Free vs. Total Testosterone
Your total T can look fine on paper while the number that actually does anything is in the dirt.
Grounded in the research on free testosterone
Isn't total T the number?
No. Total testosterone counts every molecule in your blood, but most of it is handcuffed to proteins and can't do a thing. Roughly 44% is locked to SHBG, about 54% rides loosely on albumin, and only ~2% floats completely free. The receptors in your muscle, brain and libido circuitry only care about the testosterone that can actually reach them. Total is the headline. Free is the story.
So what's 'free' testosterone?
Free T is the tiny unbound fraction circulating with nothing gripping it, ready to walk into a cell and hit an androgen receptor. Add the albumin-bound chunk, which detaches easily, and you get 'bioavailable' testosterone, the portion that's functionally usable. The SHBG-bound half is the dead weight. SHBG grips hard and doesn't let go, so that testosterone is real, measurable, and useless to your tissues.