Bone mineral density (BMD) measures the mineral content per unit volume of bone, typically via DEXA scan. T-scores compare to a young adult reference.
Mechanism: Bone remodels in response to mechanical load. Without loading (resistance training, impact), osteoblast activity declines and osteoclast activity dominates. Net loss. Women lose density rapidly post-menopause due to estrogen drop.
Use case: Resistance training (especially heavy compound lifts), impact work (jumping, running), adequate protein and calcium, vitamin D, K2. DEXA scan every 2-3 years after 50.
Caveats: Osteopenia and osteoporosis are preventable but not always reversible. Start training before you need to.