Work ethic was scored on a three-tiered system based on the dog's willingness to run. The effort a dog put forth during a run was determined by the amount of tension a dog placed on their individual tug-line. The tug-line, indicated with yellow, is the line attaching the dog's harness into the main line connecting the dog team to the sled. Dogs demonstrating the strongest effort, defined by having a constant tug-line tension throughout the run, were designated as rank 1 (top line). Rank 2 (middle line) defined dogs that had intermittent tug-line tension throughout the run, but maintained the speed of the team. The poorest performers, rank 3 (bottom line), showed no tug-line tension during the run but were capable of the speed and mileage. Dogs were not penalized due to the affects of injury.
Huson et al. BMC Genetics 2010 11:71 doi:10.1186/1471-2156-11-71