Iditarod mushers are discovering on the trail what scientists have suggested in the laboratory -- that sled dogs are capable of greater feats of endurance than previously thought.
Lance Mackey of Fairbanks first expanded the perception of what was possible with his back-to-back victories in the Yukon Quest International Sled Dog Race and the Iditarod Trail Sled Dog Race the past two years.
Then the teams of Jeff King of Denali Park and Mitch Seavey of Sterling buttressed Mackey, following up strong Iditarod runs with even stronger runs 13 days later in the 408-mile All-Alaska Sweepstakes.
King and Seavey, Iditarod champions both, as well as perennial contender Zack Steer of Sheep Mountain believe Mackey discovered something important -- the longer dogs run, the better they get.
"Who would have thought that you could warm up for a 1,000-mile race by running a 1,000-mile race?" Steer said. "Mushers never thought that could be done; the demands would be too much. Lance has thrown all that into the wind. A lot of mushers are scratching their heads. Maybe the dogs actually get better."
All three mushers said their teams are able to run longer stretches toward the end of the race -- and with less rest -- than at the beginning, although their speed slows.
"At the end of the race, they can do 10-, 12-, 14-hour runs," Steer said. "You'd never do that at the beginning."
In mushing lingo, the team becomes "trail-hardened."
Steer tempered that by saying teams do tire and are not "fatigue-proof." Nonetheless, the dogs seem to get into a zone that allows them to run for long stretches.
"Their aerobic endurance level seems to improve," he said. "It's hard to describe. They're not physiologically stronger, but they have a reserve they can tap."
What convinced King was his runner-up finish in the Sweepstakes, which took place outside of Nome. Using his Iditarod team, King finished second, just 10 minutes behind Seavey, who also used his Iditarod dogs.
King was stunned how well his team performed.
"They did things I did not believe they could do," he said.
The team ran so well that King, a training innovator who has his dogs swim during the summer to boost their endurance, is rethinking some of his philosophies.
"I'm excited, but I'm also baffled," he said. "We just turned a page. It's like you think you know how big the universe is, and then you get a better telescope and 'Oh my God, I can see the edge!' Well, I don't see the edge. I'm dumbfounded."
Both King and Steer have worked with Dr. Michael Davis, an associate professor of veterinary physiology at Oklahoma State University who has studied Iditarod sled dogs. King said his dogs ran on a special treadmill to test VO2 max, a measure of how much oxygen the body uses per minute. Fit athletes such as marathoners and high-altitude mountaineers typically have a very high VO2 max.
Two years ago, Steer worked with Davis to test for gastric ulcers in the dogs during the Copper Basin 300 race near Glennallen. Davis believes sled dogs somehow change their metabolism during a race, allowing them to burn calories at a high rate without depleting fat and glycogen stores.
Stuart Nelson, the Iditarod's chief veterinarian, termed what happens as "a metabolic adaptation" to the increasing demands of the race.
"A change occurs in their system, and they get stronger as they go down the trail," he said.
Diet is also important, Nelson said. A sled dog may burn 10,000 calories a day during a long-distance race. To compensate, mushers increase the level of fat in dogs' diets as the race progresses.
Seavey cautioned that it's not clear if the benefits of such high mileage outweigh the risks. But he echoed King in saying that his team was "incredibly tough" during All-Alaska Sweepstakes.
"And they were happy about it. It was really no big deal," Seavey said. "That was the neat thing. They didn't seem to think it was difficult.
"That's one of the things that keeps us fascinated with this sport," Seavey added. "I've been in competitive athletics, so I'm somewhat familiar with human abilities and endurance, and man alive, these dogs make us look like total wimps.
"If people who are critics of long-distance mushing had any idea how capable these dogs are, they might rethink their positions. There's a level of ability and endurance that we can't quite comprehend."