I follow a few elite ultra mountain runners on Strava and was shocked by these guys casually dropping a 15-16 min 5k off of just jogging around in the mountains. Like WTF, I know guys that do all the right stuff with diet, mileage, speed work etc. and still can't break 17 minutes in the 5k. How can these guys just eat candy and jog in the mountains and just casually run a 15-16 min 5k?