Institute of Canine Biology ,,, Exercise is good and bad
Exercise strengthens the muscles of the legs and pelvis, and this will increase the stability of the hip joint. But all exercise is not created equal.
Puppies raised on slippery surfaces or with access to stairs when they are less than 3 months old have a higher risk of hip dysplasia,while those who are allowed off-lead exercise on soft, uneven ground (such as in a park) have a lower risk (Krontveit et al 2012). Dogs born in summer have a lower risk of hip dysplasia, presumably because they have more opportunity for exercise outdoors (Ktontveit et al 2012). On the other hand, dogs from 12-24 months old that regularly chase a ball or stick thrown by the owner have an higher risk of developing dysplastic hips (Sallander et al 2006).
The most critical period for proper growth and development of the hip in dogs is from birth to 8 weeks old, so the type of exercise the puppies are exposed to is most important during this time.
here's a good article https://www.puppyculture.com/appropriate-exercise.html
"for dogs under 1 year, I discourage any kind of "forced" exercise -- fetching, jogging, biking, etc. basically anything that is prompted by the owner and wherever the dog might do more than it should or would be including to do due to social facilitation by the owner.I think long line walks or off leash exercise over solid footing is ideal.
I've done this for decades with my dogs starting even at 3-4 months of age and never had orthopedic issues from it."
Lore I. Haug, DVM, MS, DACVB, CABC
President, American College of Veterinary Behaviorists