I don't know much about Iditarod, but those dogs look scrawny and don't look like Huskies. They look like mixed breeds you would see that are up for adoption at the dog pound. Not that they can't do the work, though.
Some years ago, we went to a farm to pick out a corgi puppy for our family. The family's son was raising corgis to help pay for his college education. When we arrived, sitting in front of the barn were two Border Collies. They looked lean, I suppose that could be mistaken for scrawny, and they were alert. You could tell they were working dogs.
The farm was really well maintained. She took us out to another shed where there was another batch of pups that looked recently whelped, and the whelping bed that the female and pups were in was very clean, as was the rest of the farm. These people took care of their animals and their buildings and land.
So, it may just be that a dog who is a working dog, and gets a lot of exercise, looks scrawny to our eye compared with house pets that we usually see. But, I think they are just lean.