swiming really got my dogs front legs jacked. she would swim 4 hours straight without stopping. the only mistake i made was i dint know how much more i should be feeding her.she never got skinny but i dont think she got as big as she could have. something i never did but i think would have been a good idea is put a walking harness on your dog tieing a rope to the harness and baiting the dog by throwing sticks over its head. my girl would kick her swiming into high gear when she was chasing a stick. by making them push them self by swiming as fas as they can you build larger stronger muscle.