Waccamaw shared their interval weight pulling regimen with me back in 99, and ever since I incorporated that kind of weight pulling in the keep I sell, the people who have traditionally used the mill have *all* noticed a marked difference in performance in the animals they've applied it to. Like almost a night-and-day difference in many cases, which only makes sense, conceptually, when considering the fact that a fight involves struggle and the exertion of strength (not just "running "free" on a spinning belt).
The way Wac did it involved two people working the dog, one behind the dog adding/removing weights, and one in front of the dog baiting him with a flirt pole. If a person is working the dog solo, throwing a Kong Ball is a great idea to accomplish this, as well as to keep the work fun for the dog.
Jack