IMO, the whole idea of "free conditioning" is counter-intuitive to what a dog actually does in a fight.

Resistance training, with periodic breaks, and periodic all-out efforts, is more in line with the reality of what dogs are actually doing in a match.

A fight is NOT just "pure cardio," with zero resistance; in fact a fight is quite the opposite.

There is another force of equal weight resisting your dog's efforts (and requiring your dog to put up a resistance to), for which muscular conditioning is absolutely needed.

Jack