The car/bike does the same sort of thing it will get/keep them at a half decent baseling fittness, I do about 5/6 mile a on a bike aday and 99% of it is free running so when they need to shit or piss they do without any sudden jurk ect, Plus a walk in the evening,
But just before the season is here you want to do some short hard runs after a ball of some sort, and do this till they tire then walk them for 10 mins and do the same again and build up to there running more and more at a time,
That way it builds the muscles back up to sprinting that they dont get walking/jogging beside the c