I tell my team, distance runners have no talent, only fitness. Since I'm not afraid of hyperbole, I'll hold to that line. I had a kid in track last year who ran 4:57 1600 on about 12-15 miles a week, all either at jogging warm-up/cool down pace or some sort of interval workout. I ran 4:33 for the mile off 40-50 miles a week. Both of us ran into our limit because of training, not talent. I'm sure if I ran 70-80, 80-100, 100-120... miles a week I would have run faster. I tell my top runners that the difference between them and the winners of the races they run is fitness, mileage.