At 5,700 feet above sea level, the Kandilli Nordic Ski Center in Erzurum, Turkey has presented World Junior competitors with some of the most painful racing they’ve ever experienced. As became clear from the depth of Russia’s dominant results—a team that took a two-week altitude camp in Bulgaria prior this week’s racing—acclimation to altitude has played a major role in the outcome of World Juniors and U23s, for all levels of athletes. In more than...