Ruka, Finland looked quintessentially Nordic at the start of the 10-kilometer freestyle pursuit. December at 66 degrees north: temperatures in the low teens (F), flat Northern light, frosted pines looking as though they were spray-coated with foam. Athletes warmed up in puffy jackets with mittens, neck warmers, and taped faces while crowds huddled with cups of soup. First out of the start and racing in a balaclava and mittens, Norway’s Theresa Johaug attacked the course...