I am a 15:30/32:30/1:11/2:34 (only ran one marathon) guy. I am running 90mpw right now with a focus on a fall half and full marathon, which I have successfully held for a long time before. All of my runs are going great. I feel relaxed on easy days. I run my long runs and tempos on a measured, marked rail trail and am hitting phenomenal splits for them, some of my best ever. My MVO2 runs, however, are terrible. Today I ran 6x1000, 4x400 with a 3:00 rest (6:00 between 1000s and 400s to change into spikes) in 3:08-3:13 and then 74s. I couldn't go any faster. Those 1000s were barely faster than my pace for 20-25:00 tempo runs. A year ago, I could have done this workout in 3:00-3:02, 68-70. In the interim I ran a good marathon, had a bout of anemia, and then got healthy from that around April.
Any advice? I'm thinking of getting my VO2max/heart rate zones tested and starting to do more of these workouts for time/heart rate.