Packed in a huddle of fast moving bodies, I only noticed the crack in the ice when I hit it at full speed. In a flash, I went from hunched concentration to a full-out sprawl. Stunned, as soon as I picked myself up from the surface of the frozen lake, I saw my predicament: my right skate’s blade was hanging from my boot, barely connected—and that’s how my ordeal began. On that steely, sub-zero day in January,...