I am not an expert on this, just going by what my vet told me, but here are some info sources:
Advice from John Houlton, Dipl. ECVS, Chairman of the World Veterinary Orthopaedic Congress 2010:
"As far as I know there is no published evidence on the relationship of exercise and developmental musculo-skeletal disease in dogs.
My advice to owners has always been that puppies should have normal exercise - including free running - but not an over-concentration on any one activity and always with the option to self regulate - i.e. they can always flop down and rest rather than being dragged across the Downs on a route march at the weekend.
What we do know for sure is that conditions like hip dysplasia involve the muscles, bones and joints and that puppies that have minimal exercise may be overweight and have poor muscular fitness meaning that they can put more strain on their joints and have poor muscular support for them.
My conclusion is that a lean fit puppy is in better shape to resist the clinical effects of HD and thus reasonable exercise is good.
Finally HD and elbow dysplasia are genetically driven diseases - if a dog has the genes to get the problem its going to get the problem all the other effects are marginal - they make a bit of difference but not as much as the genes."
Also:
Canine Hip Dysplasia Part II
Causative Factors of Canine Hip Dysplasia
Owners must separate fact from myth when examining theories on genetic, nutritional and environmental factors that influence CHD. By John C. Cargill, MA MBA, MS and Susan Thorpe-Vargas, MS
"While environmental effects, to include nutrition and exercise, may play a part in mitigating or delaying the onset of clinical signs and clinical symptoms hip dysplasia remains a genetically transmitted disease. Only by rigorous genetic selection will the incidence rate be reduced. In the meantime, it makes sense to have lean puppies that are exercised regularly and to avoid breeding any animals from litters that showed signs of hip dysplasia. It is probable that even normal exercise levels may increase the phenotypic expression of CHD of a genetically predisposed dog."
You can read this at
http://www.woodhavenlabs.com/chd2.htmlI took an interest in this after being chastised by a breeder for walking my 8 month old puppy at all. She said he shouldn't even be out of the garden until at least 12 months, so I asked my vet for advice. I think really it is just common sense -don't pound the pavements for hours but don't let your puppy get fat and unhealthy either.