Specific muscle-building exercises can make dogs stronger. According to Active Dogs, weight vests, weight-pulling and carrying weighted objects help strengthen the muscles of a dog.

A weight vest is worn around the dog's torso while the dog walks or trots during a formal exercise period. Weight vests strengthen all of the dog's muscles, but according to the experts at Dog Tread, even very fit dogs shouldn't carry more than 10 percent of their bodyweight in vests or backpacks to prevent injuries. Unfit dogs should start out carrying very light weights and only gradually work up to the 10 percent level.

Weight-pulling is both a competitive dog sport and an excellent way to develop a dog's fitness, according to the International Weight-Pull Association. Weight-pulling requires the purchase of a special harness for the dog. Many people use old tires or barbell weight-plates to exercise their dogs. Others have the dog pull people in a sled or cart. As with carrying weight, when the dog pulls weight, only light weights should be used at first. As the dog gets stronger, it can pull heavier loads, at least for short distances. For example, Whole Dog Journal reports that a 40-pound dog is capable of pulling almost 4,000 pounds.

Weighted retrieve objects can also be used to develop the dog's neck and jaw muscles. Active Dogs sells a weighted ball that weighs 6 to 12 pounds with a handle that allows the dog to fetch it.