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California Runner

There's nowhere to go but up for a runner following a railroad track toward California mountains. Although doctors recommend regular exercise to maintain a healthy heart, long-term athletic training comes with risks. Swimmers, cyclists, rowers, and distance runners are among those in danger of developing "athlete's heart," or hypertrophic cardiomyopathy, an abnormal thickening in the walls of the heart that can bring about sudden death.

Photograph by Joy Tessman