Question: Our puppy (8 months old, Husky/Shepherd mix) is getting to be good enough on the leash that I can take him for a nice run. I live near a park with a 5K loop road, which I used to run regularly. 

When I first started taking him out around the loop road, he'd jump at me and bite and try to get me to play right away, or at least at fairly arbitrary intervals. I got a good lesson in dominant walking, and a better slip lead that actually loosens again after I tug it so I can keep it high on his neck, give it a quick tug and re-orient him to following me and we can keep going. That had a huge impact--he's way, way more manageable. My pace is pretty slow, he seems to handle it very comfortably, and we stop for water. 

But since the walking lesson I've noticed that about 2/3 to 3/4 of the way through, he still gets really unmanageable. He tries to jump on me and bite playfully, but he forgets his bite inhibition entirely. The other day he did this really manic digging for a few minutes. Just scraping at the soil with dirt flying and shaking his head and jumping around. In general, it seems like he just gets manic and bonkers, jumping around and barking at me.

It occurred to me (this might be obvious to everyone else?) that 5K might just be too long for him to run. Do I need to find a shorter route, or is there something else going on?

P.S. There's a mention of overtiredness at [What can I do if my puppy is hyperactive?](https://pets.stackexchange.com/questions/141/what-can-i-do-if-my-puppy-is-hyperactive?lq=1) which seems to suggest that's exactly what is going on. But I'd love to know more about how to tell when a young dog is getting overtired.

Answer: 
I would definitely ask his vet how much he thinks is too much for the dog's age and physical state. 
Then I suggest you see how long does he sleep after he arrives home (if you are not running just before going to bed). Dogs can easily get overexcited and push themselves too hard just to please their owners. What gives me the best idea of how much exercise my dog needs is not how he behaves while outside (he's a Boston Terrier 10 months old, could stay out running, jumping and playing with other dogs forever) but how he behaves once he has arrived. If he sleeps for two hours straight it was a good workout, if he sleeps for four it was definitely too much, anything less than two hours of straight sleep and we have to go out again later in the day if we want a calm dog at night. Of course those numbers might not apply to your dog, but I think you'll find this method to give you a good idea of how much exercise he needs to be happy.
I have a Siberian Husky that is not much older than your dog. As I take him for a jog/walk, he will do the same thing sometimes such as bite the leash or jump around. 

It could very well be the case that your dog is bored of walking and wants to run or at least go faster. This makes sense for a Husky Shepherd. They have lots of energy and your goal should be to help them exert it.