Tl;dr considering the goal is to raise FTP, is it useful to progress in base phase past level 9 of Sweet spot? Or is it better to move to Threshold workouts instead?
Longer version:
I have been following a polarized(??) approach to base phase with 2 long SS workouts per week and 3-4 Z2 workouts. Over the course of 5 weeks I have built up to level 9 of sweet spot, just finishing Picuris +3 today with a level 3 difficulty rating, so although demanding wasn’t exhauting, definitely not all out.
I have another couple of weeks planned that would take my SS progression towards level 10 or perhaps 11, depending on how things go, hopefully building up to complete Phoenix +2 which is 75 continuous minutes between 90-95%.
Beyond that, my plan (self-designed) will consist of 4 weeks of similar structure that replaces SS workouts with Threshold workouts, building up to complete Pioneer +3 and Zemlya which are long (1x45 & 2x30) intervals at or close to FTP.
1- am I progressing too fast? considering this is base phase…
2- if so, could my fast SS progression be an indicator of an FTP set too low?
3- even though I very much enjoy building up my ability to sustain high SS for longer and longer durations, my real goal is to raise my FTP. Am I better off pivoting to Threshold work sooner and building that up instead? or keep going with my current plan?
4- Considering motivation and recovery have been through the roof, what are the physiological benefits of either zones? which would provide the best bang for the time buck?
I don’t have any goal events. I train for the sake of it, I love the training process and the riding I do is long solo rides, irish weather allowing… otherwise all indoors
My current levels are Endurance 7.0, Tempo 6.2, SS 9.0, Threshold 1.9, and the rest at 1.0
If you want to focus purely on FTP gains without any peaks and timing do vo2 max block (3 weeks of hammering vo2 max workouts) and then follow with FTP work after resting.
If you want to increase TTE - go longer than harder. You can do both worlds and hammer threshold workouts 3x a week for a long time. This has given me over 100W FTP increase in noob gains during my first year and 10W increase in second year (but I have improved a lot in many other aspects like endurance shorter power and power after 2000kJ). So as you see it all depends where you are and your mileage can vary.
If you want to be almost sure your FTP will increase - vo2 max block is the best guess. You will be dying on and off the bike but it works like a charm every time. Your TTE will be shorter after, but doing SST and FTP will improve that over time.
If you want more sensible, long term approach - increase a volume by doing a lot of Z2 work. Then hammer vo2, and some threshold still doing a lot of Z2.
I have omitted the levels deliberately because they are highly skewed by intensity not duration, and personally I do not care about them at all so I cannot relate.
I second the vo2 max session suggestion to raise ftp over SS. I can do 3hr straight of SS. I think riding a vo2 session is better and much harder. Never really felt like I could ride ftp easier or longer from SS work, but have had ftp watts feel relatively easier by stretching my Vo2max intervals. I have also had the SS work feel easier from solid vo2max work, but not the other way around.
This said, I may also have a very well developed aerobic system so less benefit from SS, whereas you could still have larger gains from less intense riding if your still getting noticeable benefit from your SS.