At some point in the past seven months you signed up for the American Birkebeiner. Maybe you’ve done it before, maybe you haven’t. Either way, you’re now committed to skiing the American Birkebeiner, excited to experience “Birkie Fever,” whether for the first time or the 20th time. No matter your level of skiing or your goals for the Birkie, tackling a 50-kilometer ski race is no small feat. Realistically, for many people who participate, training...