I think like everything else - this can be taken to the extreme. I would worry about over-conditioning a dog, i.e.: excessive workouts that will long-term cause more harm than good. IPO is already hard on a dog, by adding more physical stressors the dog may be breaking down physically prematurely. The people in those videos may have some great results, but they may not be as concerned about keeping the dog healthy and hale into the senior years.
Talking to a Canadian mulit-national competitor/winner, WUSV multi-competitor about how he conditions his dogs for international level competition he mentioned two things: Weight pulling and swimming. For weight pulling, you'd be surprised, they had a special-made harness and the dog would work 15-20 minutes a day pulling a . . . (are you ready for this?) . . . 5 lb weight. Yes, FIVE pounds! He was amazed at how this developed the dog's muscle mass and strength, without taxing the system.
For swimming, he would take his dog out to a lake and swim her for 30 minutes a day (out in a boat, dog swam for 30 minutes no break) - of course, they worked up to that level slowly.
Bottom line is that these were low-impact exercises that did not put continous, extreme stress on the the joints, or force the dog to the edge of exhaustion. Again, long-term sustainability was the goal. Keep the dog healthy and active into her senior years.
Can you give some more details on the low-impact weight pull setup? How did he hitch all this up, what sort of harness, etc. Very interested in that.
GSDs- Mulder, Ridley, Vega
GSD on the half shell- Rigel