First: I'm supposed to have my hardest fast run today and my last hard long run Saturday. Unfortunately, it's 35 degrees today and it's going to rain all day Saturday. I could move today's run to tomorrow, but it'll be windy, so maybe Thursday. Saturday's run could move to Sunday, but it'll be colder and it starts to mess up next week's plan, so maybe I could do it Friday. Except... I can't run hard Thursday AND Friday. And I have a hill run planned for Thursday anyway.
Second: Saw an interesting article on core workouts for runners http://m.runnersworld.com/workouts/fast-abs?page=single In it, it points out the importance of different core muscles for 1) speed 2) uphills 3) downhills 4) endurance and 5) lateral movement and gives exercises to address each. My question: why not run fast, run uphill, run downhill, run long and run on twisting trails - wouldn't that be more specific?