I’m watching a show on Discovery Channel about the running of the Iditarod sled-dog race. It’s one of the longest races, about 1800 km. It recalls a famous delivery of diptheria vaccine to Nome, Alaska, through a blizzard in the ear;y 1900s. There are racers (human and canine), fans, and volunteers. Most of the racers rest at one of the checkpoints; others push on to find a quiet place. It’s important for the dogs to rest. Some winners do 51% racing, 49% running. About four hours of rest seems to be enough. It’s very important for the dogs to eat: they can burn off 9,000 kilocalories a day.