Of course it would all depend on how fit you want your mutt to be,what type of work you want it to do etc. All that would dictate if you would follow special diets,training patterns and type of excercise.
For example,and im not saying anyone on here would do this because i know we are all fine upstanding citizens on here,but, if you drive round with your dog, peering into fields, slipping it on stuff,you might want more of a sprinter than say someone who goes out all day mooching about? The moocher would probably want a dog that can last a full days walking with a couple of runs here and ther