Re: How much exercise does a 4 month old need?
I ran just shy of three miles with Maddie, age 4.5 months, on Sunday. She was off leash and probably ran 5 miles given her diversions. Now I was not running fast at all (~13 minute/mile) but we were running on trails through the woods with some up and down topology. The pace included some walking/stopped time when we met another dog, etc. See graph.
By the way, she did a great job of disengaging from whatever she was pursuing and catching back up to me (and passing me) whenever I tooted the whistle I carried. The only thing that distracted her enough to challenge her to come was another dog that wanted to play. She usually did eventually come though.
I ran with her like this only after I realized she had a lot more capacity for running than I first imagined she might. On several walks through same trails before with friends and adult dogs, I'm guessing the dogs ran 3 to 4 times further than we walked, most at full speed.
Another time last week, on flat open ground, I ran right at a mile with her off leash at a 7 minute pace and she spent the whole time well in front of me looking back to see when I would catch up.
Of course, in any of these cases, I would have stopped had I thought she was over exerting. As the runs took place in the morning, I watched her the rest of the day, and she had her normal amounts of energy to play with kids, other dogs, etc. for the remainder of the day. She also gets very excited when I pull out my running shoes.
I guess I am saying for most of us average runners/exercisers, you probably have little risk of over doing it if they are off leash. If you are a marathoner stringing together a bunch of 5 minute miles, you might take it easy on your puppy.