The original sled dogs were chosen for size, strength and stamina, but modern dogs are bred for speed and endurance Most sled dogs weigh around , but they can weigh as little as , and can exceed . Sled dogs have a very efficient gait, and "mushers strive for a well balanced dog team that matches all dogs for both size (approximately the same) and gait (the walking, trotting or running speeds of the dogs as well as the 'transition speed' where a dog will switch from one gait to another) so that the entire dog team moves in a similar fashion which increases overall team efficiency." They can run up to . Because of this, sled dogs have very tough, webbed feet with closely spaced toes. Their webbed feet act as snow shoes.