You probably noticed it on a staircase, or standing on one leg to pull on a shoe, or stepping off a kerb in the dark. Something felt less certain than it used to. Strength was fine. Breathing was fine. But the steadiness that used to be automatic had quietly become something you had to think about.
That shift happens earlier than most people expect, and it has a specific explanation. Balance is not a function of muscle. It is a function of information, and the system that gathers and processes that information starts changing in the fourth decade of life, well ahead of any meaningful loss in muscle mass or aerobic capacity.
