Since October, I've been running around 15-20 miles per week (not a lot, I know). This generally consists of 3 workouts each week (track session, intervals, hills, etc). I used to run 30-35 mpw, but in October I started having shin problems so replaced my easy runs 3x a week with stationary bike (it's what I have access to at my gym).
This system of cross training on easy days has worked surprisingly well for me - I've run PBs from 1500-5k. I've also noticed I go into workouts less tired. So I haven't gone back to more running yet as I'm waiting until track season is over to change anything (in the UK, so it's still track season for us).
Going into my final year of high school, I want to get faster, especially over 3000 and 5000 since I'm a steepler moving up next year from 1500/2000sc to 3000sc. Eg. I'd like to take my 5k from 17:5x to at least sub 17:30, preferably closer to 17 flat, 3k from 10:00 to around 9:45.
Would the best way to do this be to build my mileage back up, or keep biking since it's been working for me so far this year? I know the girls I'm competing with are running 30-40 mpw all winter, so although I've run PBs cross training this year, maybe I'd be faster if I was running further too?