OSLO, Norway — Here’s something dizzying: six times around an 8.3-kilometer course with a total vertical gain of just over two thousand meters. In non-metric terms, all 47 finishers on Saturday’s Holmenkollen 50 k classic race accumulated roughly 6,574 feet of climbing. On the sharp end of the race for most of those kilometers were Norway’s Martin Johnsrud Sundby and Finland’s Iivo Niskanen. They were the animators for the hordes of Norwegians lining the course...