This site has some great info on how not to over exercise your pup not to mention lots of other great info. Please anyone getting a new pup please check it out.
Are you helping or harming your puppy when you take him for a walk? The right kind of exercise will promote health, intelligence, and calmness in your puppy. The wrong kind of exercise may create behavioral and physical problems that can last a lifetime. Do you know the difference?
Source: APPROPRIATE EXERCISE