this is what i do and this is what works for me (so far):
i run at the track in my university. one lap of that track is 1/4 of a mile. i usually run 12 laps or so which means 3 miles. now, i run for 1/2 a lap where i am sprinting and then for the remaining 1/2 of the track i just walk.
it has helped me build up my endurance although i dont need it so much. my goal is to lose fat and this seems to be doing the job
