labs are awesome dogs. very active dogs. as far as running a marathon, I dont know. from your thread title, I thought you meant like having a dog run in a park. but a marathon? get a grey hound or somehting...
I've got a Golden Retreiver and he's fine to go running with for about 2 miles. I don't know how much further he'd make it after that. He's usually breathing harder than I am.
I guess any dog could keep up with you, but think about that you shouldn't be running/biking with the dog until it's at least 18 months and have been x-rayed (sp) on the hips...
pitbull,huskies,airedales, etc etc any dog that is not over 100 and not to blocky wold be a good running partner. I ran with my 95lb american bulldog but he was just to stocky and to low to the grond to last
I run every other day with my border collie. Dogs are the best running partners... they love it love it love it. I used to run with my dog's sister when she was a pup. She and I started running together when she was just 12 weeks old. I couldn't keep up with her then.
Just remember, though, a dog has to work up to being an athlete just like you do. Start easy... and watch their gait and paws. If they catch a thorn you need to spot it. (I once had to carry my dog for two miles down a mountain trail after she ran through a clump of briars.)
just don't be cruel. you need to act like a spotter when you see them falter a little relax the pace, dogs have a hard time running over 2 miles cause they are running on all four and are not trained to do that much, shit they sleep all day at home....