As I understand it, forced on-lead walking, where the dog can't stop, start, meander and choose the pace is generally a bad idea.
Also, too much free running with other dogs and repeatedly ball/frisbee chasing, where the dog get's hyped up and stops listening to it's own body telling it to slow down and rest, are similarly bad.
Obesity is now being considered to be one of the major factors in elbow/hip problems, but it still holds true that repeated or excessive pounding on young joints is also a bad idea, particularly in larger/taller/heavier breeds, especially as in pet homes it's usually confined to short, frenetic periods as opposed to dogs that have been developing fitness from birth - as in the study cited on that thread.
Working dogs and those that remain with the breeder tend to have lots of free-play opportunities in paddocks and runs. As this is the norm - compared to shorter, defined, walks in pet homes, the pups don't get hyper and charge around like lunatics, but do romp and play, steadily building muscle and fitness, which supports the joints and encourages healthy symmetrical skeletal development.
That's how I understand it anyway.