As you know, your body naturally produces testosterone. Your body also produces a globular protein called sex hormone binding globulin (SHBG). SHBG can bind to your testosterone, creating what is called "bound testosterone." Bound testosterone cannot bind to the androgen receptors on your muscles and turn on the growth switch. So, testosterone that is "free" from being bound to SHBG is more ideal.
Think of SHBG as gum. Your testosterone is the key. And the key holes are the androgen receptors on your muscles that open the door to muscle growth. Testosterone is FREE to open doors if there is no SHBG "gum" stuck to the key (testosterone), and the more FREE testosterone you have, the more doors you can open to turn on the muscle growth switch.
