Balance training conditions the proprioceptive system. The sensors and reflexes that maintain upright posture against perturbation.
Mechanism: Improves vestibular, visual, and somatosensory integration. The neural pathways for balance are use-dependent and decline rapidly after 50 if untrained.
Use case: Single-leg stands, unstable surfaces, tandem walking, eyes-closed work. 5-10 minutes 3x/week. The strongest mortality lever in over-65 populations.
Caveats: Falls are the #1 cause of injury death over age 65. Balance is trainable at any age. Test with single-leg stand: 30s is good, 60s is excellent.