Had to pitch in on this one.
Running dogs too much, too young is not advisable. Background and disclaimer: I own, show (conformation, obedience and field trials) and run with Rhodesian Ridgebacks, arguably one of the greatest endurance breeds. My veterinarian breeds and races Huskies, arguably the greatest endurance breed. He and his father have a combined 60 years of experience there. None of us are obese and neither are any of our dogs.
The most common consequence of running a dog too much too young is hip displasia and arthritis later in life. If you get it wrong, your dog - about 8 TO 10 YEARS from now - will need multiple ~$5000 surgeries, continuous Rimadyl treatment and will be unable to walk or run without significant pain. And it will be your fault.
Just a year or so of patience and restraint, however, will give you a running partner for five to ten years who will enjoy a happy old age. If you can't show that level of patience you probably consider not owning a dog. There is no instant gratification in dog ownership...
So how little? For most Lab/Rhodesian sized dogs, no more than10 minutes continuous running from 6-9 months, no more than 20 minutes from 9-12 months and no more than 30 or 40 minutes from 12-18 months. Then you are good to go. One of my Rhodesians then easily built up to an hour and 45 on hilly trails at about 7:30 pace before her second birthday. Until that time, I'm sorry, but it's about the dog, not about your workout.
But puppies run like crazy the whole time, I hear you say. True, but they stop frequently, which they generally can't do on a run.
Finally, DO attend several rounds of puppy school with your new buddy. If your dog does not show good recall, not jump up at strangers, not run at heel when commanded (off leash) etc., guess who's to blame. (Hint: it's not the dog...)
Sorry to preach and sound badass about this, but running a puppy for an hour is akin to making your 10 year old human child run marathons. And not doing the obedience thing is akin to not sending them to high school!
AD