The Free Hormonal Index refers to the fraction of a hormone that is unbound to carrier proteins and thus available to bind receptors and exert biological effects. For testosterone, only 1–2% is typically "free"; the rest is bound to SHBG or albumin.
Why It Matters
- •Bioavailability — free hormone determines tissue-level activity
- •Total vs. free — total testosterone can be normal while free is low (e.g., high SHBG)
- •Performance — cognitive and physical performance correlate with free hormone availability
In ONDA Life
The CHM article covers performance window optimization based on free hormone levels.