Via the Atlantic, "Is It Safe to Exercise With Your Dog?"
This article made me feel a little guilty. I've had to learn a few of these lessons the hard way:
1) I definitely needed to ease my dogs into running! I'm a serious runner, and I started out taking them for maybe a half mile at a time (run a half-mile, walk back), which allowed us to work up to some longer distances, but...
2) Older dogs don't recover as well as younger dogs. I tried the same thing with my dogs a couple of months ago (two to three years after the height of their running prowess) and found that I had to cut the distance and pace back even further- they're both more comfortable with a brisk walk these days.
3) Body type makes a huge difference! My dogs are both herding mixes. The boy is about 40 pounds, the girl is about 50 pounds, but there's no way you could tell that she weighs 25% more just looking at them. You know when you absolutely CAN tell? About 3/4 of a mile into a run, when she starts to get tired and he's just getting started. She's a lot stockier and heavier than he is, and not really as well-suited to the distance running pursuit.