Exersise for Labrador Retrievers

Question
I am interested in knowing your recommendation for exercising Labrador retrievers at various ages.  I am asked quite often by people about how much is too much. Puppies playing do a lot of running about. I know running and jumping in excess is not good before two years of age, but in what context.  Can a one and a half year old go for a 30 minute jog ( 5 km ) twice a week and it not cause problems?

Answer
I don't know that there is any good information on how much is too much.  30 minutes of running on a paved surface does sound like too much for a 1 1/2 year old.  But that is just my judgment with little to back it up.  Many people give out strong opinions with little or nothing to back them.  I won't do that.  You might also have an X-Ray.  Many dogs with marginal hips show little symptoms at that age.  Too much running could bring on problems at an earlier age.  All the service dogs schools X-Ray all their dogs before training to avoid the expense of training an asymptomatic dog that won't be able to work very long.  

I can say he would be less likely to have problems if he is lean.  Your dog definitely should be narrower at the waist than the hips and chest. You should be able to easily feel the ribs, but not see them. Each dog is different. Standard recommendations are a good place to start, but each dog must have its food and exercise adjusted to its individual needs. Here is a link to a good illustrated guide, http://www.longliveyourdog.com/twoplus/RateYourDog.aspx