I ran 17:59 off football practices and a 5k XC meet per week. My summer base was 10-15 mpw in the summer. My long run was 3.5 miles. My winter training was basketball and spring track was 15 mpw alternating between 4 miles easy and 8x400 workouts. I ran 4:38 for 1600m. Between FB/BB that's a lot of 5-10 second sprints accumulating over a season.
Two years later, I was hitting 16:40 on 40 mpw.
Fifteen years later, I now run high 15:xx for 5k and high 4:20s for the mile.