Dog sledding is an old form of transport used to cross wintry terrain. The set-up consists of a musher (driver) and a formation of dogs that pull the sled. The sleds are specially designed and come in different varieties; some look like carts with wheels, and some are adapted scooters, which can be used on land. The musher stands behind the dogs. The heavier the cargo, the more dogs you need: instead of horsepower, think dogpower. The dogs each have a role within the team; those closest to the sled are called 'the wheels', they provide the acceleration. Those next furthest from the musher have different roles depending on the size of the team..