What kind of dog?
My dog's lucky to make a mile in the summer heat.
56% Great Dane, 19% German Shepherd, 8% Pit Bull, 6% Boxer. The remainder combining 7 different breeds, including Rottweiler, Golden Retriever, and American Eskimo Dog) in various percentages, none more than 2%.
He looks like a less jowly Great Dane with very dark coloring, about 100 pounds, at the moment. He's more muscular looking than the Great Danes I've seen, and smaller than the really big Great Danes. His first 1-2 years were spent almost entirely outdoors in the mountains, free to roam wherever, chasing or fighting with other animals all day long. This is a very, very fit dog. He's totally ripped, in part due to being underfed where he was.
The heat and humidity
has slowed him up some, and shortened the walks a bit. But on all but the most humid days, he's still doing between 7-9 miles per day with me, and up to another ~10 miles with my son.