Low Mileage Runner wrote:
What were your "speed work" days like? I think improving that top end turnover IS important, but can mean a lot of different things. If you had days that were specifically about speed work towards the end of the build, that could have built up some fatigue there as a new training stimulus, when really you needed to get fresh. You can get a lot of the benefits of improving running economy that you're looking for by consistently doing drills and strides. Doesn't have to be the main thing of any day, it can be at the end of a training run or after a workout. 3-5x a week. To work on speed consistently like this is a more sustainable way for many people to make faster paces feel smoother during a marathon build, rather than lumping speed work in towards the end.
I agree with the poster who said that those MLR days are important in the last month or so for maintaining fitness as you get into the taper.
Also, I know you said you hit some high mileage, but maybe as a relatively new runner, your legs just don't have that true marathon fatigue resistance yet. It's a slow adaptation and it will come, especially after you absorb all this training. My friend just ran their third marathon and, though they slowed down a bit in the last ~4 miles, they held on for a PB and felt better recovered walking around afterwards than in previous marathons. Speculated that it just gets easier for your legs to take that pounding the more times you do it.
A typical speed day was 10 x 400 at around 5:40 per mile in substitute for the MLR. This would occur after about a 3 mile warmup, followed by a similar cool down at Z2 HR. In total, I did 2 of these workouts in substitute for the MLRs. I do not think that my loss of endurance can solely be attributed to this... I think there was more of a chronic overload/fatigue problem going on in general.
Regarding the mileage, I agree that it was too much, too soon. About 75-80 mpw would have been a better target. I'll aim for this during the next build. I am sure that I can tolerate that volume after what I just did/mostly adapted to.
After a few weeks of recovery, I also think that doing a short half marathon build for a January race would be a good way for me to keep my fitness and build up my top end without forcing it during a marathon build.