Teen Queen of Slalom

For American ski prodigy Mikaela Shiffrin, practice (and lots of sleep) makes perfect

As one of the youngest racers on the World Cup tour, 18-year-old Mikaela Shiffrin has an advantage over her older competitors: sleep. That's important, because in her specialty, the slalom, some of the races are run at night. "People waste energy in the morning, and they have none left at night," she says. Shiffrin spends those late-race days logging z's and then some. "I sleep a lot, as a teenager," she says, "and even as teenagers go too."

Maybe her opponents can't sleep because they know they face in Shiffrin the reigning world slalom champion and the first American to hold...