I'm following the plan basically verbatim. Had about six weeks of Phase 1 (50, 50, 50, 53, 53, 53 miles) and now I'm currently in Phase 2.
I've ran two 64 mile weeks, a 56 mile week, and I'm currently in the middle of a 74 mile week. Not only has my easy pace dropped to about 8:27 pace (it was usually 7:40-ish), but I'm flopping almost all of the workouts. I'm finishing them but I'm dropping way off pace by the end. I used to do a lot of 200-400m mile paced reps in the past and I feel like I've lost all of that "miler" power.
I decided run a 10K with no taper this weekend and I ran incredibly bad. Heat and humidity was poor and I only managed a 41:00 when I usually can run mid-38 with ease.
So what is happening here? Am I just adapting to beat down? Or is all this threshold work killing my speed?
FWIW: Age 39. PR's in my 30's - Mile: 4:50, 5K PR: 17:25. 10K PR: 38:05. This is my first marathon training cycle.