Hi there. It depends on your goals. I would do threshold progression , but before that I will take week of recovery. You could do vo2 max progression. Both will increase your ftp or at least increase your fatigue resistance.
First off, no donât add the 5W and start over, IMO. Itâs kind of a waste of energy because physiologically itâs the same workout.
Thereâs no real âmax timeâ at 90 min. Iâve taken people out to 2hrs before. Could go longer than that.
Some options: reduce rest between intervals or eliminate it entirely. Can you sit at 90% for 90 min? Extend to 2 or 2.5 hours (wouldnât ever go beyond that without testing FTP again). Add bursts to your SST workouts. I do this a lot and my athletes seem to really like it as it breaks the monotony. The bursts I add are typically just accelerate leg speed for 10s, so if youâre at 90rpm doing 90%, you just bring your leg speed up to 110rpm or so and then settle back in at 90rpm/90%. You can put it in your workout as 125 or so % if youâre an erg guy.
Given that youâre doing mixed progression, you can switch to a sweet spot maintenance where you do 60-90 min workouts and then work the VO2 differently/more intensely, as well.
That said, there comes a time in everyoneâs progression as an athlete where they need to change things up, so you might consider some other suggestions such as working closer to FTP (5-10W below) and extending time there, or doing something more FTP growth focused like over-unders.
In my experience, the SST progression is great for establishing a high-end aerobic base, particularly on a time crunched schedule, and while I do give sweet spot throughout the year, I do not do progressions like this all year long. SST for most guys after base is about threshold/sustained power maintenance with less fatigue, so I use it quite a bit during race season when guys are doing weekend crits, they do 3x20 mid-week or something like that.
Let me know if you have specific questions about any of that. happy to help!
thank you!
how much more benefit is there going to 120 min once you hit 90 min - rather than switching to 5-10 watts below FTP?
I feel like in my biking âcareerâ right now 90 min is about as much as I wanna endure of something thatâs pretty hard. (maybe thatâll change some day).
Yeah if I were you I would focus on trying to push FTP up with a mixed block of FTP work (threshold and/or over-unders) and VO2 based on what youâve said. Do that for 1-2 cycles of 3 weeks or so, so probably 6 total workouts. The trick is progressing time at 5-10W below threshold, but you need to be quite a bit less aggressive about it. My rule of thumb is ~10% TiZ per week. So if you start at 40 min (e.g.), next week push to 44 or 45 with a 2x22 or 3x15. I typically keep threshold intervals no shorter than 10 min, and I seek to get to 15-25 min intervals as quickly as possible.
A typical progression might be something like 3x12 â 4x10 â 2x20 â 2x22 or 3x15 â 3x16 or 2x24 â 3x17 â etc. progressing up to 3x20/2x30 depending on the athlete. Having done a lot of SST extension work, you can probably skip the 10-12min stuff and dive right in to a 2x20 at 10W below threshold I would guess. (BTW 10W below threshold assumes someone in that 250-300W range, if your raw FTP number is lower, you can go more like 5⌠point is to be somewhat notably BELOW threshold rather than right at it or certainly not above it. I typically have people kind of ride by RPE. If youâre above threshold, right about that 12 min mark of an interval, youâll know.)
Do over unders. 4 minutes at 90%. 1 minute at 120ish%.
Start with 3 Ă 15. Then do 4 Ă 15. Then 3 Ă 20. Then 3 Ă 25. You get the idea.
So youâre mostly pushing familiar SS watts, but with some challenge.
Enjoy!
ETA: Or do what @kurt.braeckel said. Depends on how ADHD you are 
Yeah thatâs the Dean Golich approach, and it works well with experienced/well-trained riders for sure. If youâve done progressions up to 60min at threshold and youâre revisiting âknown territoryâ, you donât need to be quite as conservative. When youâre pushing things, thatâs when I take the slower approach.
Will doâŚthank you!!
Thereâs a âteam sweet spotâ you can join. That has a good library of workouts which progress TTE
They were referring to this TR team with custom sweet spot workouts
I canât access that any more as Iâm not a subscriber.
Iâve since worked out the (actually remarkably easy!) Intervals workout builder though, so can knock up a session in a couple of minutes now 
Did you ever figure this out? I now have the same problem!
May not be the answer youâre looking for, or maybe I misunderstood the question, but intervals.icu has that already⌠thatâs where @FergusYL got the table they copied here.
Were you replying to me? If so, thanks for the reply, but my question was about tracking time in SS zone during the ride on the Garmin, not after.
Yes, replying to you; and sorry, had misunderstood the question.
Nope. Weirdly, itâs just not something any of the computers seem to do. The best workaround I could find was to hit the lap button on stretches where I knew I could stay in sweet spot, then end it when the terrain hit a point I couldnât hold the power steady anymore, like long downhills or lots of rollers. Then just keep a running total of time in zone in mind.
Itâs pretty annoying considering how common SST training is across training apps, platforms, and philosophies.
https://apps.garmin.com/en-US/apps/95fc3b69-6c3c-4618-a2de-f68ffca35360
This certainly isnât perfect but you can set a custom floor that you have to exceed (just canât give a ceiling).
Thread here: Announcing "Endurance in Zone" for Garmin devices
@torhovland is the creator
I have not tried this but could you use Garminâs native Time In Zone and customize your power zones?
Default:
Sweetspot specific:
Yeah, Iâve considered that but I do occasionally use it to track time in zone for Threshold, too. And just knowing the zones were off would inevitably kick up some kind of Telltale Heart scenario on the bike and drive me a little crazy.
I was just checking around on the Connect IQ store and thereâs a decent looking time in zone datafield. I may reach out to the developer and see if he could add Sweet Spot in there, with donations forthcoming.
Garmin has native TiZ data fields too, just not a SS one.
Anyone currently making use of the âMore Sweetspot!â Teamâs library of âSS90â workouts might want to take a look at this:
No reply from TR so far to my questions about this, heightening my concern that this extremely useful feature - which in effect provides us with shared libraries of Custom workouts - is one step nearer to being binned for good. 
If this is something that you make use of, and would be impacted by its loss, I suggest speaking upâŚ