Those who run long are not freaks of nature. We are not a handful of chosen ones blessed with indefatigable muscle and indestructible cartilage. Nor do we have indomitable willpower that others lack. If anything sets us apart it is a kind of sensitivity. We can hear a faint chord vibrating on old and brittle strings. It begins to resonate through us when we rise predawn for a morning run. The sound builds the longer we stay at it. On a long run through the mountains our attention becomes focused, in tune, automatic. Each footfall and each breath synchronized with a primal tune. Ours is a re-creation of once necessary dispositions.