You guys are naive if you think a dog before 18 months doesn't sprint at least a mile while playing fetch. Or jog at least a couple miles on a hike. Why don't people stop doing those activities?
It's the high impact stuff that has the possibility to alter hip growth. Stuff like a dog constantly jumping up for a ball and landing on its hind legs.
It's amazing people can throw a ball over and over for a dog but jogging with a dog (which is a much slower rate of speed than a dog sprinting after a ball) is somehow a big no no?