so flooding it (as steroids do) causes side effects far beyond muscle. SARMs were invented to try to hit the receptor mainly in muscle and bone while sparing the rest, though none is perfectly selective.