Just to follow up, my second cycle of the Big Vert plan and the race I used it for at the end of October went great. I did just about all the workouts on the plan and on race day felt strong throughout what is the longest and toughest event I’ve done.
Here is a figures comparison of the two run throughs: https://www.blog.roblunn.com/2021/11/big-vert-comparsion-first-vs-second.html
Scott (Semple), I religiously took Mondays off following your advice and didn’t have any problems getting started on the Tuesday. I felt pretty good throughout the training plan, too.
As to the question of declining flat speed. I’m not sure about it now as I realised after writing the above post that some of my aerobic tests might have been flawed. However, it stands to reason that you’re not going to get better at something you don’t practice much. You probably will lose or at least not improve flat speed or economy when running mainly on the hills and hiking. But, as Scott Johnston hints at above, flat speed is not the point of this plan.
Either way, I found the plan great for getting used to training with lots of elevation gain. It opened my eyes up to a different type of training.
Going forward, in training for similar types of ultras, I’m going to use the Big Vert plan with a bit more variety in terrain and some other elements. Mainly because it was such a good plan that I want to make it one I can use more or less continually while still being able to develop all areas of my running.
So thanks for the plan and the advice given here!