I just finished my freshman year of cross country and was wondering how I could come back next year faster. My PR is 22 minutes and I'm looking at a long term goal of sub 18. I think what I need to do is improve my endurance. I'm going to work my way up to 60-70 mpw and run that to next March. Then I will start incorporating tempo runs, intervals, hills, and long runs. My question is how should I build my aerobic base throughout the winter so I am running 60-70 mpw. I don't have a lot of talent. I am 5'7", 125 pounds