Last summer we ran Marco 3-4 times a week (about 1-2 miles) in addition to a daily walk. I want him to get a bit more exercise and have switched to biking. We are going a bit faster (still a trot) for about 2 miles with intermittent sprints. I noticed that his hind quarters nearly double in size after the run and I never noticed it when we ran on foot.
I do a bit of lifting and was curious if this "pump" was the same thing I experience in the gym (perfectly natural and shows a good workout) or if this is a sign that we're going to hard. Marco is almost 2 years old (80lb) Am Staff. He didn't show any sort of pain. He favored one of his hind legs very briefly the next day going down the stairs (5 flights) which I attributed to being a bit sore from the run. Besides being totally pooped out he is as happy as can be.
TL,DR - Ran dog hard, hind quarters swelled up like a balloon (double in size)