I'm 16 years old, I've been running for about a year and a half, building up to 40 miles a week the first six months and for the past year have been running consistently at that mileage. My last race was a 5k, I struggled to break 20 minutes, ended up running 19:49.
Why is this? I can run 7 miles at 6:40 pace and feel good. I have SOME top end speed; A 61 second 400m. Yet I'm awful when it comes to anything around 5k.
My week is generally comprised of a speed session (I've only started doing them seriously the past couple weeks), a steady state run; 7-8 miles around half marathon pace and a 1hr30-1hr40 long run. When it comes to speed work, I can't do anything too intense or do more than 1 workout a week otherwise I just burnout my legs.
P.S. No, I'm not a girl and no, I'm not fat. I'm 5'6" and 110 pounds.