I don't run with Kyleigh (simply because I don't run), but my friend and I walk with the dogs (both are now 17 months old), and they have been best buds since pups.
We walk THEY run, and run and run and run. We take them tons of places where they are perfectly safe off leash, and let them be dogs - playing, running, wrestling, etc.
I posted in one thread that Ky and her friend once played for 4 hours. We wanted to see just how long it would really take to tire them out. (She was about 5 or 6 months old at the time.)
Now, I'm not saying to run your dog for 4 hours ... that would be cruel. But a puppy / dog playing with another dog, can certainly play / run longer than 20 minutes. They control themselves (at least our two do!) When they are tired, they take a break, and when they are rested they go back again.
I agree with Elaine, and others, who have said, sure, run them, just watch your dog carefully. When they are playing with another dog, they simply stop playing when they are tired. When you are running with them, they might not be as inclined to stop as they WANT to follow you!
If I was to start training to run (for myself), Kyleigh would leave me in the dust!!! I'm a great walker, but certainly no runner.
I think it's a great idea for BOTH of you - you to get in shape / keep in shape, and great for your dog to build stamina!
Marionís Zoo-Kyleigh, Raylan-cat, Echo-TAG,