See Spot pull!
Over the years, many dog breeds have been used for their ability to haul people and their goods. From the Rottweilers that pulled the butcher's cart to market 200 years ago in Germany to the Siberian huskies that worked in teams pulling sleds and the Chukchi mushers that drove them. Dogs are no strangers to the pulling business.
Weight pulling is a sport that taps into this natural instinct. It's great exercise for the dog and its a terrific way to grow a stronger bond between you and your dog.